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Electromechanical effects of concentric hypertrophy on the left ventricle: A simulation study. Comput Biol Med 2018; 99:236-256. [DOI: 10.1016/j.compbiomed.2018.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Revised: 06/06/2018] [Accepted: 06/07/2018] [Indexed: 11/19/2022]
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Orini M, Taggart P, Lambiase PD. In vivo human sock-mapping validation of a simple model that explains unipolar electrogram morphology in relation to conduction-repolarization dynamics. J Cardiovasc Electrophysiol 2018; 29:990-997. [PMID: 29660191 PMCID: PMC6055721 DOI: 10.1111/jce.13606] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2018] [Revised: 03/29/2018] [Accepted: 04/09/2018] [Indexed: 12/16/2022]
Abstract
INTRODUCTION The unipolar electrogram (UEG) provides local measures of cardiac activation and repolarization and is an important translational link between patient and laboratory. A simple theoretical model of the UEG was previously proposed and tested in silico. METHOD AND RESULTS The aim of this study was to use epicardial sock-mapping data to validate the simple model's predictions of unipolar electrogram morphology in the in vivo human heart. The simple model conceptualizes the UEG as the difference between a local cardiac action potential and a position-independent component representing remote activity, which is defined as the average of all action potentials. UEGs were recorded in 18 patients using a multielectrode sock containing 240 electrodes and activation (AT) and repolarization time (RT) were measured using standard definitions. For each cardiac site, a simulated local action potential was generated by adjusting a stylized action potential to fit AT and RT measured in vivo. The correlation coefficient (cc) measuring the morphological similarity between 13,637 recorded and simulated UEGs was cc = 0.89 (0.72-0.95), median (Q1 -Q3 ), for the entire UEG, cc = 0.90 (0.76-0.95) for QRS complexes, and cc = 0.83 (0.58-0.92) for T-waves. QRS and T-wave areas from recorded and simulated UEGs showed cc> 0.89 and cc> 0.84, respectively, indicating good agreement between voltage isochrones maps. Simulated UEGs accurately reproduced the interaction between AT and QRS morphology and between RT and T-wave morphology observed in vivo. CONCLUSIONS Human in vivo whole heart data support the validity of the simple model, which provides a framework for improving the understanding of the UEG and its clinical utility.
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Affiliation(s)
- Michele Orini
- Department of Mechanical Engineering, University College London, London, United Kingdom.,Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom
| | - Peter Taggart
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom.,Institute of Cardiovascular Science, University College London, London, United Kingdom
| | - Pier D Lambiase
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom.,Institute of Cardiovascular Science, University College London, London, United Kingdom
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Orini M, Taggart P, Srinivasan N, Hayward M, Lambiase PD. Interactions between Activation and Repolarization Restitution Properties in the Intact Human Heart: In-Vivo Whole-Heart Data and Mathematical Description. PLoS One 2016; 11:e0161765. [PMID: 27588688 PMCID: PMC5010207 DOI: 10.1371/journal.pone.0161765] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 08/11/2016] [Indexed: 01/28/2023] Open
Abstract
BACKGROUND The restitution of the action potential duration (APDR) and conduction velocity (CVR) are mechanisms whereby cardiac excitation and repolarization adapt to changes in heart rate. They modulate the vulnerability to dangerous arrhythmia, but the mechanistic link between restitution and arrhythmogenesis remains only partially understood. METHODS This paper provides an experimental and theoretical study of repolarization and excitation restitution properties and their interactions in the intact human epicardium. The interdependence between excitation and repolarization dynamic is studied in 8 patients (14 restitution protocols, 1722 restitution curves) undergoing global epicardial mapping with multi-electrode socks before open heart surgery. A mathematical description of the contribution of both repolarization and conduction dynamics to the steepness of the APDR slope is proposed. RESULTS This study demonstrates that the APDR slope is a function of both activation and repolarization dynamics. At short cycle length, conduction delay significantly increases the APDR slope by interacting with the diastolic interval. As predicted by the proposed mathematical formulation, the APDR slope was more sensitive to activation time prolongation than to the simultaneous shortening of repolarization time. A steep APDR slope was frequently identified, with 61% of all cardiac sites exhibiting an APDR slope > 1, suggesting that a slope > 1 may not necessarily promote electrical instability in the human epicardium. APDR slope did not change for different activation or repolarization times, and it was not a function of local baseline APD. However, it was affected by the spatial organization of electrical excitation, suggesting that in tissue APDR is not a unique function of local electrophysiological properties. Spatial heterogeneity in both activation and repolarization restitution contributed to the increase in the modulated dispersion of repolarization, which for short cycle length was as high as 250 ms. Heterogeneity in conduction velocity restitution can translate into both activation and repolarization dispersion and increase cardiac instability. The proposed mathematical formulation shows an excellent agreement with the experimental data (correlation coefficient r = 0.94) and provides a useful tool for the understanding of the complex interactions between activation and repolarization restitution properties as well as between their measurements.
