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Alimorad G, Taing M, Frisbee JC, Goldman D, Kharche SR. Quantifying Longitudinal Network Geometry Alterations in Rat Skeletal Microvasculature Subject to Ischemia. FASEB J 2022. [DOI: 10.1096/fasebj.2022.36.s1.r2638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Melvin Taing
- Computer ScienceThe University of Western OntarioLondonON
| | | | - Daniel Goldman
- Medical BiophysicsThe University of Western OntarioLondonON
| | - Sanjay R. Kharche
- Medical BiophysicsThe University of Western OntarioLondonON
- Kidney Clinical Research UnitLawson Health Research InstituteLondonON
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Kharche SR, Dobrzynski H, Goldman D. Editorial: Vascular Disease Multi-Scale Multi-Physics Modeling and Experimental Data. Front Physiol 2022; 13:865905. [PMID: 35370803 PMCID: PMC8970683 DOI: 10.3389/fphys.2022.865905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Accepted: 02/21/2022] [Indexed: 11/24/2022] Open
Affiliation(s)
- Sanjay R. Kharche
- Department of Medical Biophysics, Western University, London, ON, Canada
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
- Kidney Clinical Research Unit, Lawson Health Research Institute, London, ON, Canada
- *Correspondence: Sanjay R. Kharche
| | - Halina Dobrzynski
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
- Department of Anatomy, Jagiellonian University Medical College, Kraków, Poland
| | - Daniel Goldman
- Department of Medical Biophysics, Western University, London, ON, Canada
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Kharche SR, Lemoine S, Tamasi T, Hur L, So A, McIntyre CW. Therapeutic Hypothermia Reduces Peritoneal Dialysis Induced Myocardial Blood Flow Heterogeneity and Arrhythmia. Front Med (Lausanne) 2021; 8:700824. [PMID: 34395480 PMCID: PMC8362929 DOI: 10.3389/fmed.2021.700824] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 06/30/2021] [Indexed: 11/13/2022] Open
Abstract
Background: Moderate therapeutic hypothermia (TH) is a well-recognized cardio-protective strategy. The instillation of fluid into the peritoneum provides an opportunity to deliver moderate hypothermia as primary prevention against cardiovascular events. We aimed to to investigate both cardiac perfusion consequences (overall blood flow and detailed assessment of perfusion heterogeneity) and subsequently simulate the associated arrhythmic risk for patients undergoing peritoneal dialysis (PD) induced TH. Methods: Patients underwent high resolution myocardial perfusion scanning using high resolution 256 slice CT scanning, at rest and with adenosine stress. The first visit using the patient's usual PD regimen, on the second visit the same regime was utilized but with cooled peritoneal dialysate at 32°C. Myocardial blood flow (MBF) was quantified from generated perfusion maps, reconstructed in 3D. MBF heterogeneity was assessed by fractal dimension (FD) measurement on the 3D left ventricular reconstruction. Arrhythmogenicity was quantified from a sophisticated computational simulation using a multi-scale human 3D ventricle wedge electrophysiological computational model. Results: We studied 7 PD patients, mean age of 60 ± 7 and mean vintage dialysis of 23.6 ± 17.6 months. There were no significant different in overall segmental MBF between normothermic condition (NT) and TH. MBF heterogeneity was significantly decreased (-14%, p = 0.03) at rest and after stress (-14%, p = 0.03) when cooling was applied. Computational simulation showed that TH allowed a normalization of action potential, QT duration and T wave. Conclusion: TH-PD results in moderate hypothermia leading to a reduction in perfusion heterogeneity and simulated risk of non-terminating malignant ventricular arrhythmias.
