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Willems E, Janssens KLPM, Dekker LRC, van de Vosse FN, Cluitmans MJM, Bovendeerd PHM. Strain-controlled electrophysiological wave propagation alters in silico scar-based substrate for ventricular tachycardia. Front Physiol 2024; 15:1330157. [PMID: 38655031 PMCID: PMC11036413 DOI: 10.3389/fphys.2024.1330157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Accepted: 03/21/2024] [Indexed: 04/26/2024] Open
Abstract
Introduction: Assessing a patient's risk of scar-based ventricular tachycardia (VT) after myocardial infarction is a challenging task. It can take months to years after infarction for VT to occur. Also, if selected for ablation therapy, success rates are low. Methods: Computational ventricular models have been presented previously to support VT risk assessment and to provide ablation guidance. In this study, an extension to such virtual-heart models is proposed to phenomenologically incorporate tissue remodeling driven by mechanical load. Strain amplitudes in the heart muscle are obtained from simulations of mechanics and are used to adjust the electrical conductivity. Results: The mechanics-driven adaptation of electrophysiology resulted in a more heterogeneous distribution of propagation velocities than that of standard models, which adapt electrophysiology in the structural substrate from medical images only. Moreover, conduction slowing was not only present in such a structural substrate, but extended in the adjacent functional border zone with impaired mechanics. This enlarged the volumes with high repolarization time gradients (≥10 ms/mm). However, maximum gradient values were not significantly affected. The enlarged volumes were localized along the structural substrate border, which lengthened the line of conduction block. The prolonged reentry pathways together with conduction slowing in functional regions increased VT cycle time, such that VT was easier to induce, and the number of recommended ablation sites increased from 3 to 5 locations. Discussion: Sensitivity testing showed an accurate model of strain-dependency to be critical for low ranges of conductivity. The model extension with mechanics-driven tissue remodeling is a potential approach to capture the evolution of the functional substrate and may offer insight into the progression of VT risk over time.
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Affiliation(s)
- Evianne Willems
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
| | - Koen L. P. M. Janssens
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
| | - Lukas R. C. Dekker
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
- Department of Cardiology, Catharina Hospital, Eindhoven, Netherlands
| | - Frans N. van de Vosse
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
| | - Matthijs J. M. Cluitmans
- Maastricht University Medical Center, Maastricht, Netherlands
- Philips Research Eindhoven, Eindhoven, Netherlands
| | - Peter H. M. Bovendeerd
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
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2
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Motchon YD, Sack KL, Sirry MS, Kruger M, Pauwels E, Van Loo D, De Muynck A, Van Hoorebeke L, Davies NH, Franz T. Effect of biomaterial stiffness on cardiac mechanics in a biventricular infarcted rat heart model with microstructural representation of in situ intramyocardial injectate. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3693. [PMID: 36864599 PMCID: PMC10909490 DOI: 10.1002/cnm.3693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 11/19/2022] [Accepted: 01/29/2023] [Indexed: 05/13/2023]
Abstract
Intramyocardial delivery of biomaterials is a promising concept for treating myocardial infarction. The delivered biomaterial provides mechanical support and attenuates wall thinning and elevated wall stress in the infarct region. This study aimed at developing a biventricular finite element model of an infarcted rat heart with a microstructural representation of an in situ biomaterial injectate, and a parametric investigation of the effect of the injectate stiffness on the cardiac mechanics. A three-dimensional subject-specific biventricular finite element model of a rat heart with left ventricular infarct and microstructurally dispersed biomaterial delivered 1 week after infarct induction was developed from ex vivo microcomputed tomography data. The volumetric mesh density varied between 303 mm-3 in the myocardium and 3852 mm-3 in the injectate region due to the microstructural intramyocardial dispersion. Parametric simulations were conducted with the injectate's elastic modulus varying from 4.1 to 405,900 kPa, and myocardial and injectate strains were recorded. With increasing injectate stiffness, the end-diastolic median myocardial fibre and cross-fibre strain decreased in magnitude from 3.6% to 1.1% and from -6.0% to -2.9%, respectively. At end-systole, the myocardial fibre and cross-fibre strain decreased in magnitude from -20.4% to -11.8% and from 6.5% to 4.6%, respectively. In the injectate, the maximum and minimum principal strains decreased in magnitude from 5.4% to 0.001% and from -5.4% to -0.001%, respectively, at end-diastole and from 38.5% to 0.06% and from -39.0% to -0.06%, respectively, at end-systole. With the microstructural injectate geometry, the developed subject-specific cardiac finite element model offers potential for extension to cellular injectates and in silico studies of mechanotransduction and therapeutic signalling in the infarcted heart with an infarct animal model extensively used in preclinical research.
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Affiliation(s)
- Y. D. Motchon
- Biomedical Engineering Research Centre, Division of Biomedical Engineering, Department of Human BiologyUniversity of Cape TownCape TownSouth Africa
| | - Kevin L. Sack
- Biomedical Engineering Research Centre, Division of Biomedical Engineering, Department of Human BiologyUniversity of Cape TownCape TownSouth Africa
- Department of SurgeryUniversity of California at San FranciscoSan FranciscoCaliforniaUSA
| | - M. S. Sirry
- Department of Biomedical Engineering, School of Engineering and ComputingAmerican International UniversityAl JahraKuwait
| | - M. Kruger
- Cardiovascular Research Unit, MRC IUCHRUUniversity of Cape TownCape TownSouth Africa
| | - E. Pauwels
- Centre for X‐ray Tomography, Department of Physics and AstronomyGhent UniversityGhentBelgium
- Nuclear MedicineUniversity Hospitals LeuvenLeuvenBelgium
| | - D. Van Loo
- Centre for X‐ray Tomography, Department of Physics and AstronomyGhent UniversityGhentBelgium
- XRE nv, Bollebergen 2B box 1, 9052GhentBelgium
| | - A. De Muynck
- Centre for X‐ray Tomography, Department of Physics and AstronomyGhent UniversityGhentBelgium
| | - L. Van Hoorebeke
- Centre for X‐ray Tomography, Department of Physics and AstronomyGhent UniversityGhentBelgium
| | - Neil H. Davies
- Cardiovascular Research Unit, MRC IUCHRUUniversity of Cape TownCape TownSouth Africa
| | - Thomas Franz
- Biomedical Engineering Research Centre, Division of Biomedical Engineering, Department of Human BiologyUniversity of Cape TownCape TownSouth Africa
- Bioengineering Science Research Group, Faculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonUK
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3
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Wilson AJ, Sands GB, LeGrice IJ, Young AA, Ennis DB. Myocardial mesostructure and mesofunction. Am J Physiol Heart Circ Physiol 2022; 323:H257-H275. [PMID: 35657613 PMCID: PMC9273275 DOI: 10.1152/ajpheart.00059.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 05/23/2022] [Accepted: 05/23/2022] [Indexed: 11/22/2022]
Abstract
The complex and highly organized structural arrangement of some five billion cardiomyocytes directs the coordinated electrical activity and mechanical contraction of the human heart. The characteristic transmural change in cardiomyocyte orientation underlies base-to-apex shortening, circumferential shortening, and left ventricular torsion during contraction. Individual cardiomyocytes shorten ∼15% and increase in diameter ∼8%. Remarkably, however, the left ventricular wall thickens by up to 30-40%. To accommodate this, the myocardium must undergo significant structural rearrangement during contraction. At the mesoscale, collections of cardiomyocytes are organized into sheetlets, and sheetlet shear is the fundamental mechanism of rearrangement that produces wall thickening. Herein, we review the histological and physiological studies of myocardial mesostructure that have established the sheetlet shear model of wall thickening. Recent developments in tissue clearing techniques allow for imaging of whole hearts at the cellular scale, whereas magnetic resonance imaging (MRI) and computed tomography (CT) can image the myocardium at the mesoscale (100 µm to 1 mm) to resolve cardiomyocyte orientation and organization. Through histology, cardiac diffusion tensor imaging (DTI), and other modalities, mesostructural sheetlets have been confirmed in both animal and human hearts. Recent in vivo cardiac DTI methods have measured reorientation of sheetlets during the cardiac cycle. We also examine the role of pathological cardiac remodeling on sheetlet organization and reorientation, and the impact this has on ventricular function and dysfunction. We also review the unresolved mesostructural questions and challenges that may direct future work in the field.
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Affiliation(s)
- Alexander J Wilson
- Department of Radiology, Stanford University, Stanford, California
- Stanford Cardiovascular Institute, Stanford University, Stanford, California
| | - Gregory B Sands
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Ian J LeGrice
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Alistair A Young
- Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
- Department of Biomedical Engineering, King's College London, London, United Kingdom
| | - Daniel B Ennis
- Department of Radiology, Stanford University, Stanford, California
- Veterans Administration Palo Alto Health Care System, Palo Alto, California
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4
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Muiño-Mosquera L, De Backer J. Cardiomyopathy in Genetic Aortic Diseases. Front Pediatr 2021; 9:682390. [PMID: 34336739 PMCID: PMC8319542 DOI: 10.3389/fped.2021.682390] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Accepted: 06/22/2021] [Indexed: 11/13/2022] Open
Abstract
Genetic aortic diseases are a group of illnesses characterized by aortic aneurysms or dissection in the presence of an underlying genetic defect. They are part of the broader spectrum of heritable thoracic aortic disease, which also includes those cases of aortic aneurysm or dissection with a positive family history but in whom no genetic cause is identified. Aortic disease in these conditions is a major cause of mortality, justifying clinical and scientific emphasis on the aorta. Aortic valve disease and atrioventricular valve abnormalities are known as important additional manifestations that require careful follow-up and management. The archetype of genetic aortic disease is Marfan syndrome, caused by pathogenic variants in the Fibrillin-1 gene. Given the presence of fibrillin-1 microfibers in the myocardium, myocardial dysfunction and associated arrhythmia are conceivable and have been shown to contribute to morbidity and mortality in patients with Marfan syndrome. In this review, we will discuss data on myocardial disease from human studies as well as insights obtained from the study of mouse models of Marfan syndrome. We will elaborate on the various phenotypic presentations in childhood and in adults and on the topic of arrhythmia. We will also briefly discuss the limited data available on other genetic forms of aortic disease.
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Affiliation(s)
- Laura Muiño-Mosquera
- Department of Pediatrics, Division of Pediatric Cardiology, Ghent University Hospital, Ghent, Belgium.,Center for Medical Genetics, Ghent University Hospital, Ghent, Belgium
| | - Julie De Backer
- Center for Medical Genetics, Ghent University Hospital, Ghent, Belgium.,Department of Cardiology, Ghent University Hospital, Ghent, Belgium
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5
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Le B, Ferreira P, Merchant S, Zheng G, Sutherland MR, Dahl MJ, Albertine KH, Black MJ. Microarchitecture of the hearts in term and former-preterm lambs using diffusion tensor imaging. Anat Rec (Hoboken) 2020; 304:803-817. [PMID: 33015923 DOI: 10.1002/ar.24516] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/31/2020] [Accepted: 06/30/2020] [Indexed: 12/13/2022]
Abstract
Diffusion tensor imaging (DTI) is an MRI technique that can be used to map cardiomyocyte tracts and estimate local cardiomyocyte and sheetlet orientation within the heart. DTI measures diffusion distances of water molecules within the myocardium, where water diffusion generally occurs more freely along the long axis of cardiomyocytes and within the extracellular matrix, but is restricted by cell membranes such that transverse diffusion is limited. DTI can be undertaken in fixed hearts and it allows the three-dimensional mapping of the cardiac microarchitecture, including cardiomyocyte organization, within the whole heart. The objective of this study was to use DTI to compare the cardiac microarchitecture and cardiomyocyte organization in archived fixed left ventricles of lambs that were born either preterm (n = 5) or at term (n = 7), at a postnatal timepoint equivalent to about 6 years of age in children. Although the findings support the feasibility of retrospective DTI scanning of fixed hearts, several hearts were excluded from DTI analysis because of poor scan quality, such as ghosting artifacts. The preliminary findings from viable DTI scans (n = 3/group) suggest that the extracellular compartment is altered and that there is an immature microstructural phenotype early in postnatal life in the LV of lambs born preterm. Our findings support a potential time-efficient imaging role for DTI in detecting abnormal changes in the microstructure of fixed hearts of former-preterm neonates, although further investigation into factors that affect scan quality is required.