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Affiliation(s)
- Michele Orini
- Institute of Cardiovascular Science, University College London, London, United Kingdom
- Barts Heart Centre, St Bartholomews Hospital, London, United Kingdom
| | - Peter Taggart
- Institute of Cardiovascular Science, University College London, London, United Kingdom
| | - Neil Srinivasan
- Institute of Cardiovascular Science, University College London, London, United Kingdom
- Barts Heart Centre, St Bartholomews Hospital, London, United Kingdom
| | - Martin Hayward
- The Heart Hospital, University College London Hospitals, London, United Kingdom
| | - Pier D. Lambiase
- Institute of Cardiovascular Science, University College London, London, United Kingdom
- Barts Heart Centre, St Bartholomews Hospital, London, United Kingdom
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Srinivasan NT, Orini M, Simon RB, Providência R, Khan FZ, Segal OR, Babu GG, Bradley R, Rowland E, Ahsan S, Chow AW, Lowe MD, Taggart P, Lambiase PD. Ventricular stimulus site influences dynamic dispersion of repolarization in the intact human heart. Am J Physiol Heart Circ Physiol 2016; 311:H545-54. [PMID: 27371682 PMCID: PMC5142177 DOI: 10.1152/ajpheart.00159.2016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 06/29/2016] [Indexed: 12/18/2022]
Abstract
Spatial variation of restitution in relation to varying stimulus site is poorly defined in the intact human heart. Repolarization gradients were shown to be dependent on site of activation with epicardial stimulation promoting significant transmural gradients. Steep restitution slopes were predominant in the normal ventricle. The spatial variation in restitution properties in relation to varying stimulus site is poorly defined. This study aimed to investigate the effect of varying stimulus site on apicobasal and transmural activation time (AT), action potential duration (APD) and repolarization time (RT) during restitution studies in the intact human heart. Ten patients with structurally normal hearts, undergoing clinical electrophysiology studies, were enrolled. Decapolar catheters were placed apex to base in the endocardial right ventricle (RVendo) and left ventricle (LVendo), and an LV branch of the coronary sinus (LVepi) for transmural recording. S1–S2 restitution protocols were performed pacing RVendo apex, LVendo base, and LVepi base. Overall, 725 restitution curves were analyzed, 74% of slopes had a maximum slope of activation recovery interval (ARI) restitution (Smax) > 1 (P < 0.001); mean Smax = 1.76. APD was shorter in the LVepi compared with LVendo, regardless of pacing site (30-ms difference during RVendo pacing, 25-ms during LVendo, and 48-ms during LVepi; 50th quantile, P < 0.01). Basal LVepi pacing resulted in a significant transmural gradient of RT (77 ms, 50th quantile: P < 0.01), due to loss of negative transmural AT-APD coupling (mean slope 0.63 ± 0.3). No significant transmural gradient in RT was demonstrated during endocardial RV or LV pacing, with preserved negative transmural AT-APD coupling (mean slope −1.36 ± 1.9 and −0.71 ± 0.4, respectively). Steep ARI restitution slopes predominate in the normal ventricle and dynamic ARI; RT gradients exist that are modulated by the site of activation. Epicardial stimulation to initiate ventricular activation promotes significant transmural gradients of repolarization that could be proarrhythmic.