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Affiliation(s)
- Sanjay R Kharche
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada.,Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
| | - Sandrine Lemoine
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada
| | - Tanya Tamasi
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada
| | - Lisa Hur
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada
| | - Aaron So
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada.,Imaging Program, Lawson Health Research Institute, London, ON, Canada
| | - Christopher W McIntyre
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada.,Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
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Joseph JJ, McIntyre CW, Kharche SR. Proarrhythmic Effects of Electrolyte Imbalance in Virtual Human Atrial and Ventricular Cardiomyocytes. Annu Int Conf IEEE Eng Med Biol Soc 2020; 2020:2315-2318. [PMID: 33018471 DOI: 10.1109/embc44109.2020.9176060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dialysis is prescribed to renal failure patients as a long-term chronic treatment. Whereas dialysis therapeutically normalizes serum electrolytes and removes small toxin molecules, it fails to alleviate fibroblast induced structural fibrosis, and unresponsive uremia. The simultaneous presence of altered electrolytes and fibrosis or uremia is thought to be pro-arrhythmogenic. This study explored potential arrhythmogenesis under pre-dialysis (high electrolyte levels) and post-dialysis (low physiological electrolyte levels) in the presence of fibrosis and uremia in human atrial and ventricular model cardiomyocytes.Two validated human cardiomyocyte models were used in this study that permitted simulation of cardiac atrial and ventricular detailed electrophysiology. Pathological conditions simulating active fibrosis and uremia were implemented in both models. Pre- and post-dialysis conditions were simulated using high and low electrolyte levels respectively. Arrythmogenesis was quantified by computing restitution curves that permitted identification of action potential duration and calcium transient alternans instabilities.In comparison to control conditions, fibrosis abbreviated action potential durations while uremia prolonged the same. Under pre-dialysis conditions, an elevation of serum electrolyte levels caused action potential durations to be abbreviated under both fibrosis and uremia. Alternans instability was observed in the ventricular cardiomyocyte model. Under post-dialysis conditions, lower levels of serum electrolytes promoted an abbreviated action potential duration under fibrosis but caused a large increase of the control and uremic action potential durations. Alternans instabilities were observed in the atrial cardiomyocyte model under post-dialysis conditions at physiological heart rates. The calcium transient restitution showed similar alternans instabilities.Co-existing conditions such as fibrosis and uremia in the presence of unphysiological electrolyte levels promote arrhythmogenesis and may require additional treatment to improve dialysis outcomes.Clinical Relevance. Knowledge of model response to clinically relevant conditions permits use of in silico modeling to better understand and dissect underlying arrhythmia mechanisms.
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Kharche SR, Desai K, McIntyre CW. Elucidating the relationship between arrhythmia and ischemic heterogeneity: an in silico study. Annu Int Conf IEEE Eng Med Biol Soc 2020; 2020:2434-2437. [PMID: 33018498 DOI: 10.1109/embc44109.2020.9176737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Dialysis causes blood flow defects in the heart that may augment electrophysiological heterogeneity in the form of increased number of ischemic zones in the human left ventricle. We computationally tested whether a larger number of ischemic zones aggravate arrhythmia using a 2D electrophysiological model of the human ventricle.A human ventricle cardiomyocyte model capable of simulating ischemic action potentials was adapted in this study. The cell model was incorporated into a spatial 2D model consisting of known number of ischemic zones. Inter-cellular gap junction coupling within ischemic zones was reduced to simulate slow conduction. Arrhythmia severity was assessed by inducing a re-entry, and quantifying the ensuing breakup and tissue pacing rates.Ischemia elevated the isolated cardiomyocyte's resting potential and reduced its action potential duration. In the absence of ischemic zones, the propensity in the 2D model to induce multiple re-entrant waves was low. The inclusion of ischemic zones provided the substrate for initiation of re-entrant waves leading to fibrillation. Dominant frequency, which measured the highest rate of pacing in the tissue, increased drastically with the inclusion of multiple ischemic zones. Re-entrant wave tip maximum numbers increased from 1 tip (no ischemic zone) to 34 tips when a large number (20) of ischemic zones were included. Computational limiting factors of our platform were identified using software profiling.Clinical significance. Dialysis may promote deleterious arrhythmias by increasing tissue level action potential dispersion.