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Affiliation(s)
- Bianca Le
- Department of Anatomy and Developmental Biology and Biomedicine Discovery Institute, Monash University, Victoria, Australia
| | | | - Samer Merchant
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA
| | - Gang Zheng
- Monash Biomedical Imaging, Monash University, Victoria, Australia
| | - Megan R Sutherland
- Department of Anatomy and Developmental Biology and Biomedicine Discovery Institute, Monash University, Victoria, Australia
| | - Mar Janna Dahl
- Department of Pediatrics, University of Utah, Salt Lake City, Utah, USA
| | - Kurt H Albertine
- Department of Pediatrics, University of Utah, Salt Lake City, Utah, USA
| | - Mary Jane Black
- Department of Anatomy and Developmental Biology and Biomedicine Discovery Institute, Monash University, Victoria, Australia
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6
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Stanley A, Athanasuleas C, Buckberg G. How His bundle pacing prevents and reverses heart failure induced by right ventricular pacing. Heart Fail Rev 2020; 26:1311-1324. [PMID: 32318885 DOI: 10.1007/s10741-020-09962-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Ideal heart performance demands vigorous systolic contractions and rapid diastolic relaxation. These sequential events are precisely timed and interdependent and require the rapid synchronous electrical stimulation provided by the His-Purkinje system. Right ventricular (RV) pacing creates slow asynchronous electrical stimulation that disrupts the timing of the cardiac cycle and results in left ventricular (LV) mechanical asynchrony. Long-term mechanical asynchrony produces LV dysfunction, remodeling, and clinical heart failure. His bundle pacing preserves synchronous electrical and mechanical LV function, prevents or reverses RV pacemaker-induced remodeling, and reduces heart failure.
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Affiliation(s)
- Alfred Stanley
- Cardiovascular Associates of the Southeast, Birmingham, AL, USA
| | - Constantine Athanasuleas
- Division of Cardiothoracic Surgery, Department of Surgery, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Gerald Buckberg
- Division of Cardiac Surgery, Department of Surgery, Cardiovascular Center at UCLA, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
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7
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Nielles-Vallespin S, Scott A, Ferreira P, Khalique Z, Pennell D, Firmin D. Cardiac Diffusion: Technique and Practical Applications. J Magn Reson Imaging 2019; 52:348-368. [PMID: 31482620 DOI: 10.1002/jmri.26912] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 08/13/2019] [Accepted: 08/14/2019] [Indexed: 12/12/2022] Open
Abstract
The 3D microarchitecture of the cardiac muscle underlies the mechanical and electrical properties of the heart. Cardiomyocytes are arranged helically through the depth of the wall, and their shortening leads to macroscopic torsion, twist, and shortening during cardiac contraction. Furthermore, cardiomyocytes are organized in sheetlets separated by shear layers, which reorientate, slip, and shear during macroscopic left ventricle (LV) wall thickening. Cardiac diffusion provides a means for noninvasive interrogation of the 3D microarchitecture of the myocardium. The fundamental principle of MR diffusion is that an MRI signal is attenuated by the self-diffusion of water in the presence of large diffusion-encoding gradients. Since water molecules are constrained by the boundaries in biological tissue (cell membranes, collagen layers, etc.), depicting their diffusion behavior elucidates the shape of the myocardial microarchitecture they are embedded in. Cardiac diffusion therefore provides a noninvasive means to understand not only the dynamic changes in cardiac microstructure of healthy myocardium during cardiac contraction but also the pathophysiological changes in the presence of disease. This unique and innovative technology offers tremendous potential to enable improved clinical diagnosis through novel microstructural and functional assessment. in vivo cardiac diffusion methods are immediately translatable to patients, opening new avenues for diagnostic investigation and treatment evaluation in a range of clinically important cardiac pathologies. This review article describes the 3D microstructure of the LV, explains in vivo and ex vivo cardiac MR diffusion acquisition and postprocessing techniques, as well as clinical applications to date. Level of Evidence: 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;52:348-368.
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Affiliation(s)
- Sonia Nielles-Vallespin
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
| | - Andrew Scott
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
| | - Pedro Ferreira
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
| | - Zohya Khalique
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
| | - Dudley Pennell
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
| | - David Firmin
- Cardiovascular MR Unit, Royal Brompton And Harefield NHS Foundation Trust, London, UK.,NHLI, Imperial College of Science, Technology and Medicine, London, UK
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8
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Lunkenheimer PP, Niederer P, Stephenson RS, Redmann K, Batista RV, Smerup M, Anderson RH. What is the clinical significance of ventricular mural antagonism? Eur J Cardiothorac Surg 2019; 53:714-723. [PMID: 29136124 DOI: 10.1093/ejcts/ezx382] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 10/01/2017] [Indexed: 11/15/2022] Open
Abstract
Recent morphological studies provide evidence that the ventricular walls are arranged as a 3D meshwork of aggregated cardiomyocyte chains, exhibiting marked local structural variations. In contrary to previous findings, up to two-fifths of the chains are found to have a partially transmural alignment, thus deviating from the prevailing tangential orientation. Upon contraction, they produce, in addition to a tangential force, a radial force component that counteracts ventricular constriction and aids widening of the ventricular cavity. In experimental studies, we have provided evidence for the existence of such forces, which are auxotonic in nature. This is in contrast to the tangentially aligned myocytes that produce constrictive forces, which are unloading in nature. The ventricular myocardium is, therefore, able to function in an antagonistic fashion, with the prevailing constrictive forces acting simultaneously with a dilatory force component. The ratio of constrictive to dilating force varies locally according to the specific mural architecture. Such antagonism acts according to local demands to preserve the ventricular shape, store the elastic energy that drives the fast late systolic dilation and apportion mural motion to facilitate the spiralling nature of intracavitary flow. Intracavitary pressure and flow dynamics are thus governed concurrently by ventricular constrictive and dilative force components. Antagonistic activity, however, increases deleteriously in states of cardiac disease, such as hypertrophy and fibrosis. ß-blockade at low dosage acts selectively to temper the auxotonic forces.
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Affiliation(s)
- Paul P Lunkenheimer
- Department of Experimental Cardiac- and Thoraco-Vascular Surgery, University Hospital Muenster, Muenster, Germany
| | - Peter Niederer
- Institute of Biomedical Engineering, ETH, University of Zurich, Zurich, Switzerland
| | - Robert S Stephenson
- Comparative Medicine Laboratory, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Klaus Redmann
- Department of Experimental Cardiac- and Thoraco-Vascular Surgery, University Hospital Muenster, Muenster, Germany
| | | | - Morten Smerup
- University Hospital, Thoraxkirurgisk Klinik, Copenhagen, Denmark
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9
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Ferreira PF, Nielles-Vallespin S, Scott AD, de Silva R, Kilner PJ, Ennis DB, Auger DA, Suever JD, Zhong X, Spottiswoode BS, Pennell DJ, Arai AE, Firmin DN. Evaluation of the impact of strain correction on the orientation of cardiac diffusion tensors with in vivo and ex vivo porcine hearts. Magn Reson Med 2017; 79:2205-2215. [PMID: 28734017 DOI: 10.1002/mrm.26850] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 06/07/2017] [Accepted: 07/02/2017] [Indexed: 11/11/2022]
Abstract
PURPOSE To evaluate the importance of strain-correcting stimulated echo acquisition mode echo-planar imaging cardiac diffusion tensor imaging. METHODS Healthy pigs (n = 11) were successfully scanned with a 3D cine displacement-encoded imaging with stimulated echoes and a monopolar-stimulated echo-planar imaging diffusion tensor imaging sequence at 3 T during diastasis, peak systole, and strain sweet spots in a midventricular short-axis slice. The same diffusion tensor imaging sequence was repeated ex vivo after arresting the hearts in either a relaxed (KCl-induced) or contracted (BaCl2 -induced) state. The displacement-encoded imaging with stimulated echoes data were used to strain-correct the in vivo cardiac diffusion tensor imaging in diastole and systole. The orientation of the primary (helix angles) and secondary (E2A) diffusion eigenvectors was compared with and without strain correction and to the strain-free ex vivo data. RESULTS Strain correction reduces systolic E2A significantly when compared without strain correction and ex vivo (median absolute E2A = 34.3° versus E2A = 57.1° (P = 0.01), E2A = 60.5° (P = 0.006), respectively). The systolic distribution of E2A without strain correction is closer to the contracted ex vivo distribution than with strain correction, root mean square deviation of 0.027 versus 0.038. CONCLUSIONS The current strain-correction model amplifies the contribution of microscopic strain to diffusion resulting in an overcorrection of E2A. Results show that a new model that considers cellular rearrangement is required. Magn Reson Med 79:2205-2215, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Pedro F Ferreira
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
| | | | - Andrew D Scott
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
| | - Ranil de Silva
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
| | - Philip J Kilner
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
| | - Daniel B Ennis
- Department of Radiological Sciences, University of California, Los Angeles, California, USA
| | - Daniel A Auger
- Biomedical Engineering, University of Virginia, Charlottesville, Virginia, USA
| | | | | | | | - Dudley J Pennell
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
| | - Andrew E Arai
- NHLBI, National Institutes of Health, Bethesda, Maryland, USA
| | - David N Firmin
- Cardiovascular BRU, Royal Brompton Hospital, London, United Kingdom.,National Heart and Lung Institute, Imperial College, London, United Kingdom
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10
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Nielles-Vallespin S, Khalique Z, Ferreira PF, de Silva R, Scott AD, Kilner P, McGill LA, Giannakidis A, Gatehouse PD, Ennis D, Aliotta E, Al-Khalil M, Kellman P, Mazilu D, Balaban RS, Firmin DN, Arai AE, Pennell DJ. Assessment of Myocardial Microstructural Dynamics by In Vivo Diffusion Tensor Cardiac Magnetic Resonance. J Am Coll Cardiol 2017; 69:661-676. [PMID: 28183509 PMCID: PMC8672367 DOI: 10.1016/j.jacc.2016.11.051] [Citation(s) in RCA: 155] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 10/29/2016] [Accepted: 11/07/2016] [Indexed: 01/23/2023]
Abstract
BACKGROUND Cardiomyocytes are organized in microstructures termed sheetlets that reorientate during left ventricular thickening. Diffusion tensor cardiac magnetic resonance (DT-CMR) may enable noninvasive interrogation of in vivo cardiac microstructural dynamics. Dilated cardiomyopathy (DCM) is a condition of abnormal myocardium with unknown sheetlet function. OBJECTIVES This study sought to validate in vivo DT-CMR measures of cardiac microstructure against histology, characterize microstructural dynamics during left ventricular wall thickening, and apply the technique in hypertrophic cardiomyopathy (HCM) and DCM. METHODS In vivo DT-CMR was acquired throughout the cardiac cycle in healthy swine, followed by in situ and ex vivo DT-CMR, then validated against histology. In vivo DT-CMR was performed in 19 control subjects, 19 DCM, and 13 HCM patients. RESULTS In swine, a DT-CMR index of sheetlet reorientation (E2A) changed substantially (E2A mobility ~46°). E2A changes correlated with wall thickness changes (in vivo r2 = 0.75; in situ r2 = 0.89), were consistently observed under all experimental conditions, and accorded closely with histological analyses in both relaxed and contracted states. The potential contribution of cyclical strain effects to in vivo E2A was ~17%. In healthy human control subjects, E2A increased from diastole (18°) to systole (65°; p < 0.001; E2A mobility = 45°). HCM patients showed significantly greater E2A in diastole than control subjects did (48 ; p < 0.001) with impaired E2A mobility (23°; p < 0.001). In DCM, E2A was similar to control subjects in diastole, but systolic values were markedly lower (40° ; p < 0.001) with impaired E2A mobility (20°; p < 0.001). CONCLUSIONS Myocardial microstructure dynamics can be characterized by in vivo DT-CMR. Sheetlet function was abnormal in DCM with altered systolic conformation and reduced mobility, contrasting with HCM, which showed reduced mobility with altered diastolic conformation. These novel insights significantly improve understanding of contractile dysfunction at a level of noninvasive interrogation not previously available in humans. (J Am Coll Cardiol 2017;69:661–76) Published by Elsevier on behalf of the American College of Cardiology Foundation.