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Affiliation(s)
- Neil T Srinivasan
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and Institute of Cardiovascular Science, University College London, London, United Kingdom
| | - Michele Orini
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and Institute of Cardiovascular Science, University College London, London, United Kingdom
| | - Ron B Simon
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Rui Providência
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Fakhar Z Khan
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Oliver R Segal
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Girish G Babu
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Richard Bradley
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Edward Rowland
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Syed Ahsan
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Anthony W Chow
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Martin D Lowe
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and
| | - Peter Taggart
- Institute of Cardiovascular Science, University College London, London, United Kingdom
| | - Pier D Lambiase
- Department of Cardiac Electrophysiology, The Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom; and Institute of Cardiovascular Science, University College London, London, United Kingdom
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Perotti LE, Krishnamoorthi S, Borgstrom NP, Ennis DB, Klug WS. Regional segmentation of ventricular models to achieve repolarization dispersion in cardiac electrophysiology modeling. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2015; 31:10.1002/cnm.2718. [PMID: 25845576 PMCID: PMC4519348 DOI: 10.1002/cnm.2718] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Revised: 03/01/2015] [Accepted: 03/31/2015] [Indexed: 05/08/2023]
Abstract
The electrocardiogram (ECG) is one of the most significant outputs of a computational model of cardiac electrophysiology because it relates the numerical results to clinical data and is a universal tool for diagnosing heart diseases. One key features of the ECG is the T-wave, which is caused by longitudinal and transmural heterogeneity of the action potential duration (APD). Thus, in order to model a correct wave of repolarization, different cell properties resulting in different APDs must be assigned across the ventricular wall and longitudinally from apex to base. To achieve this requirement, a regional parametrization of the heart is necessary. We propose a robust approach to obtain the transmural and longitudinal segmentation in a general heart geometry without relying on ad hoc procedures. Our approach is based on auxiliary harmonic lifting analyses, already used in the literature to generate myocardial fiber orientations. Specifically, the solution of a sequence of Laplace boundary value problems allows parametrically controlled segmentation of both heart ventricles. The flexibility and simplicity of the proposed method is demonstrated through several representative examples, varying the locations and extents of the epicardial, midwall, and endocardial layers. Effects of the control parameters on the T-wave morphology are illustrated via computed ECGs.
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Affiliation(s)
- L. E. Perotti
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California, United States of America
- Department of Bioengineering, University of California, Los Angeles, California, United States of America
- Department of Radiological Sciences, University of California, Los Angeles, California, United States of America
| | - S. Krishnamoorthi
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California, United States of America
| | - N. P. Borgstrom
- Department of Bioengineering, University of California, Los Angeles, California, United States of America
| | - D. B. Ennis
- Department of Bioengineering, University of California, Los Angeles, California, United States of America
- Department of Radiological Sciences, University of California, Los Angeles, California, United States of America
| | - W. S. Klug
- Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California, United States of America
- Correspondence to: Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, United States of America.
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Western D, Hanson B, Taggart P. Measurement bias in activation-recovery intervals from unipolar electrograms. Am J Physiol Heart Circ Physiol 2014; 308:H331-8. [PMID: 25398981 PMCID: PMC4315451 DOI: 10.1152/ajpheart.00478.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The activation-recovery interval (ARI) calculated from unipolar electrograms is regularly used as a convenient surrogate measure of local cardiac action potential durations (APD). This method enables important research bridging between computational studies and in vitro and in vivo human studies. The Wyatt method is well established as a theoretically sound method for calculating ARIs; however, some studies have observed that it is prone to a bias error in measurement when applied to positive T waves. This article demonstrates that recent theoretical and computational studies supporting the use of the Wyatt method are likely to have underestimated the extent of this bias in many practical experimental recording scenarios. This work addresses these situations and explains the measurement bias by adapting existing theoretical expressions of the electrogram to represent practical experimental recording configurations. A new analytic expression for the electrogram's local component is derived, which identifies the source of measurement bias for positive T waves. A computer implementation of the new analytic model confirms our hypothesis that the bias is systematically dependent on the electrode configuration. These results provide an aid to electrogram interpretation in general, and this work's outcomes are used to make recommendations on how to minimize measurement error.