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Altamirano-Diaz L, Kassay AD, Serajelahi B, McIntyre CW, Filler G, Kharche SR. Arterial Hypertension and Unusual Ascending Aortic Dilatation in a Neonate With Acute Kidney Injury: Mechanistic Computer Modeling. Front Physiol 2019; 10:1391. [PMID: 31780955 PMCID: PMC6856675 DOI: 10.3389/fphys.2019.01391] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 10/25/2019] [Indexed: 01/23/2023] Open
Abstract
Background Neonatal asphyxia caused kidney injury and severe hypertension in a newborn. An unusually dilatated ascending aorta developed. Dialysis and pharmacological treatment led to partial recovery of the ascending aortic diameters. It was hypothesized that the aortic dilatation may be associated with aortic stiffening, peripheral resistance, and cardiovascular changes. Mathematical modeling was used to better understand the potential causes of the hypertension, and to confirm our clinical treatment within the confines of the model's capabilities. Methods The patient's systolic arterial blood pressure showed hypertension. Echocardiographic exams showed ascending aorta dilatation during hypertension, which partially normalized upon antihypertensive treatment. To explore the underlying mechanisms of the aortic dilatation and hypertension, an existing lumped parameter hemodynamics model was deployed. Hypertension was simulated using realistic literature informed parameter values. It was also simulated using large parameter perturbations to demonstrate effects. Simulations were designed to permit examination of causal mechanisms. The hypertension inducing effects of aortic stiffnesses, vascular resistances, and cardiac hypertrophy on blood flow and pressure were simulated. Sensitivity analysis was used to stratify causes. Results In agreement with our clinical diagnosis, the model showed that an increase of aortic stiffness followed by augmentation of peripheral resistance are the prime causes of realistic hypertension. Increased left ventricular elastance may also cause hypertension. Ascending aortic pressure and flow increased in the simultaneous presence of left ventricle hypertrophy and augmented small vessel resistance, which indicate a plausible condition for ascending aorta dilatation. In case of realistic hypertension, sensitivity analysis showed that the treatment of both the large vessel stiffness and small vessel resistance are more important in comparison to cardiac hypertrophy. Conclusion and Discussion Large vessel stiffness was found to be the prime factor in arterial hypertension, which confirmed the clinical treatment. Treatment of cardiac hypertrophy appears to provide significant benefit but may be secondary to treatment of large vessel stiffness. The quantitative grading of pathophysiological mechanisms provided by the modeling may contribute to treatment recommendations. The model was limited due to a lack of data suitable to permit model identification.
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Affiliation(s)
- Luis Altamirano-Diaz
- Department of Paediatrics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.,Children's Health Research Institute, London, ON, Canada.,Paediatric Cardiopulmonary Research Laboratory, LHSC, London, ON, Canada
| | | | - Baran Serajelahi
- Department of Medicine, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
| | - Christopher W McIntyre
- Department of Paediatrics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.,Lawson Health Research Institute, London, ON, Canada.,Department of Medical Biophysics, Western University, London, ON, Canada
| | - Guido Filler
- Department of Paediatrics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.,Children's Health Research Institute, London, ON, Canada.,Lawson Health Research Institute, London, ON, Canada.,Department of Medical Biophysics, Western University, London, ON, Canada
| | - Sanjay R Kharche
- Lawson Health Research Institute, London, ON, Canada.,Department of Medicine, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.,Department of Medical Biophysics, Western University, London, ON, Canada
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Sheard TMD, Kharche SR, Pinali C, Shiels HA. 3D ultrastructural organisation of calcium release units in the avian sarcoplasmic reticulum. J Exp Biol 2019; 222:jeb.197640. [DOI: 10.1242/jeb.197640] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 02/22/2019] [Indexed: 11/20/2022]
Abstract
Excitation-contraction coupling in vertebrate hearts is underpinned by calcium (Ca2+) release from Ca2+ release units (CRUs). CRUs are formed by clusters of channels called ryanodine receptors on the sarcoplasmic reticulum (SR) within the cardiomyocyte. Distances between CRUs influence the diffusion of Ca2+, thus influencing the rate and strength of excitation-contraction coupling. Avian myocytes lack T-tubules, thus Ca2+ from surface CRUs (peripheral couplings, PCs), must diffuse to internal CRU sites of the corbular SR (cSR) during centripetal propagation. Despite this, avian hearts achieve higher contractile rates and develop greater contractile strength than many mammalian hearts, which have T-tubules to provide simultaneous activation of the Ca2+ signal through the myocyte. We used 3D electron tomography to test the hypothesis that the intracellular distribution of CRUs in the avian heart permits faster and stronger contractions despite the absence T-tubules. Nearest edge-edge distances between PCs and cSR, and geometric information including surface area and volumes of individual cSR, were obtained for each cardiac chamber of the White Leghorn chicken. Computational modelling was then used to establish a relationship between CRUs distances and cell activation time in the avian heart. Our data suggest that cSR clustered close together along the Z-line is vital for rapid propagation of the Ca2+ signal from the cell periphery to the cell centre which would aid in the strong and fast contractions of the avian heart.