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Affiliation(s)
- Sonia Nielles-Vallespin
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland; Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom.
| | - Zohya Khalique
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Pedro F Ferreira
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Ranil de Silva
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Andrew D Scott
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Philip Kilner
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Laura-Ann McGill
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Archontis Giannakidis
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Peter D Gatehouse
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Daniel Ennis
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Eric Aliotta
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Majid Al-Khalil
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom
| | - Peter Kellman
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland
| | - Dumitru Mazilu
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland
| | - Robert S Balaban
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland
| | - David N Firmin
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
| | - Andrew E Arai
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland
| | - Dudley J Pennell
- Cardiovascular Magnetic Resonance Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom; National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Institute for Health Research Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield National Health Service Foundation Trust, and Imperial College London, London, United Kingdom
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11
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Carruth ED, McCulloch AD, Omens JH. Transmural gradients of myocardial structure and mechanics: Implications for fiber stress and strain in pressure overload. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 122:215-226. [PMID: 27845176 DOI: 10.1016/j.pbiomolbio.2016.11.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Although a truly complete understanding of whole heart activation, contraction, and deformation is well beyond our current reach, a significant amount of effort has been devoted to discovering and understanding the mechanisms by which myocardial structure determines cardiac function to better treat patients with cardiac disease. Several experimental studies have shown that transmural fiber strain is relatively uniform in both diastole and systole, in contrast to predictions from traditional mechanical theory. Similarly, mathematical models have largely predicted uniform fiber stress across the wall. The development of this uniform pattern of fiber stress and strain during filling and ejection is due to heterogeneous transmural distributions of several myocardial structures. This review summarizes these transmural gradients, their contributions to fiber mechanics, and the potential functional effects of their remodeling during pressure overload hypertrophy.
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Affiliation(s)
- Eric D Carruth
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA.
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA.
| | - Jeffrey H Omens
- Department of Bioengineering, University of California San Diego, La Jolla, CA, USA; Department of Medicine, University of California San Diego, La Jolla, CA, USA.
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12
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Oki T, Miyoshi H, Oishi Y, Mizuguchi Y, Iuchi A, Yamada H, Nakatani S. Challenges for 'diastology': contributions from Japanese researchers. J Echocardiogr 2016; 14:93-103. [PMID: 27539160 DOI: 10.1007/s12574-016-0307-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 07/29/2016] [Indexed: 01/08/2023]
Abstract
Diastology is a study to treat diastole of the heart. Transmitral flow and pulmonary venous flow velocities recorded by pulsed Doppler echocardiography provide more important information about left ventricular (LV) diastolic dysfunction [left atrial (LA)-LV coupling] than cardiac catheterization in clinical practice; however, these waveforms are influenced by loading conditions, particularly preload. The early diastolic mitral annular and LV wall motion indices measured by tissue Doppler echocardiography can evaluate LV relaxation abnormality and filling pressure by being relatively preload independent. In addition, the role of concomitant systolic longitudinal dysfunction is well characterized in asymptomatic patients and in patients with heart failure and preserved ejection fraction. Two-dimensional speckle tracking echocardiography is an angle-independent method, and has the potential to evaluate the contraction and relaxation abnormalities in the longitudinal, circumferential, and radial directions of the LV myocardium as well as LV torsion/untwisting and, moreover, deformation of the LA myocardium and large arterial wall. As a result, this new technique can facilitate the early detection of impaired LA-LV-arterial coupling in patients before occurrence of overt heart failure symptoms.
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Affiliation(s)
- Takashi Oki
- Cardiovascular Section, Higashi Tokushima Medical Center, National Hospital Organization, Tokushima, Japan.
| | - Hirokazu Miyoshi
- Cardiovascular Section, Higashi Tokushima Medical Center, National Hospital Organization, Tokushima, Japan
| | - Yoshifumi Oishi
- Cardiovascular Section, Higashi Tokushima Medical Center, National Hospital Organization, Tokushima, Japan
| | - Yukio Mizuguchi
- Cardiovascular Section, Higashi Tokushima Medical Center, National Hospital Organization, Tokushima, Japan
| | - Arata Iuchi
- Cardiovascular Section, Higashi Tokushima Medical Center, National Hospital Organization, Tokushima, Japan
| | - Hirotsugu Yamada
- Department of Cardiovascular Medicine, Tokushima University Hospital, Tokushima, Japan
| | - Satoshi Nakatani
- Division of Functional Diagnostics, Department of Health Sciences, Osaka University Graduate School of Medicine, Osaka, Japan
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13
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Fan L, Yao J, Yang C, Wu Z, Xu D, Tang D. Material stiffness parameters as potential predictors of presence of left ventricle myocardial infarction: 3D echo-based computational modeling study. Biomed Eng Online 2016; 15:34. [PMID: 27044441 PMCID: PMC4820947 DOI: 10.1186/s12938-016-0151-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 03/29/2016] [Indexed: 01/18/2023] Open
Abstract
Background Ventricle material properties are difficult to obtain under in vivo conditions and are not readily available in the current literature. It is also desirable to have an initial determination if a patient had an infarction based on echo data before more expensive examinations are recommended. A noninvasive echo-based modeling approach and a predictive method were introduced to determine left ventricle material parameters and differentiate patients with recent myocardial infarction (MI) from those without. Methods Echo data were obtained from 10 patients, 5 with MI (Infarct Group) and 5 without (Non-Infarcted Group). Echo-based patient-specific computational left ventricle (LV) models were constructed to quantify LV material properties. All patients were treated equally in the modeling process without using MI information. Systolic and diastolic material parameter values in the Mooney-Rivlin models were adjusted to match echo volume data. The equivalent Young’s modulus (YM) values were obtained for each material stress–strain curve by linear fitting for easy comparison. Predictive logistic regression analysis was used to identify the best parameters for infract prediction. Results The LV end-systole material stiffness (ES-YMf) was the best single predictor among the 12 individual parameters with an area under the receiver operating characteristic (ROC) curve of 0.9841. LV wall thickness (WT), material stiffness in fiber direction at end-systole (ES-YMf) and material stiffness variation (∆YMf) had positive correlations with LV ejection fraction with correlation coefficients r = 0.8125, 0.9495 and 0.9619, respectively. The best combination of parameters WT + ∆YMf was the best over-all predictor with an area under the ROC curve of 0.9951. Conclusion Computational modeling and material stiffness parameters may be used as a potential tool to suggest if a patient had infarction based on echo data. Large-scale clinical studies are needed to validate these preliminary findings.
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Affiliation(s)
- Longling Fan
- Department of Mathematics, Southeast University, Nanjing, 210096, China
| | - Jing Yao
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Chun Yang
- Network Technology Research Institute, China United Network Communications Co., Ltd., Beijing, 100048, China.,Mathematical Sciences Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA, 01609, USA
| | - Zheyang Wu
- Mathematical Sciences Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA, 01609, USA
| | - Di Xu
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Dalin Tang
- Department of Mathematics, Southeast University, Nanjing, 210096, China. .,Mathematical Sciences Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA, 01609, USA.
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14
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Fan L, Yao J, Yang C, Xu D, Tang D. Modeling Active Contraction and Relaxation of Left Ventricle Using Different Zero-load Diastole and Systole Geometries for Better Material Parameter Estimation and Stress/Strain Calculations. MOLECULAR & CELLULAR BIOMECHANICS : MCB 2016; 13:33-55. [PMID: 29399004 DOI: 10.3970/mcb.2016.013.044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Modeling ventricle active contraction based on in vivo data is extremely challenging because of complex ventricle geometry, dynamic heart motion and active contraction where the reference geometry (zero-stress geometry) changes constantly. A new modeling approach using different diastole and systole zero-load geometries was introduced to handle the changing zero-load geometries for more accurate stress/strain calculations. Echo image data were acquired from 5 patients with infarction (Infarct Group) and 10 without (Non-Infarcted Group). Echo-based computational two-layer left ventricle models using one zero-load geometry (1G) and two zero-load geometries (2G) were constructed. Material parameter values in Mooney-Rivlin models were adjusted to match echo volume data. Effective Young's moduli (YM) were calculated for easy comparison. For diastole phase, begin-filling (BF) mean YM value in the fiber direction (YMf) was 738% higher than its end-diastole (ED) value (645.39 kPa vs. 76.97 kPa, p=3.38E-06). For systole phase, end-systole (ES) YMf was 903% higher than its begin-ejection (BE) value (1025.10 kPa vs. 102.11 kPa, p=6.10E-05). Comparing systolic and diastolic material properties, ES YMf was 59% higher than its BF value (1025.10 kPa vs. 645.39 kPa. p=0.0002). BE mean stress value was 514% higher than its ED value (299.69 kPa vs. 48.81 kPa, p=3.39E-06), while BE mean strain value was 31.5% higher than its ED value (0.9417 vs. 0.7162, p=0.004). Similarly, ES mean stress value was 562% higher than its BF value (19.74 kPa vs. 2.98 kPa, p=6.22E-05), and ES mean strain value was 264% higher than its BF value (0.1985 vs. 0.0546, p=3.42E-06). 2G models improved over 1G model limitations and may provide better material parameter estimation and stress/strain calculations.
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Affiliation(s)
- Longling Fan
- Department of Mathematics, Southeast University, Nanjing, 210096, China
| | - Jing Yao
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China
| | - Chun Yang
- Network Technology Research Institute, China United Network Communications Co., Ltd., Beijing, 100048, China
| | - Di Xu
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China
| | - Dalin Tang
- Department of Mathematics, Southeast University, Nanjing, 210096, China.,Mathematical Sciences Department, Worcester Polytechnic Institute, MA 01609 USA
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15
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Biomechanical properties and microstructure of human ventricular myocardium. Acta Biomater 2015; 24:172-92. [PMID: 26141152 DOI: 10.1016/j.actbio.2015.06.031] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 05/12/2015] [Accepted: 06/24/2015] [Indexed: 11/23/2022]
Abstract
In the multidisciplinary field of heart research it is of utmost importance to identify accurate myocardium material properties for the description of phenomena such as mechano-electric feedback or heart wall thickening. A rationally-based material model is required to understand the highly nonlinear mechanics of complex structures such as the passive myocardium under different loading conditions. Unfortunately, to date there are no experimental data of human heart tissues available to estimate material parameters and to develop adequate material models. This study aimed to determine biaxial extension and triaxial shear properties and the underlying microstructure of the passive human ventricular myocardium. Using new state-of-the-art equipment, planar biaxial extension tests were performed to determine the biaxial extension properties of the passive ventricular human myocardium. Shear properties of the myocardium were examined by triaxial simple shear tests performed on small cubic specimens excised from an adjacent region of the biaxial extension specimens. The three-dimensional microstructure was investigated through second-harmonic generation (SHG) microscopy on optically cleared tissues, which emphasized the 3D orientation and dispersion of the myofibers and adjacent collagen fabrics. The results suggest that the passive human LV myocardium under quasi-static and dynamic multiaxial loadings is a nonlinear, anisotropic (orthotropic), viscoelastic and history-dependent soft biological material undergoing large deformations. Material properties of the tissue components along local microstructural axes drive the nonlinear and orthotropic features of the myocardium. SHG microscopy investigation revealed detailed information about the myocardial microstructure due to its high resolution. It enabled the identification of structural parameters such as the fiber and the sheet orientations and corresponding dispersions. With this complete set of material data, a sophisticated material model and associated material parameters can be defined for a better description of the biomechanical response of the ventricular myocardium in humans. Such a model will lead to more accurate computational simulations to better understand the fundamental underlying ventricular mechanics, a step needed in the improvement of medical treatment of heart diseases. STATEMENT OF SIGNIFICANCE Unfortunately, to date there are no experimental data of human heart tissues available for material parameter estimation and the development of adequate material models. In this manuscript novel biaxial tensile and shear test data at different specimen orientations are presented, which allowed to adequately capture the direction-dependent material response. With these complete sets of mechanical data, combined with their underlying microstructural data (also presented herein), sophisticated material models and associated material parameters can be defined for the description of the mechanical behavior of the ventricular myocardium in humans. Such models will lead to accurate computational simulations to better understand the fundamental underlying ventricular mechanics, a step needed in the improvement of medical treatment of heart diseases.