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Affiliation(s)
- David Western
- Department of Mechanical Engineering, University College London, London, United Kingdom; Department of Mechanical Engineering, University of Bristol, Bristol, United Kingdom; and
| | - Ben Hanson
- Department of Mechanical Engineering, University College London, London, United Kingdom
| | - Peter Taggart
- Neurocardiology Unit, University College London Hospitals, London, United Kingdom
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Dal H, Göktepe S, Kaliske M, Kuhl E. A fully implicit finite element method for bidomain models of cardiac electromechanics. COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2013; 253:323-336. [PMID: 23175588 PMCID: PMC3501134 DOI: 10.1016/j.cma.2012.07.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
We propose a novel, monolithic, and unconditionally stable finite element algorithm for the bidomain-based approach to cardiac electromechanics. We introduce the transmembrane potential, the extracellular potential, and the displacement field as independent variables, and extend the common two-field bidomain formulation of electrophysiology to a three-field formulation of electromechanics. The intrinsic coupling arises from both excitation-induced contraction of cardiac cells and the deformation-induced generation of intra-cellular currents. The coupled reaction-diffusion equations of the electrical problem and the momentum balance of the mechanical problem are recast into their weak forms through a conventional isoparametric Galerkin approach. As a novel aspect, we propose a monolithic approach to solve the governing equations of excitation-contraction coupling in a fully coupled, implicit sense. We demonstrate the consistent linearization of the resulting set of non-linear residual equations. To assess the algorithmic performance, we illustrate characteristic features by means of representative three-dimensional initial-boundary value problems. The proposed algorithm may open new avenues to patient specific therapy design by circumventing stability and convergence issues inherent to conventional staggered solution schemes.
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Affiliation(s)
- Hüsnü Dal
- Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland
- Institute for Structural Analysis, Technische Universität Dresden, Dresden, Germany
- Institut für Mechanik, (Bauwesen), Lehrstuhl I, Universität Stuttgart, Germany
| | - Serdar Göktepe
- Department of Civil Engineering, Middle East Technical University, Ankara, Turkey
| | - Michael Kaliske
- Institute for Structural Analysis, Technische Universität Dresden, Dresden, Germany
| | - Ellen Kuhl
- Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland
- Department of Mechanical Engineering, Stanford University, Stanford, USA
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Potse M. Mathematical modeling and simulation of ventricular activation sequences: implications for cardiac resynchronization therapy. J Cardiovasc Transl Res 2012; 5:146-58. [PMID: 22282106 PMCID: PMC3294217 DOI: 10.1007/s12265-011-9343-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Accepted: 12/18/2011] [Indexed: 02/04/2023]
Abstract
Next to clinical and experimental research, mathematical modeling plays a crucial role in medicine. Biomedical research takes place on many different levels, from molecules to the whole organism. Due to the complexity of biological systems, the interactions between components are often difficult or impossible to understand without the help of mathematical models. Mathematical models of cardiac electrophysiology have made a tremendous progress since the first numerical ECG simulations in the 1960s. This paper briefly reviews the development of this field and discusses some example cases where models have helped us forward, emphasizing applications that are relevant for the study of heart failure and cardiac resynchronization therapy.
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Affiliation(s)
- Mark Potse
- Institute of Computational Science, University of Lugano, Via Giuseppe Buffi 13, 6904 Lugano, Switzerland.
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Sassi R, Mainardi LT. An Estimate of the Dispersion of Repolarization Times Based on a Biophysical Model of the ECG. IEEE Trans Biomed Eng 2011; 58:3396-405. [DOI: 10.1109/tbme.2011.2166263] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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