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Affiliation(s)
- Thomas M. D. Sheard
- University of Manchester, Faculty of Biology, Medicine and Health, Oxford Road, Manchester, M13 9PL, UK
| | - Sanjay R. Kharche
- University of Manchester, Faculty of Biology, Medicine and Health, Oxford Road, Manchester, M13 9PL, UK
- Department of Medical Biophysics, University of Western Ontario, London, N6A 3K7, Canada
- Lawson Health Research Institute, 800 Commissioners Road East, London, Ontario, N6C 2R5, Canada
| | - Christian Pinali
- University of Manchester, Faculty of Biology, Medicine and Health, Oxford Road, Manchester, M13 9PL, UK
| | - Holly A. Shiels
- University of Manchester, Faculty of Biology, Medicine and Health, Oxford Road, Manchester, M13 9PL, UK
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Kharche SR, So A, Salerno F, Lee TY, Ellis C, Goldman D, McIntyre CW. Computational Assessment of Blood Flow Heterogeneity in Peritoneal Dialysis Patients' Cardiac Ventricles. Front Physiol 2018; 9:511. [PMID: 29867555 PMCID: PMC5968396 DOI: 10.3389/fphys.2018.00511] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Accepted: 04/20/2018] [Indexed: 01/28/2023] Open
Abstract
Dialysis prolongs life but augments cardiovascular mortality. Imaging data suggests that dialysis increases myocardial blood flow (BF) heterogeneity, but its causes remain poorly understood. A biophysical model of human coronary vasculature was used to explain the imaging observations, and highlight causes of coronary BF heterogeneity. Post-dialysis CT images from patients under control, pharmacological stress (adenosine), therapy (cooled dialysate), and adenosine and cooled dialysate conditions were obtained. The data presented disparate phenotypes. To dissect vascular mechanisms, a 3D human vasculature model based on known experimental coronary morphometry and a space filling algorithm was implemented. Steady state simulations were performed to investigate the effects of altered aortic pressure and blood vessel diameters on myocardial BF heterogeneity. Imaging showed that stress and therapy potentially increased mean and total BF, while reducing heterogeneity. BF histograms of one patient showed multi-modality. Using the model, it was found that total coronary BF increased as coronary perfusion pressure was increased. BF heterogeneity was differentially affected by large or small vessel blocking. BF heterogeneity was found to be inversely related to small blood vessel diameters. Simulation of large artery stenosis indicates that BF became heterogeneous (increase relative dispersion) and gave multi-modal histograms. The total transmural BF as well as transmural BF heterogeneity reduced due to large artery stenosis, generating large patches of very low BF regions downstream. Blocking of arteries at various orders showed that blocking larger arteries results in multi-modal BF histograms and large patches of low BF, whereas smaller artery blocking results in augmented relative dispersion and fractal dimension. Transmural heterogeneity was also affected. Finally, the effects of augmented aortic pressure in the presence of blood vessel blocking shows differential effects on BF heterogeneity as well as transmural BF. Improved aortic blood pressure may improve total BF. Stress and therapy may be effective if they dilate small vessels. A potential cause for the observed complex BF distributions (multi-modal BF histograms) may indicate existing large vessel stenosis. The intuitive BF heterogeneity methods used can be readily used in clinical studies. Further development of the model and methods will permit personalized assessment of patient BF status.