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16
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Fan L, Yao J, Yang C, Tang D, Xu D. Infarcted Left Ventricles Have Stiffer Material Properties and Lower Stiffness Variation: Three-Dimensional Echo-Based Modeling to Quantify In Vivo Ventricle Material Properties. J Biomech Eng 2015; 137:081005. [PMID: 25994130 DOI: 10.1115/1.4030668] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Indexed: 11/08/2022]
Abstract
Methods to quantify ventricle material properties noninvasively using in vivo data are of great important in clinical applications. An ultrasound echo-based computational modeling approach was proposed to quantify left ventricle (LV) material properties, curvature, and stress/strain conditions and find differences between normal LV and LV with infarct. Echo image data were acquired from five patients with myocardial infarction (I-Group) and five healthy volunteers as control (H-Group). Finite element models were constructed to obtain ventricle stress and strain conditions. Material stiffening and softening were used to model ventricle active contraction and relaxation. Systolic and diastolic material parameter values were obtained by adjusting the models to match echo volume data. Young's modulus (YM) value was obtained for each material stress-strain curve for easy comparison. LV wall thickness, circumferential and longitudinal curvatures (C- and L-curvature), material parameter values, and stress/strain values were recorded for analysis. Using the mean value of H-Group as the base value, at end-diastole, I-Group mean YM value for the fiber direction stress-strain curve was 54% stiffer than that of H-Group (136.24 kPa versus 88.68 kPa). At end-systole, the mean YM values from the two groups were similar (175.84 kPa versus 200.2 kPa). More interestingly, H-Group end-systole mean YM was 126% higher that its end-diastole value, while I-Group end-systole mean YM was only 29% higher that its end-diastole value. This indicated that H-Group had much greater systole-diastole material stiffness variations. At beginning-of-ejection (BE), LV ejection fraction (LVEF) showed positive correlation with C-curvature, stress, and strain, and negative correlation with LV volume, respectively. At beginning-of-filling (BF), LVEF showed positive correlation with C-curvature and strain, but negative correlation with stress and LV volume, respectively. Using averaged values of two groups at BE, I-Group stress, strain, and wall thickness were 32%, 29%, and 18% lower (thinner), respectively, compared to those of H-Group. L-curvature from I-Group was 61% higher than that from H-Group. Difference in C-curvature between the two groups was not statistically significant. Our results indicated that our modeling approach has the potential to determine in vivo ventricle material properties, which in turn could lead to methods to infer presence of infarct from LV contractibility and material stiffness variations. Quantitative differences in LV volume, curvatures, stress, strain, and wall thickness between the two groups were provided.
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17
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Michaelides M, Georgiadou S, Constantinides C. In vivo epicardial force and strain characterisation in normal and MLP-knockout murine hearts. Physiol Meas 2015; 36:1573-90. [PMID: 26057415 DOI: 10.1088/0967-3334/36/7/1573] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The study's objective is to quantify in vivo epicardial force and strain in the normal and transgenic myocardium using microsensors.Male mice (n = 39), including C57BL/6 (n = 26), 129/Sv (n = 5), wild-type (WT) C57 × 129Sv (n = 5), and muscle LIM protein (MLP) knock-out (n = 3), were studied under 1.5% isoflurane anaesthesia. Microsurgery allowed the placement of two piezoelectric crystals at longitudinal epicardial loci at the basal, middle, and apical LV regions, and the independent (and/or concurrent) placement of a cantilever force sensor. The findings demonstrate longitudinal contractile and relaxation strains that ranged between 4.8-9.3% in the basal, middle, and apical regions of C57BL/6 mice, and in the mid-ventricular regions of 129/Sv, WT, and MLP mice. Measured forces ranged between 3.1-8.9 mN. The technique's feasibility is also demonstrated in normal mice following afterload, occlusion-reperfusion challenges.Furthermore, the total mid-ventricular forces developed in MLP mice were significantly reduced compared to the WT controls (5.9 ± 0.4 versus 8.9 ± 0.2 mN, p < 0.0001), possibly owing to the fibrotic and stiffer myocardium. No significant strain differences were noted between WT and MLP mice.The possibility of quantifying in vivo force and strain from the normal murine heart is demonstrated with a potential usefulness in the characterisation of transgenic and diseased mice, where regional myocardial function may be significantly altered.
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Affiliation(s)
- M Michaelides
- Department of Mechanical and Manufacturing Engineering, School of Engineering, University of Cyprus, Nicosia, Cyprus. Lecturer, Department of Sport and Exercise Science, UCLan Cyprus, University Avenue 12-14, Pyla 7080, Cyprus
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18
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Sohal M, Duckett SG, Zhuang X, Shi W, Ginks M, Shetty A, Sammut E, Kozerke S, Niederer S, Smith N, Ourselin S, Rinaldi CA, Rueckert D, Carr-White G, Razavi R. A prospective evaluation of cardiovascular magnetic resonance measures of dyssynchrony in the prediction of response to cardiac resynchronization therapy. J Cardiovasc Magn Reson 2014; 16:58. [PMID: 25084814 PMCID: PMC4422256 DOI: 10.1186/s12968-014-0058-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 07/18/2014] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND Many patients with electrical dyssynchrony who undergo cardiac resynchronization therapy (CRT) do not obtain substantial benefit. Assessing mechanical dyssynchrony may improve patient selection. Results from studies using echocardiographic imaging to measure dyssynchrony have ultimately proved disappointing. We sought to evaluate cardiac motion in patients with heart failure and electrical dyssynchrony using cardiovascular magnetic resonance (CMR). We developed a framework for comparing measures of myocardial mechanics and evaluated how well they predicted response to CRT. METHODS CMR was performed at 1.5 Tesla prior to CRT. Steady-state free precession (SSFP) cine images and complementary modulation of magnetization (CSPAMM) tagged cine images were acquired. Images were processed using a novel framework to extract regional ventricular volume-change, thickening and deformation fields (strain). A systolic dyssynchrony index (SDI) for all parameters within a 16-segment model of the ventricle was computed with high SDI denoting more dyssynchrony. Once identified, the optimal measure was applied to a second patient population to determine its utility as a predictor of CRT response compared to current accepted predictors (QRS duration, LBBB morphology and scar burden). RESULTS Forty-four patients were recruited in the first phase (91% male, 63.3 ± 14.1 years; 80% NYHA class III) with mean QRSd 154 ± 24 ms. Twenty-one out of 44 (48%) patients showed reverse remodelling (RR) with a decrease in end systolic volume (ESV) ≥ 15% at 6 months. Volume-change SDI was the strongest predictor of RR (PR 5.67; 95% CI 1.95-16.5; P = 0.003). SDI derived from myocardial strain was least predictive. Volume-change SDI was applied as a predictor of RR to a second population of 50 patients (70% male, mean age 68.6 ± 12.2 years, 76% NYHA class III) with mean QRSd 146 ± 21 ms. When compared to QRSd, LBBB morphology and scar burden, volume-change SDI was the only statistically significant predictor of RR in this group. CONCLUSION A systolic dyssynchrony index derived from volume-change is a highly reproducible measurement that can be derived from routinely acquired SSFP cine images and predicts RR following CRT whilst an SDI of regional strain does not.
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Affiliation(s)
- Manav Sohal
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
- The Department of Cardiology, Guy's and St Thomas' NHS Foundation Trust, London, UK.
- Division of Imaging Sciences, The Rayne Institute, 4th Floor, Lambeth Wing, St Thomas' Hospital, London, SE1 7EH, UK.
| | - Simon G Duckett
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Xiahai Zhuang
- Centre for Medical Image Computing, University College London, London, UK.
| | - Wenzhe Shi
- Biomedical Image Analysis Group, Department of Computing, Imperial College London, London, UK.
| | - Matthew Ginks
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Anoop Shetty
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
- The Department of Cardiology, Guy's and St Thomas' NHS Foundation Trust, London, UK.
| | - Eva Sammut
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Sebastian Kozerke
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Steven Niederer
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Nic Smith
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
| | - Sebastien Ourselin
- Centre for Medical Image Computing, University College London, London, UK.
| | - Christopher Aldo Rinaldi
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
- The Department of Cardiology, Guy's and St Thomas' NHS Foundation Trust, London, UK.
| | - Daniel Rueckert
- Biomedical Image Analysis Group, Department of Computing, Imperial College London, London, UK.
| | - Gerald Carr-White
- The Department of Cardiology, Guy's and St Thomas' NHS Foundation Trust, London, UK.
| | - Reza Razavi
- Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, UK.
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Howard EJ, Kerckhoffs RCP, Vincent KP, Krishnamurthy A, Villongco CT, Mulligan LJ, McCulloch AD, Omens JH. Myofiber prestretch magnitude determines regional systolic function during ectopic activation in the tachycardia-induced failing canine heart. Am J Physiol Heart Circ Physiol 2013; 305:H192-202. [PMID: 23666676 PMCID: PMC3726954 DOI: 10.1152/ajpheart.00186.2012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 05/09/2013] [Indexed: 11/22/2022]
Abstract
Electrical dyssynchrony leads to prestretch in late-activated regions and alters the sequence of mechanical contraction, although prestretch and its mechanisms are not well defined in the failing heart. We hypothesized that in heart failure, fiber prestretch magnitude increases with the amount of early-activated tissue and results in increased end-systolic strains, possibly due to length-dependent muscle properties. In five failing dog hearts with scars, three-dimensional strains were measured at the anterolateral left ventricle (LV). Prestretch magnitude was varied via ventricular pacing at increasing distances from the measurement site and was found to increase with activation time at various wall depths. At the subepicardium, prestretch magnitude positively correlated with the amount of early-activated tissue. At the subendocardium, local end-systolic strains (fiber shortening, radial wall thickening) increased proportionally to prestretch magnitude, resulting in greater mean strain values in late-activated compared with early-activated tissue. Increased fiber strains at end systole were accompanied by increases in preejection fiber strain, shortening duration, and the onset of fiber relengthening, which were all positively correlated with local activation time. In a dog-specific computational failing heart model, removal of length and velocity dependence on active fiber stress generation, both separately and together, alter the correlations between local electrical activation time and timing of fiber strains but do not primarily account for these relationships.
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Affiliation(s)
- Elliot J Howard
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093-0613, USA
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20
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Fomovsky GM, Clark SA, Parker KM, Ailawadi G, Holmes JW. Anisotropic reinforcement of acute anteroapical infarcts improves pump function. Circ Heart Fail 2012; 5:515-22. [PMID: 22665716 DOI: 10.1161/circheartfailure.111.965731] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND We hypothesize that a therapy that improves left ventricular (LV) pump function early after infarction should decrease the need for compensation through sympathetic activation and dilation, thereby reducing the risk of developing heart failure. The mechanical properties of healing myocardial infarcts are an important determinant of LV function, yet improving function by altering infarct properties has proven unexpectedly difficult. Using a computational model, we recently predicted that stiffening a large anterior infarct anisotropically (in only one direction) would improve LV function, whereas isotropic stiffening, the focus of previous studies and therapies, would not. The goal of this study was to test the novel strategy of anisotropic infarct reinforcement. METHODS AND RESULTS We tested the effects of anisotropic infarct reinforcement in 10 open-chest dogs with large anteroapical infarcts that depressed LV pump function. We measured regional mechanics, LV volumes, and cardiac output at a range of preloads at baseline, 45 minutes after coronary ligation (ischemia), and 30 minutes later, after surgical reinforcement in the longitudinal direction (anisotropic). Ischemia shifted the end-systolic pressure-volume relationship and cardiac output curves rightward, decreasing cardiac output at matched end-diastolic pressure by 44%. Anisotropic reinforcement significantly improved systolic function without impairing diastolic function, recovering half the deficit in overall LV function. CONCLUSIONS We conclude that anisotropic reinforcement is a promising new approach to improving LV function after a large myocardial infarction.
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Affiliation(s)
- Gregory M Fomovsky
- Departments of Biomedical Engineering, Medicine, and Surgery and the Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908, USA
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21
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Rossi S, Ruiz-Baier R, Pavarino LF, Quarteroni A. Orthotropic active strain models for the numerical simulation of cardiac biomechanics. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2012; 28:761-788. [PMID: 25364850 DOI: 10.1002/cnm.2473] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Accepted: 01/17/2012] [Indexed: 06/04/2023]
Abstract
A model for the active deformation of cardiac tissue considering orthotropic constitutive laws is introduced and studied. In particular, the passive mechanical properties of the myocardium are described by the Holzapfel-Ogden relation, whereas the activation model is based on the concept of active strain. There, an incompatible intermediate configuration is considered, which entails a multiplicative decomposition between active and passive deformation gradients. The underlying Euler-Lagrange equations for minimizing the total energy are written in terms of these deformation factors, where the active part is assumed to depend, at the cell level, on the electrodynamics and on the specific orientation of the cardiomyocytes. The active strain formulation is compared with the classical active stress model from both numerical and modeling perspectives. The well-posedness of the linear system derived from a generic Newton iteration of the original problem is analyzed, and different mechanical activation functions are considered. Taylor-Hood and MINI finite elements are used in the discretization of the overall mechanical problem. The results of several numerical experiments show that the proposed formulation is mathematically consistent and is able to represent the main features of the phenomenon, while allowing savings in computational costs.