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Affiliation(s)
- Sanjay R Kharche
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada.,Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
| | - Aaron So
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada.,Robarts Research Institute, University of Western Ontario, London, ON, Canada
| | - Fabio Salerno
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada
| | - Ting-Yim Lee
- Robarts Research Institute, University of Western Ontario, London, ON, Canada
| | - Chris Ellis
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
| | - Daniel Goldman
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
| | - Christopher W McIntyre
- Kidney Clinical Research Unit, Lawson's Health Research Institute, Victoria Hospital, London, ON, Canada.,Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada
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Kharche SR, Vigmond E, Efimov IR, Dobrzynski H. Computational assessment of the functional role of sinoatrial node exit pathways in the human heart. PLoS One 2017; 12:e0183727. [PMID: 28873427 PMCID: PMC5584965 DOI: 10.1371/journal.pone.0183727] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2017] [Accepted: 08/09/2017] [Indexed: 11/19/2022] Open
Abstract
AIM The human right atrium and sinoatrial node (SAN) anatomy is complex. Optical mapping experiments suggest that the SAN is functionally insulated from atrial tissue except at discrete SAN-atrial electrical junctions called SAN exit pathways, SEPs. Additionally, histological imaging suggests the presence of a secondary pacemaker close to the SAN. We hypothesise that a) an insulating border-SEP anatomical configuration is related to SAN arrhythmia; and b) a secondary pacemaker, the paranodal area, is an alternate pacemaker but accentuates tachycardia. A 3D electro-anatomical computational model was used to test these hypotheses. METHODS A detailed 3D human SAN electro-anatomical mathematical model was developed based on our previous anatomical reconstruction. Electrical activity was simulated using tissue specific variants of the Fenton-Karma action potential equations. Simulation experiments were designed to deploy this complex electro-anatomical system to assess the roles of border-SEPs and paranodal area by mimicking experimentally observed SAN arrhythmia. Robust and accurate numerical algorithms were implemented for solving the mono domain reaction-diffusion equation implicitly, calculating 3D filament traces, and computing dominant frequency among other quantitative measurements. RESULTS A centre to periphery gradient of increasing diffusion was sufficient to permit initiation of pacemaking at the centre of the 3D SAN. Re-entry within the SAN, micro re-entry, was possible by imposing significant SAN fibrosis in the presence of the insulating border. SEPs promoted the micro re-entry to generate more complex SAN-atrial tachycardia. Simulation of macro re-entry, i.e. re-entry around the SAN, was possible by inclusion of atrial fibrosis in the presence of the insulating border. The border shielded the SAN from atrial tachycardia. However, SAN micro-structure intercellular gap junctional coupling and the paranodal area contributed to prolonged atrial fibrillation. Finally, the micro-structure was found to be sufficient to explain shifts of leading pacemaker site location. CONCLUSIONS The simulations establish a relationship between anatomy and SAN electrical function. Microstructure, in the form of intercellular gap junction coupling, was found to regulate SAN function and arrhythmia.
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Affiliation(s)
- Sanjay R. Kharche
- Institute of Cardiovascular Sciences, School of Medical Sciences, University of Manchester, Manchester, United Kingdom
| | - Edward Vigmond
- University of Bordeaux, IMB, UMR 5251, Talence, France
- IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Pessac- Bordeaux, France
| | - Igor R. Efimov
- Department of Biomedical Engineering, The George Washington University, Washington, DC, United States of America
| | - Halina Dobrzynski
- Institute of Cardiovascular Sciences, School of Medical Sciences, University of Manchester, Manchester, United Kingdom
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Atkinson AJ, Kharche SR, Bateman MG, Iaizzo PA, Dobrzynski H. 3D anatomical reconstruction of human cardiac conduction system and simulation of bundle branch block after TAVI procedure. Annu Int Conf IEEE Eng Med Biol Soc 2017; 2016:5583-5586. [PMID: 28269520 DOI: 10.1109/embc.2016.7591992] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The cardiac conduction system (CCS) is responsible for the initiation and propagation of action potentials through the heart ensuring efficient pumping of blood. Understanding the anatomy of the CCS and its relationship with other major cardiac components is important to help understand arrhythmias and how certain procedures may increase the incidence of arrhythmias developing. We sectioned a whole human heart and performed Masson's trichrome histology in order to identify the components of the CCS. The histology images were used to construct a 3D anatomical model. We have shown that it is possible to create a 3D anatomical model of the human heart incorporating the CCS based on histological images, and that this model can be used to perform computer simulations of cardiac excitation. From the reconstruction we have been able to show the relative positions of the CCS components to each other. We have also shown how the close proximity of the CCS to the aortic valve can explain some of the conduction complications, such as left bundle branch block, that arise after aortic valve replacement procedures.
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Logantha SJRJ, Stokke MK, Atkinson AJ, Kharche SR, Parveen S, Saeed Y, Sjaastad I, Sejersted OM, Dobrzynski H. Ca(2+)-Clock-Dependent Pacemaking in the Sinus Node Is Impaired in Mice with a Cardiac Specific Reduction in SERCA2 Abundance. Front Physiol 2016; 7:197. [PMID: 27313537 PMCID: PMC4889599 DOI: 10.3389/fphys.2016.00197] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 05/17/2016] [Indexed: 12/23/2022] Open
Abstract
Background: The sarcoplasmic reticulum Ca2+-ATPase (SERCA2) pump is an important component of the Ca2+-clock pacemaker mechanism that provides robustness and flexibility to sinus node pacemaking. We have developed transgenic mice with reduced cardiac SERCA2 abundance (Serca2 KO) as a model for investigating SERCA2's role in sinus node pacemaking. Methods and Results: In Serca2 KO mice, ventricular SERCA2a protein content measured by Western blotting was 75% (P < 0.05) lower than that in control mice (Serca2 FF) tissue. Immunofluorescent labeling of SERCA2a in ventricular, atrial, sinus node periphery and center tissue sections revealed 46, 45, 55, and 34% (all P < 0.05 vs. Serca2 FF) lower labeling, respectively and a mosaic pattern of expression. With telemetric ECG surveillance, we observed no difference in basal heart rate, but the PR-interval was prolonged in Serca2 KO mice: 49 ± 1 vs. 40 ± 1 ms (P < 0.001) in Serca2 FF. During exercise, heart rate in Serca2 KO mice was elevated to 667 ± 22 bpm, considerably less than 780 ± 17 bpm (P < 0.01) in Serca2 FF. In isolated sinus node preparations, 2 mM Cs+ caused bradycardia that was equally pronounced in Serca2 KO and Serca2 FF (32 ± 4% vs. 29 ± 5%), indicating no change in the pacemaker current, If. Disabling the Ca2+-clock with 2 μM ryanodine induced bradycardia that was less pronounced in Serca2 KO preparations (9 ± 1% vs. 20 ± 3% in Serca2 FF; P < 0.05), suggesting a disrupted Ca2+-clock. Mathematical modeling was used to dissect the effects of membrane- and Ca2+-clock components on Serca2 KO mouse heart rate and sinus node action potential. Computer modeling predicted a slowing of heart rate with SERCA2 downregulation and the heart rate slowing was pronounced at >70% reduction in SERCA2 activity. Conclusions:Serca2 KO mice show a disrupted Ca2+-clock-dependent pacemaker mechanism contributing to impaired sinus node and atrioventricular node function.