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Affiliation(s)
- Simone Rossi
- CMCS-MATHICSE-SB, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; Departamento de Matemática, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
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Tsamis A, Cheng A, Nguyen TC, Langer F, Miller DC, Kuhl E. Kinematics of cardiac growth: in vivo characterization of growth tensors and strains. J Mech Behav Biomed Mater 2012; 8:165-77. [PMID: 22402163 PMCID: PMC3298662 DOI: 10.1016/j.jmbbm.2011.12.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2011] [Revised: 11/29/2011] [Accepted: 12/16/2011] [Indexed: 12/22/2022]
Abstract
Progressive growth and remodeling of the left ventricle are part of the natural history of chronic heart failure and strong clinical indicators for survival. Accompanied by changes in cardiac form and function, they manifest themselves in alterations of cardiac strains, fiber stretches, and muscle volume. Recent attempts to shed light on the mechanistic origin of heart failure utilize continuum theories of growth to predict the maladaptation of the heart in response to pressure or volume overload. However, despite a general consensus on the representation of growth through a second order tensor, the precise format of this growth tensor remains unknown. Here we show that infarct-induced cardiac dilation is associated with a chronic longitudinal growth, accompanied by a chronic thinning of the ventricular wall. In controlled in vivo experiments throughout a period of seven weeks, we found that the lateral left ventricular wall adjacent to the infarct grows longitudinally by more than 10%, thins by more than 25%, lengthens in fiber direction by more than 5%, and decreases its volume by more than 15%. Our results illustrate how a local loss of blood supply induces chronic alterations in structure and function in adjacent regions of the ventricular wall. We anticipate our findings to be the starting point for a series of in vivo studies to calibrate and validate constitutive models for cardiac growth. Ultimately, these models could be useful to guide the design of novel therapies, which allow us to control the progression of heart failure.
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Abstract
The right ventricular apex (RVA) is a potential hot spot for development of cardiac rhythm anomalies. Many conditions, including arrhythmogenic right ventricular cardiomyopathy and Brugada's syndrome affect the RVA, and further, the RVA remains an incompletely characterized pacing region. Whether there are structural reasons underlying these conduction properties remains unsettled. In the current study, we characterize the mechanical strains and structural attributes of the right ventricular wall, and test the hypothesis that the right ventricular apex experiences heterogeneous strain distributions and altered fiber organization, and is thus susceptible to conduction alterations. Electromechanical wave imaging (EWI), or elastography, of hearts was used to quantify mechanical strains occurring through a cardiac cycle. Histological and immunofluorescence imaging techniques were used to examine cardiac wall structure and arrangement of junctional proteins. Right ventricular mechanical strains were elevated and sustained throughout systole, compared to the left ventricle and septum. Heterogeneous strain distributions, myocardial fiber disarray, and altered junctional protein localization occured at the RVA. Disarray and altered strain distributions suggest decreased structural strength at the right ventricular apex in particular and increased mechanical impositions in the right ventricle, respectively. Thus, these data demonstrate why the right ventricular apex may be particularly vulnerable to conduction abnormalities.
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Itoh A, Stephens EH, Ennis DB, Carlhall CJ, Bothe W, Nguyen TC, Swanson JC, Miller DC, Ingels NB. Contribution of myocardium overlying the anterolateral papillary muscle to left ventricular deformation. Am J Physiol Heart Circ Physiol 2011; 302:H180-7. [PMID: 22037187 DOI: 10.1152/ajpheart.00687.2011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous studies of transmural left ventricular (LV) strains suggested that the myocardium overlying the papillary muscle displays decreased deformation relative to the anterior LV free wall or significant regional heterogeneity. These comparisons, however, were made using different hearts. We sought to extend these studies by examining three equatorial LV regions in the same heart during the same heartbeat. Therefore, deformation was analyzed from transmural beadsets placed in the equatorial LV myocardium overlying the anterolateral papillary muscle (PAP), as well as adjacent equatorial LV regions located more anteriorly (ANT) and laterally (LAT). We found that the magnitudes of LAT normal longitudinal and radial strains, as well as major principal strains, were less than ANT, while those of PAP were intermediate. Subepicardial and midwall myofiber angles of LAT, PAP, and ANT were not significantly different, but PAP subendocardial myofiber angles were significantly higher (more longitudinal as opposed to circumferential orientation). Subepicardial and midwall myofiber strains of ANT, PAP, and LAT were not significantly different, but PAP subendocardial myofiber strains were less. Transmural gradients in circumferential and radial normal strains, and major principal strains, were observed in each region. The two main findings of this study were as follows: 1) PAP strains are largely consistent with adjacent LV equatorial free wall regions, and 2) there is a gradient of strains across the anterolateral equatorial left ventricle despite similarities in myofiber angles and strains. These findings point to graduated equatorial LV heterogeneity and suggest that regional differences in myofiber coupling may constitute the basis for such heterogeneity.
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Affiliation(s)
- Akinobu Itoh
- Department of Cardiothoracic Surgery, Stanford University School of Medicine, California, USA
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Howard EJ, Covell JW, Mulligan LJ, McCulloch AD, Omens JH, Kerckhoffs RCP. Improvement in pump function with endocardial biventricular pacing increases with activation time at the left ventricular pacing site in failing canine hearts. Am J Physiol Heart Circ Physiol 2011; 301:H1447-55. [PMID: 21784986 DOI: 10.1152/ajpheart.00295.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently, attention has been focused on comparing left ventricular (LV) endocardial (ENDO) with epicardial (EPI) pacing for cardiac resynchronization therapy. However, the effects of ENDO and EPI lead placement at multiple sites have not been studied in failing hearts. We hypothesized that differences in the improvement of ventricular function due to ENDO vs. EPI pacing in dyssynchronous (DYSS) heart failure may depend on the position of the LV lead in relation to the original activation pattern. In six nonfailing and six failing dogs, electrical DYSS was created by atrioventricular sequential pacing of the right ventricular apex. ENDO was compared with EPI biventricular pacing at five LV sites. In failing hearts, increases in the maximum rate of LV pressure change (dP/dt; r = 0.64), ejection fraction (r = 0.49), and minimum dP/dt (r = 0.51), relative to DYSS, were positively correlated (P < 0.01) with activation time at the LV pacing site during ENDO but not EPI pacing. ENDO pacing at sites with longer activation delays led to greater improvements in hemodynamic parameters and was associated with an overall reduction in electrical DYSS compared with EPI pacing (P < 0.05). These findings were qualitatively similar for nonfailing hearts. Improvement in hemodynamic function increased with activation time at the LV pacing site during ENDO but not EPI pacing. At the anterolateral wall, end-systolic transmural function was greater with local ENDO compared with EPI pacing. ENDO pacing and intrinsic activation delay may have important implications for management of DYSS heart failure.
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Affiliation(s)
- Elliot J Howard
- Department of Bioengineering, University of California San Diego, La Jolla, California 92093-0613, USA
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Tang D, Yang C, Geva T, Gaudette G, del Nido PJ. Multi-Physics MRI-Based Two-Layer Fluid-Structure Interaction Anisotropic Models of Human Right and Left Ventricles with Different Patch Materials: Cardiac Function Assessment and Mechanical Stress Analysis. COMPUTERS & STRUCTURES 2011; 89:1059-1068. [PMID: 21765559 PMCID: PMC3134331 DOI: 10.1016/j.compstruc.2010.12.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Multi-physics right and left ventricle (RV/LV) fluid-structure interaction (FSI) models were introduced to perform mechanical stress analysis and evaluate the effect of patch materials on RV function. The FSI models included three different patch materials (Dacron scaffold, treated pericardium, and contracting myocardium), two-layer construction, fiber orientation, and active anisotropic material properties. The models were constructed based on cardiac magnetic resonance (CMR) images acquired from a patient with severe RV dilatation and solved by ADINA. Our results indicate that the patch model with contracting myocardium leads to decreased stress level in the patch area, improved RV function and patch area contractility.
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Affiliation(s)
- Dalin Tang
- Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609
| | - Chun Yang
- Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609
- School of Mathematics, Beijing Normal University, Beijing, China
| | - Tal Geva
- Dept of Cardiology, Children’s Hospital Boston, Dept of Pediatrics, Harvard Medical School, Boston, MA 02115 USA
| | - Glenn Gaudette
- Dept of Biomedical Engineering, Worcester Polytechnic Institute, MA 01609, USA
| | - Pedro J. del Nido
- Dept. of Cardiac Surgery, Children’s Hospital Boston, Dept of Surgery, Harvard Medical School, Boston, MA 02115 USA
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Tsamis A, Bothe W, Kvitting JPE, Swanson JC, Miller DC, Kuhl E. Active contraction of cardiac muscle: in vivo characterization of mechanical activation sequences in the beating heart. J Mech Behav Biomed Mater 2011; 4:1167-76. [PMID: 21783125 DOI: 10.1016/j.jmbbm.2011.03.027] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2011] [Revised: 03/22/2011] [Accepted: 03/29/2011] [Indexed: 11/27/2022]
Abstract
Progressive alterations in cardiac wall strains are a classic hallmark of chronic heart failure. Accordingly, the objectives of this study are to establish a baseline characterization of cardiac strains throughout the cardiac cycle, to quantify temporal, regional, and transmural variations of active fiber contraction, and to identify pathways of mechanical activation in the healthy beating heart. To this end, we insert two sets of twelve radiopaque beads into the heart muscle of nine sheep; one in the anterior-basal and one in the lateral-equatorial left ventricular wall. During three consecutive heartbeats, we record the bead coordinates via biplane videofluoroscopy. From the resulting four-dimensional data sets, we calculate the temporally and transmurally varying Green-Lagrange strains in the anterior and lateral wall. To quantify active contraction, we project the strains onto the local muscle fiber directions. We observe that mechanical activation is initiated at the endocardium slightly after end diastole and progresses transmurally outward, reaching the epicardium slightly before end systole. Accordingly, fibers near the outer wall are in contraction for approximately half of the cardiac cycle while fibers near the inner wall are in contraction almost throughout the entire cardiac cycle. In summary, cardiac wall strains display significant temporal, regional, and transmural variations. Quantifying wall strain profiles might be of particular clinical significance when characterizing stages of left ventricular remodeling, but also of engineering relevance when designing new biomaterials of similar structure and function.
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Affiliation(s)
- Alkiviadis Tsamis
- Department of Mechanical Engineering, 496 Lomita Mall, Stanford, CA-94305, USA
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Veress AI, Segars WP, Tsui BMW, Gullberg GT. Incorporation of a left ventricle finite element model defining infarction into the XCAT imaging phantom. IEEE TRANSACTIONS ON MEDICAL IMAGING 2011; 30:915-927. [PMID: 21041157 PMCID: PMC3097415 DOI: 10.1109/tmi.2010.2089801] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The 4D extended cardiac-torso (XCAT) phantom was developed to provide a realistic and flexible model of the human anatomy and cardiac and respiratory motions for use in medical imaging research. A prior limitation to the phantom was that it did not accurately simulate altered functions of the heart that result from cardiac pathologies such as coronary artery disease (CAD). We overcame this limitation in a previous study by combining the phantom with a finite-element (FE) mechanical model of the left ventricle (LV) capable of more realistically simulating regional defects caused by ischemia. In the present work, we extend this model giving it the ability to accurately simulate motion abnormalities caused by myocardial infarction (MI), a far more complex situation in terms of altered mechanics compared with the modeling of acute ischemia. The FE model geometry is based on high resolution CT images of a normal male subject. An anterior region was defined as infarcted and the material properties and fiber distribution were altered, according to the bio-physiological properties of two types of infarction, i.e., fibrous and remodeled infarction (30% thinner wall than fibrous case). Compared with the original, surface-based 4D beating heart model of the XCAT, where regional abnormalities are modeled by simply scaling down the motion in those regions, the FE model was found to provide a more accurate representation of the abnormal motion of the LV due to the effects of fibrous infarction as well as depicting the motion of remodeled infarction. In particular, the FE models allow for the accurate depiction of dyskinetic motion. The average circumferential strain results were found to be consistent with measured dyskinetic experimental results. Combined with the 4D XCAT phantom, the FE model can be used to produce realistic multimodality sets of imaging data from a variety of patients in which the normal or abnormal cardiac function is accurately represented.
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Affiliation(s)
| | - W. Paul Segars
- Department of Radiology, Duke University, Durham, NC 27705 USA
| | | | - Grant T. Gullberg
- E. O. Lawrence Berkeley National Laboratory, Life Science Division, Berkeley, CA 94720 USA
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Tang D, Yang C, Geva T, del Nido PJ. Image-Based Patient-Specific Ventricle Models with Fluid-Structure Interaction for Cardiac Function Assessment and Surgical Design Optimization. PROGRESS IN PEDIATRIC CARDIOLOGY 2010; 30:51-62. [PMID: 21344066 PMCID: PMC3041970 DOI: 10.1016/j.ppedcard.2010.09.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recent advances in medical imaging technology and computational modeling techniques are making it possible that patient-specific computational ventricle models be constructed and used to test surgical hypotheses and replace empirical and often risky clinical experimentation to examine the efficiency and suitability of various reconstructive procedures in diseased hearts. In this paper, we provide a brief review on recent development in ventricle modeling and its potential application in surgical planning and management of tetralogy of Fallot (ToF) patients. Aspects of data acquisition, model selection and construction, tissue material properties, ventricle layer structure and tissue fiber orientations, pressure condition, model validation and virtual surgery procedures (changing patient-specific ventricle data and perform computer simulation) were reviewed. Results from a case study using patient-specific cardiac magnetic resonance (CMR) imaging and right/left ventricle and patch (RV/LV/Patch) combination model with fluid-structure interactions (FSI) were reported. The models were used to evaluate and optimize human pulmonary valve replacement/insertion (PVR) surgical procedure and patch design and test a surgical hypothesis that PVR with small patch and aggressive scar tissue trimming in PVR surgery may lead to improved recovery of RV function and reduced stress/strain conditions in the patch area.
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Affiliation(s)
- Dalin Tang
- Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609
| | - Chun Yang
- Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609
- School of Mathematics, Beijing Normal University, Beijing, China
| | - Tal Geva
- Dept of Cardiology, Children's Hospital Boston, Dept of Pediatrics, Harvard Medical School, Boston, MA 02115 USA
| | - Pedro J. del Nido
- Dept. of Cardiac Surgery, Children’s Hospital Boston, Dept of Surgery, Harvard Medical School, Boston, MA 02115 USA
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Model-based design of mechanical therapies for myocardial infarction. J Cardiovasc Transl Res 2010; 4:82-91. [PMID: 21088945 DOI: 10.1007/s12265-010-9241-3] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Accepted: 11/03/2010] [Indexed: 10/18/2022]
Abstract
The mechanical properties of healing myocardial infarcts are a critical determinant of pump function and the transition to heart failure. Recent reports suggest that modifying infarct mechanical properties can improve function and limit ventricular remodeling. However, little attempt has been made to identify the specific infarct material properties that would optimize left ventricular (LV) function. We utilized a finite-element model of a large anteroapical infarct in a dog heart to explore a wide range of infarct mechanical properties. Isotropic stiffening of the infarct reduced end-diastolic (EDV) and end-systolic (ESV) volumes, improved LV contractility, but had little effect on stroke volume. A highly anisotropic infarct, with high longitudinal stiffness but low circumferential stiffness coefficients, produced the best stroke volume by increasing diastolic filling, without affecting contractility or ESV. Simulated infarcts in two different locations displayed different transmural strain patterns. Our results suggest that there is a general trade-off between acutely reducing LV size and acutely improving LV pump function, that isotropically stiffening the infarct is not the only option of potential therapeutic interest, and that customizing therapies for different infarct locations may be important. Our model results should provide guidance for design and development of therapies to improve LV function by modifying infarct mechanical properties.
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Niederer SA, Plank G, Chinchapatnam P, Ginks M, Lamata P, Rhode KS, Rinaldi CA, Razavi R, Smith NP. Length-dependent tension in the failing heart and the efficacy of cardiac resynchronization therapy. Cardiovasc Res 2010; 89:336-43. [PMID: 20952413 DOI: 10.1093/cvr/cvq318] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Cardiac resynchronization therapy (CRT) has emerged as one of the few effective and safe treatments for heart failure. However, identifying patients that will benefit from CRT remains controversial. The dependence of CRT efficacy on organ and cellular scale mechanisms was investigated in a patient-specific computer model to identify novel patient selection criteria. METHODS AND RESULTS A biophysically based patient-specific coupled electromechanics heart model has been developed which links the cellular and sub-cellular mechanisms which regulate cardiac function to the whole organ function observed clinically before and after CRT. A sensitivity analysis of the model identified lack of length dependence of tension regulation within the sarcomere as a significant contributor to the efficacy of CRT. Further simulation analysis demonstrated that in the whole heart, length-dependent tension development is key not only for the beat-to-beat regulation of stroke volume (Frank-Starling mechanism), but also the homogenization of tension development and strain. CONCLUSIONS In individuals with effective Frank-Starling mechanism, the length dependence of tension facilitates the homogenization of stress and strain. This can result in synchronous contraction despite asynchronous electrical activation. In these individuals, synchronizing electrical activation through CRT may have minimal benefit.
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Affiliation(s)
- Steven A Niederer
- Biomedical Engineering Department, The Rayne Institute, 4th Floor, Lambeth Wing, St Thomas' Hospital, London SE1 7EH, UK
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Kindberg K, Oom C, Ingels NB, Karlsson M. Strain-based estimation of time-dependent transmural myocardial architecture in the ovine heart. Biomech Model Mechanobiol 2010; 10:521-8. [PMID: 20821245 DOI: 10.1007/s10237-010-0252-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Accepted: 08/17/2010] [Indexed: 10/19/2022]
Abstract
Left ventricular myofibers are connected by an extensive extracellular collagen matrix to form myolaminar sheets. Histological cardiac tissue studies have previously observed a pleated transmural distribution of sheets in the ovine heart, alternating sign of the sheet angle from epicardium to endocardium. The present study investigated temporal variations in myocardial fiber and sheet architecture during the cardiac cycle. End-diastolic histological measurements made at subepicardium, midwall, and subendocardium at an anterior-basal and a lateral-equatorial region of the ovine heart, combined with transmural myocardial Lagrangian strains, showed that the sheet angle but not the fiber angle varied temporally throughout the cardiac cycle. The magnitude of the sheet angle decreased during systole at all transmural depths at the anterior-basal site and at midwall and subendocardium depths at the lateral-equatorial site, making the sheets more parallel to the radial axis. These results support a previously suggested accordion-like wall-thickening mechanism of the myocardial sheets.
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Affiliation(s)
- Katarina Kindberg
- Department of Management and Engineering, Linköping University, Linköping, Sweden.
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Kindberg K, Carlhäll C, Karlsson M, Nguyen TC, Cheng A, Langer F, Rodriguez F, Daughters GT, Miller DC, Ingels NB. Transmural strains in the ovine left ventricular lateral wall during diastolic filling. J Biomech Eng 2009; 131:061004. [PMID: 19449958 DOI: 10.1115/1.3118774] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Rapid early diastolic left ventricular (LV) filling requires a highly compliant chamber immediately after systole, allowing inflow at low driving pressures. The transmural LV deformations associated with such filling are not completely understood. We sought to characterize regional transmural LV strains during diastole, with focus on early filling, in ovine hearts at 1 week and 8 weeks after myocardial marker implantation. In seven normal sheep hearts, 13 radiopaque markers were inserted to silhouette the LV chamber and a transmural beadset was implanted into the lateral equatorial LV wall to measure transmural strains. Four-dimensional marker dynamics were obtained 1 week and 8 weeks thereafter with biplane videofluoroscopy in closed-chest, anesthetized animals. LV transmural strains in both cardiac and fiber-sheet coordinates were studied from filling onset to the end of early filling (EOEF, 100 ms after filling onset) and at end diastole. At the 8 week study, subepicardial circumferential strain (ECC) had reached its final value already at EOEF, while longitudinal and radial strains were nearly zero at this time. Subepicardial ECC and fiber relengthening (Eff) at EOEF were reduced to 1 compared with 8 weeks after surgery (ECC:0.02+/-0.01 to 0.08+/-0.02 and Eff:0.00+/-0.01 to 0.03+/-0.01, respectively, both P<0.05). Subepicardial ECC during early LV filling was associated primarily with fiber-normal and sheet-normal shears at the 1 week study, but to all three fiber-sheet shears and fiber relengthening at the 8 week study. These changes in LV subepicardial mechanics provide a possible mechanistic basis for regional myocardial lusitropic function, and may add to our understanding of LV myocardial diastolic dysfunction.
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Affiliation(s)
- K Kindberg
- Department of Management and Engineering, Linköping University, Linköping SE-581 83, Sweden
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Ashikaga H, van der Spoel TIG, Coppola BA, Omens JH. Transmural myocardial mechanics during isovolumic contraction. JACC Cardiovasc Imaging 2009; 2:202-11. [PMID: 19356557 DOI: 10.1016/j.jcmg.2008.11.009] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Revised: 10/20/2008] [Accepted: 11/11/2008] [Indexed: 11/30/2022]
Abstract
OBJECTIVES We sought to resolve the 3-dimensional transmural heterogeneity in myocardial mechanics observed during the isovolumic contraction (IC) phase. BACKGROUND Although myocardial deformation during IC is expected to be little, recent tissue Doppler imaging studies suggest dynamic myocardial motions during this phase with biphasic longitudinal tissue velocities in left ventricular (LV) long-axis views. A unifying understanding of myocardial mechanics that would account for these dynamic aspects of IC is lacking. METHODS We determined the time course of 3-dimensional finite strains in the anterior LV of 14 adult mongrel dogs in vivo during IC and ejection with biplane cineradiography of implanted transmural markers. Transmural fiber orientations were histologically measured in the heart tissue postmortem. The strain time course was determined in the subepicardial, midwall, and subendocardial layers referenced to the end-diastolic configuration. RESULTS During IC, there was circumferential stretch in the subepicardial layer, whereas circumferential shortening was observed in the midwall and the subendocardial layer. There was significant longitudinal shortening and wall thickening across the wall. Although longitudinal tissue velocity showed a biphasic profile; tissue deformation in the longitudinal as well as other directions was almost linear during IC. Subendocardial fibers shortened, whereas subepicardial fibers lengthened. During ejection, all strain components showed a significant change over time that was greater in magnitude than that of IC. Significant transmural gradient was observed in all normal strains. CONCLUSIONS IC is a dynamic phase characterized by deformation in circumferential, longitudinal, and radial directions. Tissue mechanics during IC, including fiber shortening, appear uninterrupted by rapid longitudinal motion created by mitral valve closure. This study is the first to report layer-dependent deformation of circumferential strain, which results from layer-dependent deformation of myofibers during IC. Complex myofiber mechanics provide the mechanism of brief clockwise LV rotation (untwisting) and significant wall thickening during IC within the isovolumic constraint.
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Affiliation(s)
- Hiroshi Ashikaga
- Department of Medicine and Bioengineering, University of California, San Diego, CA, USA.
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Blyakhman FA, Naidich AM, Kolchanova SG, Sokolov SY, Kremleva YV, Chestukhin VV. Validity of ejection fraction as a measure of myocardial functional state: impact of asynchrony. EUROPEAN JOURNAL OF ECHOCARDIOGRAPHY 2009; 10:613-8. [PMID: 19218567 DOI: 10.1093/ejechocard/jep010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AIMS The goal of this study was to test whether peculiarities of left ventricular (LV) regional function place limits on the validity of ejection fraction (EF) as a measure of the myocardial functional state. METHODS AND RESULTS Transthoracic and transoesophageal data from patients with a variety of cardiac conditions were used for analysis of LV regional function. The focus was on the effects of mechanical asynchrony. Ejection fraction was calculated on the basis of LV end-diastolic volume and end-systolic volume obtained by two different ways: (i) end-systolic volume as a whole; and (ii) the sum of all regional end-systolic volumes (which may occur at different times). The relative difference, D-EF, between EFs obtained by (i) and (ii) was taken as the 'merit' of EF. A value of zero is the highest merit. Irrespective of the examination method, we found that D-EF was always higher than zero, and that its value depended on the extent of mechanical asynchrony. CONCLUSIONS Ejection fraction is not the arithmetic average of regional EFs. An increase of asynchrony increases D-EF, i.e. it reduces the merit of EF as a measure of cardiac function.
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Affiliation(s)
- Felix A Blyakhman
- Department of Biomedical Physics, Ural State Medical Academy, 3 Repin Str., Ekaterinburg 620219, Russia.