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Affiliation(s)
| | - Mathis K Stokke
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway; Clinic for Internal Medicine, Lovisenberg Deaconess Hospital ASOslo, Norway
| | - Andrew J Atkinson
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Sanjay R Kharche
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Sajida Parveen
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Yawer Saeed
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway
| | - Ole M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of OsloOslo, Norway; Center for Heart Failure Research, University of OsloOslo, Norway
| | - Halina Dobrzynski
- Institute of Cardiovascular Sciences, University of Manchester Manchester, UK
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Moreno C, de la Cruz A, Oliveras A, Kharche SR, Guizy M, Comes N, Starý T, Ronchi C, Rocchetti M, Baró I, Loussouarn G, Zaza A, Severi S, Felipe A, Valenzuela C. Marine n-3 PUFAs modulate IKs gating, channel expression, and location in membrane microdomains. Cardiovasc Res 2014; 105:223-32. [PMID: 25497550 DOI: 10.1093/cvr/cvu250] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS Polyunsaturated fatty n-3 acids (PUFAs) have been reported to exhibit antiarrhythmic properties. However, the mechanisms of action remain unclear. We studied the electrophysiological effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on IKs, and on the expression and location of Kv7.1 and KCNE1. METHODS AND RESULTS Experiments were performed using patch-clamp, western blot, and sucrose gradient techniques in COS7 cells transfected with Kv7.1/KCNE1 channels. Acute perfusion with both PUFAs increased Kv7.1/KCNE1 current, this effect being greater for DHA than for EPA. Similar results were found in guinea pig cardiomyocytes. Acute perfusion of either PUFA slowed the activation kinetics and EPA shifted the activation curve to the left. Conversely, chronic EPA did not modify Kv7.1/KCNE1 current magnitude and shifted the activation curve to the right. Chronic PUFAs decreased the expression of Kv7.1, but not of KCNE1, and induced spatial redistribution of Kv7.1 over the cell membrane. Cholesterol depletion with methyl-β-cyclodextrin increased Kv7.1/KCNE1 current magnitude. Under these conditions, acute EPA produced similar effects than those induced in non-cholesterol-depleted cells. A ventricular action potential computational model suggested antiarrhythmic efficacy of acute PUFA application under IKr block. CONCLUSIONS We provide evidence that acute application of PUFAs increases Kv7.1/KCNE1 through a probably direct effect, and shows antiarrhythmic efficacy under IKr block. Conversely, chronic EPA application modifies the channel activity through a change in the Kv7.1/KCNE1 voltage-dependence, correlated with a redistribution of Kv7.1 over the cell membrane. This loss of function may be pro-arrhythmic. This shed light on the controversial effects of PUFAs regarding arrhythmias.
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Affiliation(s)
- Cristina Moreno
- Instituto de Investigaciones Biomédicas 'Alberto Sols' CSIC-UAM, C/Arturo Duperier 4, 28029 Madrid, Spain
| | - Alicia de la Cruz
- Instituto de Investigaciones Biomédicas 'Alberto Sols' CSIC-UAM, C/Arturo Duperier 4, 28029 Madrid, Spain
| | - Anna Oliveras
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
| | - Sanjay R Kharche
- Biomedical Engineering Laboratory D.E.I.S., University of Bologna, 47521 Cesena, Italy
| | - Miriam Guizy
- Instituto de Investigaciones Biomédicas 'Alberto Sols' CSIC-UAM, C/Arturo Duperier 4, 28029 Madrid, Spain
| | - Nùria Comes
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
| | - Tomáš Starý
- Biomedical Engineering Laboratory D.E.I.S., University of Bologna, 47521 Cesena, Italy
| | - Carlotta Ronchi
- Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Marcella Rocchetti
- Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Isabelle Baró
- L'Institut du Thorax, Unité Inserm UMR 1087/CNRS UMR 6291, Nantes, France
| | - Gildas Loussouarn
- L'Institut du Thorax, Unité Inserm UMR 1087/CNRS UMR 6291, Nantes, France
| | - Antonio Zaza
- Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy
| | - Stefano Severi
- Biomedical Engineering Laboratory D.E.I.S., University of Bologna, 47521 Cesena, Italy
| | - Antonio Felipe
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
| | - Carmen Valenzuela
- Instituto de Investigaciones Biomédicas 'Alberto Sols' CSIC-UAM, C/Arturo Duperier 4, 28029 Madrid, Spain