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Zhong L, Su Y, Yeo SY, Tan RS, Ghista DN, Kassab G. Left ventricular regional wall curvedness and wall stress in patients with ischemic dilated cardiomyopathy. Am J Physiol Heart Circ Physiol 2009; 296:H573-84. [PMID: 19122166 DOI: 10.1152/ajpheart.00525.2008] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Geometric remodeling of the left ventricle (LV) after myocardial infarction is associated with changes in myocardial wall stress. The objective of this study was to determine the regional curvatures and wall stress based on three-dimensional (3-D) reconstructions of the LV using MRI. Ten patients with ischemic dilated cardiomyopathy (IDCM) and 10 normal subjects underwent MRI scan. The IDCM patients also underwent delayed gadolinium-enhancement imaging to delineate the extent of myocardial infarct. Regional curvedness, local radii of curvature, and wall thickness were calculated. The percent curvedness change between end diastole and end systole was also calculated. In normal heart, a short- and long-axis two-dimensional analysis showed a 41 +/- 11% and 45 +/- 12% increase of the mean of peak systolic wall stress between basal and apical sections, respectively. However, 3-D analysis showed no significant difference in peak systolic wall stress from basal and apical sections (P = 0.298, ANOVA). LV shape differed between IDCM patients and normal subjects in several ways: LV shape was more spherical (sphericity index = 0.62 +/- 0.08 vs. 0.52 +/- 0.06, P < 0.05), curvedness at end diastole (mean for 16 segments = 0.034 +/- 0.0056 vs. 0.040 +/- 0.0071 mm(-1), P < 0.001) and end systole (mean for 16 segments = 0.037 +/- 0.0068 vs. 0.067 +/- 0.020 mm(-1), P < 0.001) was affected by infarction, and peak systolic wall stress was significantly increased at each segment in IDCM patients. The 3-D quantification of regional wall stress by cardiac MRI provides more precise evaluation of cardiac mechanics. Identification of regional curvedness and wall stresses helps delineate the mechanisms of LV remodeling in IDCM and may help guide therapeutic LV restoration.
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Affiliation(s)
- Liang Zhong
- Deparment of Cardiology, National Heart Centre, Singapore
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38
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Tang D, Yang C, Geva T, Del Nido PJ. Patient-specific MRI-based 3D FSI RV/LV/patch models for pulmonary valve replacement surgery and patch optimization. J Biomech Eng 2008; 130:041010. [PMID: 18601452 DOI: 10.1115/1.2913339] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A patient-specific right/left ventricle and patch (RV/LV/patch) combination model with fluid-structure interactions (FSIs) was introduced to evaluate and optimize human pulmonary valve replacement/insertion (PVR) surgical procedure and patch design. Cardiac magnetic resonance (CMR) imaging studies were performed to acquire ventricle geometry, flow velocity, and flow rate for healthy volunteers and patients needing RV remodeling and PVR before and after scheduled surgeries. CMR-based RV/LV/patch FSI models were constructed to perform mechanical analysis and assess RV cardiac functions. Both pre- and postoperation CMR data were used to adjust and validate the model so that predicted RV volumes reached good agreement with CMR measurements (error <3%). Two RV/LV/patch models were made based on preoperation data to evaluate and compare two PVR surgical procedures: (i) conventional patch with little or no scar tissue trimming, and (ii) small patch with aggressive scar trimming and RV volume reduction. Our modeling results indicated that (a) patient-specific CMR-based computational modeling can provide accurate assessment of RV cardiac functions, and (b) PVR with a smaller patch and more aggressive scar removal led to reduced stress/strain conditions in the patch area and may lead to improved recovery of RV functions. More patient studies are needed to validate our findings.
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Affiliation(s)
- Dalin Tang
- Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609, USA.
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39
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Cheng A, Nguyen TC, Malinowski M, Daughters GT, Miller DC, Ingels NB. Heterogeneity of left ventricular wall thickening mechanisms. Circulation 2008; 118:713-21. [PMID: 18663088 DOI: 10.1161/circulationaha.107.744623] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Myocardial fibers are grouped into lamina (or sheets) 3 to 4 cells thick. Fiber shortening produces systolic left ventricular (LV) wall thickening primarily by laminar extension, thickening, and shear, but the regional variability and transmural distribution of these 3 mechanisms are incompletely understood. METHODS AND RESULTS Nine sheep had transmural radiopaque markers inserted into the anterior basal and lateral equatorial LV. Four-dimensional marker dynamics were studied with biplane videofluoroscopy to measure circumferential, longitudinal, and radial systolic strains in the epicardium, midwall, and endocardium. Fiber and sheet angles from quantitative histology allowed transformation of these strains into transmural contributions of sheet extension, thickening, and shear to systolic wall thickening. At all depths, systolic wall thickening in the anterior basal region was 1.6 to 1.9 times that in the lateral equatorial region. Interestingly, however, systolic fiber shortening was identical at each transmural depth in these regions. Endocardial anterior basal sheet thickening was >2 times greater than in the lateral equatorial region (epicardium, 0.16+/-0.15 versus 0.03+/-0.06; endocardium, 0.45+/-0.40 versus 0.17+/-0.09). Midwall sheet extension was >2 times that in the lateral wall (0.22+/-0.12 versus 0.09+/-0.06). Epicardial and midwall sheet shears in the anterior wall were approximately 2 times higher than in the lateral wall (epicardium, 0.14+/-0.07 versus 0.05+/-0.03; midwall, 0.21+/-0.12 versus 0.12+/-0.06). CONCLUSIONS These data demonstrate fundamentally different regional contributions of laminar mechanisms for amplifying fiber shortening to systolic wall thickening. Systolic fiber shortening was identical at each transmural depth in both the anterior and lateral LV sites. However, systolic wall thickening of the anterior site was much greater than that of the lateral site. Fiber shortening drives systolic wall thickening, but sheet dynamics and orientations are of great importance to systolic wall thickening. LV wall thickening and its clinical implications pivot on different wall thickening mechanisms in various LV regions. Attempts to implant healthy contractile cells into diseased hearts or to surgically manipulate LV geometry need to take into account not only cardiomyocyte contraction but also transmural LV intercellular architecture and geometry.
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Affiliation(s)
- Allen Cheng
- Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine, Stanford, CA, USA
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Pope AJ, Sands GB, Smaill BH, LeGrice IJ. Three-dimensional transmural organization of perimysial collagen in the heart. Am J Physiol Heart Circ Physiol 2008; 295:H1243-H1252. [PMID: 18641274 PMCID: PMC2544485 DOI: 10.1152/ajpheart.00484.2008] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
There is strong support for the view that the ventricular myocardium has a laminar organization in which myocytes are grouped into branching layers separated by cleavage planes. However, understanding of the extent and functional implications of this architecture has been limited by the lack of a systematic three-dimensional description of the organization of myocytes and associated perimysial collagen. We imaged myocytes and collagen across the left ventricular wall at high resolution in seven normal rat hearts using extended volume confocal microscopy. We developed novel reconstruction and segmentation techniques necessary for the quantitative analysis of three-dimensional myocyte and perimysial collagen organization. The results confirm that perimysial collagen has an ordered arrangement and that it defines a laminar organization. Perimysial collagen is composed of three distinct forms: extensive meshwork on laminar surfaces, convoluted fibers connecting adjacent layers, and longitudinal cords. While myolaminae are the principal form of structural organization throughout most of the wall, they are not seen in the subepicardium, where perimysial collagen is present only as longitudinal cords.
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Affiliation(s)
- Adèle J Pope
- Department of Physiology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
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41
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Sengupta PP, Krishnamoorthy VK, Korinek J, Narula J, Vannan MA, Lester SJ, Tajik JA, Seward JB, Khandheria BK, Belohlavek M. Left ventricular form and function revisited: applied translational science to cardiovascular ultrasound imaging. J Am Soc Echocardiogr 2007; 20:539-51. [PMID: 17485001 PMCID: PMC1951787 DOI: 10.1016/j.echo.2006.10.013] [Citation(s) in RCA: 228] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2006] [Indexed: 02/08/2023]
Abstract
Doppler tissue imaging (DTI) and DTI-derived strain imaging are robust physiologic tools used for the noninvasive assessment of regional myocardial function. As a result of high temporal and spatial resolution, regional function can be assessed for each phase of the cardiac cycle and within the transmural layers of the myocardial wall. Newer techniques that measure myocardial motion by speckle tracking in gray-scale images have overcome the angle dependence of DTI strain, allowing for measurement of 2-dimensional strain and cardiac rotation. DTI, DTI strain, and speckle tracking may provide unique information that deciphers the deformation sequence of complexly oriented myofibers in the left ventricular wall. The data are, however, limited. This review examines the structure and function of the left ventricle relative to the potential clinical application of DTI and speckle tracking in assessing the global mechanical sequence of the left ventricle in vivo.
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Affiliation(s)
- Partho P Sengupta
- Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA
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42
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Ashikaga H, Coppola BA, Hopenfeld B, Leifer ES, McVeigh ER, Omens JH. Transmural dispersion of myofiber mechanics: implications for electrical heterogeneity in vivo. J Am Coll Cardiol 2007; 49:909-16. [PMID: 17320750 PMCID: PMC2572715 DOI: 10.1016/j.jacc.2006.07.074] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Revised: 07/05/2006] [Accepted: 07/10/2006] [Indexed: 10/23/2022]
Abstract
OBJECTIVES We investigated whether transmural mechanics could yield insight into the transmural electrical sequence. BACKGROUND Although the concept of transmural dispersion of repolarization has helped explain a variety of arrhythmias, its presence in vivo is still disputable. METHODS We studied the time course of transmural myofiber mechanics in the anterior left ventricle of normal canines in vivo (n = 14) using transmural bead markers under biplane cineradiography. In 4 of these animals, plunge electrodes were placed in the myocardial tissue within the bead set to measure transmural electrical sequence. RESULTS The onset of myofiber shortening was earliest at endocardial layers and progressively delayed toward epicardial layers (p < 0.001), resulting in transmural dispersion of myofiber shortening of 39 ms. The onset of myofiber relaxation was earliest at epicardial layers and most delayed at subendocardial layers (p = 0.004), resulting in transmural dispersion of myofiber relaxation of 83 ms. There was no significant transmural gradient in electrical repolarization (p = NS). CONCLUSIONS Despite lack of evidence of significant transmural gradient in electrical repolarization in vivo, there is transmural dispersion of myofiber relaxation as well as shortening.
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Affiliation(s)
- Hiroshi Ashikaga
- Department of Medicine and Bioengineering, University of California, San Diego, La Jolla, California, USA.
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43
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Sengupta PP, Korinek J, Belohlavek M, Narula J, Vannan MA, Jahangir A, Khandheria BK. Left ventricular structure and function: basic science for cardiac imaging. J Am Coll Cardiol 2006; 48:1988-2001. [PMID: 17112989 DOI: 10.1016/j.jacc.2006.08.030] [Citation(s) in RCA: 325] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Revised: 08/29/2006] [Accepted: 08/30/2006] [Indexed: 12/11/2022]
Abstract
The myofiber geometry of the left ventricle (LV) changes gradually from a right-handed helix in the subendocardium to a left-handed helix in the subepicardium. In this review, we associate the LV myofiber architecture with emerging concepts of the electromechanical sequence in a beating heart. We discuss: 1) the morphogenesis and anatomical arrangement of muscle fibers in the adult LV; 2) the sequence of depolarization and repolarization; 3) the physiological inhomogeneity of transmural myocardial mechanics and the apex-to-base sequence of longitudinal and circumferential deformation; 4) the sequence of LV rotation; and 5) the link between LV deformation and the intracavitary flow direction observed during each phase of the cardiac cycle. Integrating the LV structure with electrical activation and motion sequences observed in vivo provides an understanding about the spatiotemporal sequence of regional myocardial performance that is essential for noninvasive cardiac imaging.
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Affiliation(s)
- Partho P Sengupta
- Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA
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44
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Stehle R, Solzin J, Iorga B, Gomez D, Blaudeck N, Pfitzer G. Mechanical properties of sarcomeres during cardiac myofibrillar relaxation: stretch-induced cross-bridge detachment contributes to early diastolic filling. J Muscle Res Cell Motil 2006; 27:423-34. [PMID: 16897577 DOI: 10.1007/s10974-006-9072-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Accepted: 06/16/2006] [Indexed: 12/01/2022]
Abstract
Sudden Ca2+ removal from isometrically contracting cardiac myofibrils induces a biphasic relaxation: first a slow, linear force decline during which sarcomeres remain isometric and then a rapid, exponential decay originating from sequential lengthening, i.e., successive mechanical relaxation, of individual sarcomeres (Stehle et al. 2002; Biophys J 83:2152-2162). Step-stretches were applied to the myofibrils, in order to study the mechanical properties of sarcomeres during this dynamic relaxation process. Stretch applied soon (approximately 10 ms) after Ca2+ removal accelerated the initiation of the rapid, exponential force decay and of the sequential sarcomere lengthening. After the stretch, a short, transient period (approximately 24 ms) remained, during which time force was enhanced and sarcomeres were homogenously elongated by the stretch. This period was similar to the duration of the switching-off of troponin C in myofibrils, as measured by stopped-flow. In contrast, when the stretch was applied during the rapid, exponential relaxation phase, force quickly decayed after stretch, back to the force level of isometric controls or even lower. Smaller stretches lengthened only those sarcomeres that were located at the wave front of the sequential sarcomere relaxation. The more the stretch-size was increased, the more of the contracting sarcomeres became lengthened by the stretch; those sarcomeres that were relaxed prior to stretch were barely elongated. These results indicate that the stretch accelerates myofibrillar relaxation by forcing the cross-bridges in contracting sarcomeres to detach. Subsequent rapid cross-bridge reattachment occurs during a short period after Ca2+ removal until troponin C is switched off. However, this switch off occurs approximately 5 times too fast to directly rate-limit the force relaxation under the isometric condition. After troponin C is switched off, stretching induces cross-bridge detachment without subsequent reattachment, and force rapidly decays below the isometric level. This may explain the rapid distention of the ventricular myocardium during early diastolic filling.
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Affiliation(s)
- R Stehle
- Institute of Vegetative Physiology, and Center of Molecular Medicine Cologne, University of Cologne, Robert-Koch-Str. 39, D-50931, Köln, Germany.
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Kelly D, Mackenzie L, Hunter P, Smaill B, Saint DA. GENE EXPRESSION OF STRETCH-ACTIVATED CHANNELS AND MECHANOELECTRIC FEEDBACK IN THE HEART. Clin Exp Pharmacol Physiol 2006; 33:642-8. [PMID: 16789934 DOI: 10.1111/j.1440-1681.2006.04392.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. Mechanoelectric feedback (MEF) in the heart is the process by which mechanical forces on the myocardium can change its electrical properties. Mechanoelectric feedback has been demonstrated in many animal models, ranging from isolated cells, through isolated hearts to whole animals. In humans, MEF has been demonstrated directly in both the atria and the ventricles. It seems likely that MEF provides either the trigger or the substrate for some types of clinically important arrhythmias. 2. Mechanoelectric feedback may arise because of the presence of stretch-sensitive (or mechano-sensitive) ion channels in the cell membrane of the cardiac myocytes. Two types have been demonstrated: (i) a non-specific cation channel (stretch-activated channel (SAC); conductance of approximately 25 pS); and (ii) a potassium channel with a conductance of approximately 100 pS. The gene coding for the SAC has not yet been identified. The gene for the potassium channel is likely to be TREK, a member of the tandem pore potassium channel gene family. We have recorded stretch-sensitive potassium channels in rat isolated myocytes that have the properties of TREK channels expressed in heterologous systems. 3. It has been shown that TREK mRNA is expressed heterogeneously in the rat ventricular wall, with 17-fold more expression in endocardial compared with epicardial cells. This difference is reflected in the TREK currents recorded from endocardial and epicardial cells using whole-cell patch-clamp techniques, although the difference in current density was less pronounced (approximately threefold). Consistent with this, we show here that when the ventricle is stretched by inflation of an intraventricular balloon in a Langendorff perfused rat isolated heart, action potential shortening was more pronounced in the endocardium (30% shortening at 40 mmHg) compared with that in the epicardium (10% shortening at the same pressure). 4. Computer models of the mechanics of the (pig) heart show pronounced spatial variations in strain in the myocardium with large transmural differences (in the left ventricle in particular) and also large differences between the base and apex of the ventricle. 5. The importance of MEF and the non-homogeneous gene expression and strain distribution for arrhythmias is discussed.
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Affiliation(s)
- D Kelly
- School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
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46
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Helm PA, Tseng HJ, Younes L, McVeigh ER, Winslow RL. Ex vivo 3D diffusion tensor imaging and quantification of cardiac laminar structure. Magn Reson Med 2006; 54:850-9. [PMID: 16149057 PMCID: PMC2396270 DOI: 10.1002/mrm.20622] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A three-dimensional (3D) diffusion-weighted imaging (DWI) method for measuring cardiac fiber structure at high spatial resolution is presented. The method was applied to the ex vivo reconstruction of the fiber architecture of seven canine hearts. A novel hypothesis-testing method was developed and used to show that distinct populations of secondary and tertiary eigenvalues may be distinguished at reasonable confidence levels (P < or = 0.01) within the canine ventricle. Fiber inclination and sheet angles are reported as a function of transmural depth through the anterior, lateral, and posterior left ventricle (LV) free wall. Within anisotropic regions, two consistent and dominant orientations were identified, supporting published results from histological studies and providing strong evidence that the tertiary eigenvector of the diffusion tensor (DT) defines the sheet normal.
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Affiliation(s)
- Patrick A Helm
- Center for Cardiovascular Bioinformatics and Modeling, Johns Hopkins University, Baltimore, MD 21218, USA.
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47
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Chen J, Liu W, Zhang H, Lacy L, Yang X, Song SK, Wickline SA, Yu X. Regional ventricular wall thickening reflects changes in cardiac fiber and sheet structure during contraction: quantification with diffusion tensor MRI. Am J Physiol Heart Circ Physiol 2005; 289:H1898-907. [PMID: 16219812 DOI: 10.1152/ajpheart.00041.2005] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Dynamic changes of myocardial fiber and sheet structure are key determinants of regional ventricular function. However, quantitative characterization of the contraction-related changes in fiber and sheet structure has not been reported. The objective of this study was to quantify cardiac fiber and sheet structure at selected phases of the cardiac cycle. Diffusion tensor MRI was performed on isolated, perfused Sprague-Dawley rat hearts arrested or fixed in three states as follows: 1) potassium arrested (PA), which represents end diastole; 2) barium-induced contracture with volume (BV+), which represents isovolumic contraction or early systole; and 3) barium-induced contracture without volume (BV-), which represents end systole. Myocardial fiber orientations at the base, midventricle, and apex were determined from the primary eigenvectors of the diffusion tensor. Sheet structure was determined from the secondary and tertiary eigenvectors at the same locations. We observed that the transmural distribution of the myofiber helix angle remained unchanged as contraction proceeded from PA to BV+, but endocardial and epicardial fibers became more longitudinally orientated in the BV- group. Although sheet structure exhibited significant regional variations, changes in sheet structure during myocardial contraction were relatively uniform across regions. The magnitude of the sheet angle, which is an index of local sheet slope, decreased by 23 and 44% in BV+ and BV- groups, respectively, which suggests more radial orientation of the sheet. In summary, we have shown for the first time that geometric changes in both sheet and fiber orientation provide a substantial mechanism for radial wall thickening independent of active components due to myofiber shortening. Our results provide direct evidence that sheet reorientation is a primary determinant of myocardial wall thickening.
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Affiliation(s)
- Junjie Chen
- Cardiovascular Magnetic Resonance Laboratories, Department of Medicine, Washington University, St Louis, Missouri, USA
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48
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Veress AI, Gullberg GT, Weiss JA. Measurement of Strain in the Left Ventricle during Diastole with cine-MRI and Deformable Image Registration. J Biomech Eng 2005; 127:1195-207. [PMID: 16502662 DOI: 10.1115/1.2073677] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The assessment of regional heart wall motion (local strain) can localize ischemic myocardial disease, evaluate myocardial viability, and identify impaired cardiac function due to hypertrophic or dilated cardiomyopathies. The objectives of this research were to develop and validate a technique known as hyperelastic warping for the measurement of local strains in the left ventricle from clinical cine-magnetic resonance imaging (MRI) image datasets. The technique uses differences in image intensities between template (reference) and target (loaded) image datasets to generate a body force that deforms a finite element (FE) representation of the template so that it registers with the target image. To validate the technique, MRI image datasets representing two deformation states of a left ventricle were created such that the deformation map between the states represented in the images was known. A beginning diastolic cine-MRI image dataset from a normal human subject was defined as the template. A second image dataset (target) was created by mapping the template image using the deformation results obtained from a forward FE model of diastolic filling. Fiber stretch and strain predictions from hyperelastic warping showed good agreement with those of the forward solution (R2=0.67 stretch, R2=0.76 circumferential strain, R2=0.75 radial strain, and R2=0.70 in-plane shear). The technique had low sensitivity to changes in material parameters (deltaR2= -0.023 fiber stretch, deltaR2=-0.020 circumferential strain, deltaR2=-0.005 radial strain, and deltaR2=0.0125 shear strain with little or no change in rms error), with the exception of changes in bulk modulus of the material. The use of an isotropic hyperelastic constitutive model in the warping analyses degraded the predictions of fiber stretch. Results were unaffected by simulated noise down to a signal-to-noise ratio (SNR) of 4.0 (deltaR2= -0.032 fiber stretch, deltaR2=-0.023 circumferential strain, deltaR2=-0.04 radial strain, and deltaAR2=0.0211 shear strain with little or no increase in rms error). This study demonstrates that warping in conjunction with cine-MRI imaging can be used to determine local ventricular strains during diastole.
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Affiliation(s)
- Alexander I Veress
- Department of Bioengineering, and Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT 84112-9202, USA
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49
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McCulloch AD. Functionally and structurally integrated computational modeling of ventricular physiology. ACTA ACUST UNITED AC 2005; 54:531-9. [PMID: 15760485 DOI: 10.2170/jjphysiol.54.531] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Computational biology is integrative in several ways. Functionally, computational models are valuable for integrating the many interacting processes within biochemical networks and the many interacting physiological subsystems within the cell. Structurally detailed models provide a way of integrating across scales of biological organization from molecule to organism. Data integration across diverse laboratory and clinical measurements is another unique strength of computational biology. We describe examples of all three categories of integration by using recent advances in modeling cardiac excitation-contraction coupling and whole-heart electromechanics in health and disease.
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Affiliation(s)
- Andrew D McCulloch
- Department of Bioengineering, Whitaker Institute for Biomedical Engineering, University of California San Diego, La Jolla, CA 92093-0412, USA.
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50
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Cheng A, Langer F, Rodriguez F, Criscione JC, Daughters GT, Miller DC, Ingels NB. Transmural cardiac strains in the lateral wall of the ovine left ventricle. Am J Physiol Heart Circ Physiol 2005; 288:H1546-56. [PMID: 15591101 DOI: 10.1152/ajpheart.00716.2004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The constant-volume property of contracting cardiac muscle has been invoked in models of heart wall mechanics that predict that systolic subendocardial left ventricular (LV) wall thickening must significantly exceed subepicardial thickening. To examine this prediction, we implanted arrays of radiopaque markers to measure lateral equatorial wall transmural strains and global and regional LV geometry in seven sheep and studied the four-dimensional dynamics of these arrays using biplane videofluoroscopy (60 Hz) in anesthetized intact animals 1 and 8 wk after surgery. A transmural gradient of systolic lateral wall thickening was observed at 1 wk ( P = 0.009; linear regression) but was no longer present at 8 wk ( P = 0.243). Referenced to end diastole, group mean (±SD) end-systolic radial subepicardial, midwall, and subendocardial wall thickening strains were, respectively, 0.08 ± 0.08, 0.14 ± 0.08, and 0.22 ± 0.12 at 1 wk and 0.19 ± 0.07 ( P = 0.02; 1 vs. 8 wk), 0.20 ± 0.04, and 0.23 ± 0.07 at 8 wk. With the exception of an 8-ml (7%) increase in end-diastolic volume ( P = 0.04) from 1 to 8 wk, LV shape and hemodynamics were otherwise unchanged. We conclude that equivalent hemodynamics can be generated by the left ventricle with or without a transmural gradient of systolic wall thickening in this region; thus such a gradient is unlikely to be a fundamental property of the contracting LV myocardium. We discuss some implications of these findings regarding mechanisms involved in systolic wall thickening.
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Affiliation(s)
- Allen Cheng
- Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine, Stanford, CA, USA
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