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Kharche SR, Stary T, Colman MA, Biktasheva IV, Workman AJ, Rankin AC, Holden AV, Zhang H. Effects of human atrial ionic remodelling by β-blocker therapy on mechanisms of atrial fibrillation: a computer simulation. Europace 2014; 16:1524-33. [PMID: 25085203 DOI: 10.1093/europace/euu084] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS Atrial anti-arrhythmic effects of β-adrenoceptor antagonists (β-blockers) may involve both a suppression of pro-arrhythmic effects of catecholamines, and an adaptational electrophysiological response to chronic β-blocker use; so-called 'pharmacological remodelling'. In human atrium, such remodelling decreases the transient outward (Ito) and inward rectifier (IK1) K(+) currents, and increases the cellular action potential duration (APD) and effective refractory period (ERP). However, the consequences of these changes on mechanisms of genesis and maintenance of atrial fibrillation (AF) are unknown. Using mathematical modelling, we tested the hypothesis that the long-term adaptational decrease in human atrial Ito and IK1 caused by chronic β-blocker therapy, i.e. independent of acute electrophysiological effects of β-blockers, in an otherwise un-remodelled atrium, could suppress AF. METHODS AND RESULTS Contemporarily, biophysically detailed human atrial cell and tissue models were used to investigate effects of the β-blocker-based pharmacological remodelling. Chronic β-blockade remodelling prolonged atrial cell APD and ERP. The incidence of small amplitude APD alternans in the CRN model was reduced. At the 1D tissue level, β-blocker remodelling decreased the maximum pacing rate at which APs could be conducted. At the three-dimensional organ level, β-blocker remodelling reduced the life span of re-entry scroll waves. CONCLUSION This study improves our understanding of the electrophysiological mechanisms of AF suppression by chronic β-blocker therapy. Atrial fibrillation suppression may involve a reduced propensity for maintenance of re-entrant excitation waves, as a consequence of increased APD and ERP.
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Affiliation(s)
- Sanjay R Kharche
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - Tomas Stary
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK
| | - Michael A Colman
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - Irina V Biktasheva
- Department of Computer Sciences, University of Liverpool, Liverpool, L69 3BX, UK
| | - Antony J Workman
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK
| | - Andrew C Rankin
- School of Medicine, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Arun V Holden
- School of Biomedical Sciences, University of Leeds, Leeds, LS6 9JT, UK
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
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14
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Kharche SR, Biktasheva IV, Zhang H, Biktashev VN. Simulating the role of anisotropy in human atrial cardioversion. Annu Int Conf IEEE Eng Med Biol Soc 2013; 2013:6838-41. [PMID: 24111315 DOI: 10.1109/embc.2013.6611128] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
This computational study quantifies the effectiveness of feedback controlled low energy cardioversion in the anisotropic human atria. An established biophysical human cell model was adopted to reproduce Control and chronic atrial fibrillation (CAF) action potentials. The cell model was combined with a detailed human atrial geometry to construct a 3D realistic human atrial model. Scroll waves were simulated under Control and CAF conditions and the cardioversion parameters of stimulation strength and pacing duration were evaluated for scroll wave termination. Scroll waves were initiated at two locations in the atria to elicit the effects of scroll wave location. The role of anisotropy was highlighted by comparison to results from the isotropic case. Under Control conditions, scroll wave self-termination was rapid in the anisotropic case. Under CAF conditions, anisotropy caused the initiated scroll wave to degenerate into multiple scrolls with each evolving erratically or pinning to anatomical defects. The cardioversion successfully terminated scroll waves within 10 s, but the stimulus strength had a strong correlation to the location of the scroll wave. The low energy stimulation strength was always lower than the threshold stimulus. Anisotropy plays an important role in atrial electrical properties. Anisotropy aggravates CAF and leads to high frequency atrial pacing. The efficacy of cardioversion is significantly affected by anisotropy.
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