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Kulkarni K, Pallares-Lupon N, Armoundas AA, Pasdois P, Bernus O, Walton RD. Investigating Electrophysiological Markers of Arrhythmogenesis in a Chronic Myocardial Infarction Ovine Model. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2022; 2022:657-661. [PMID: 36086483 DOI: 10.1109/embc48229.2022.9871496] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Cardiac alternans has been associated with an increased propensity to lethal tachyarrhythmias such as ventricular tachycardia and fibrillation (VT/VF). Myocardial infarction (MI), resulting from restricted oxygen supply to the heart, is a known substrate for VT/VF. Here, we investigate the utility of cardiac alternans as a predictor of tachyarrhythmias in a chronic MI ovine model. In-vivo electrophysiological studies were performed to assess the change in microvolt T-wave alternans (TWA) with induction of acute ischemia following coronary artery occlusion. 24-hour telemetry was performed in an ambulatory animal for 6 weeks to monitor the progression of TWA with chronic MI. At 6 weeks, ex-vivo optical mapping experiments were performed to assess the spatiotemporal evolution of alternans in sham (n=5) and chronic MI hearts (n=8). Our results demonstrate that chronic MI leads to significant electrophysiological changes in the cardiac substrate. Significant increase in TWA is observed post occlusion and a steady rise in alternans is seen with progression of chronic MI. Compared to sham, chronic MI hearts show significant presence of localized action potential amplitude alternans, which spatially evolve with an increase in pacing frequency. Clinical Relevance - Our results demonstrate that localized alternans underlie arrhythmogenesis in chronic MI hearts and microvolt TWA can serve as a biomarker of disease progression during chronic MI.
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Merchant FM, Sayadi O, Sohn K, Weiss EH, Puppala D, Doddamani R, Singh JP, Heist EK, Owen C, Kulkarni K, Armoundas AA. Real-Time Closed-Loop Suppression of Repolarization Alternans Reduces Arrhythmia Susceptibility In Vivo. Circ Arrhythm Electrophysiol 2020; 13:e008186. [PMID: 32434448 DOI: 10.1161/circep.119.008186] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. METHODS We have developed a real-time, closed-loop system to record and analyze RA from multiple intracardiac leads, and deliver dynamically R-wave triggered pacing stimuli during the absolute refractory period. We have evaluated the ability of this system to control RA and reduce arrhythmia susceptibility, in vivo. RESULTS R-wave triggered pacing can induce RA, the magnitude of which can be modulated by varying the amplitude, pulse width, and size of the pacing vector. Using a swine model (n=9), we demonstrate that to induce a 1 µV change in the alternans voltage on the body surface, coronary sinus and left ventricle leads, requires a delivered charge of 0.04±0.02, 0.05±0.025, and 0.06±0.033 µC, respectively, while to induce a one unit change of the Kscore, requires a delivered charge of 0.93±0.73, 0.32±0.29, and 0.33±0.37 µC, respectively. For all body surface and intracardiac leads, both Δ(alternans voltage) and ΔKscore between baseline and R-wave triggered paced beats increases consistently with an increase in the pacing pulse amplitude, pulse width, and vector spacing. Additionally, we show that the proposed method can be used to suppress spontaneously occurring alternans (n=7), in the presence of myocardial ischemia. Suppression of RA by pacing during the absolute refractory period results in a significant reduction in arrhythmia susceptibility, evidenced by a lower Srank score during programmed ventricular stimulation compared with baseline before ischemia. CONCLUSIONS We have developed and evaluated a novel closed-loop method to dynamically modulate RA in a swine model. Our data suggest that suppression of RA directly reduces arrhythmia susceptibility and reinforces the concept that RA plays a critical role in the pathophysiology of arrhythmogenesis.
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Affiliation(s)
- Faisal M Merchant
- Cardiology Division, Emory University School of Medicine, Atlanta, GA (F.M.M.).,Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Omid Sayadi
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Kwanghyun Sohn
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Eric H Weiss
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston.,Institute for Medical Engineering and Science, Massachusetts Institute of Technology Cambridge (E.H.W., A.A.A.)
| | - Dheeraj Puppala
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Rajiv Doddamani
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Jagmeet P Singh
- Cardiology Division, Cardiac Arrhythmia Service (J.P.S., E.K.H.), Massachusetts General Hospital, Boston
| | - E Kevin Heist
- Cardiology Division, Cardiac Arrhythmia Service (J.P.S., E.K.H.), Massachusetts General Hospital, Boston
| | - Chris Owen
- Neurosurgery Division (C.O.), Massachusetts General Hospital, Boston
| | - Kanchan Kulkarni
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston
| | - Antonis A Armoundas
- Cardiovascular Research Center (F.M.M., O.S., K.S., E.H.W., D.P., R.D., K.K., A.A.A.), Massachusetts General Hospital, Boston.,Institute for Medical Engineering and Science, Massachusetts Institute of Technology Cambridge (E.H.W., A.A.A.)
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Hsieh YC, Hsieh WH, Li CH, Liao YC, Lin JC, Weng CJ, Lo MT, Tuan TC, Lin SF, Yeh HI, Huang JL, Haugan K, Larsen BD, Lin YJ, Lin WW, Wu TJ, Chen SA. Ventricular divergence correlates with epicardial wavebreaks and predicts ventricular arrhythmia in isolated rabbit hearts during therapeutic hypothermia. PLoS One 2020; 15:e0228818. [PMID: 32084145 PMCID: PMC7034916 DOI: 10.1371/journal.pone.0228818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Accepted: 01/23/2020] [Indexed: 11/19/2022] Open
Abstract
INTRODUCTION High beat-to-beat morphological variation (divergence) on the ventricular electrogram during programmed ventricular stimulation (PVS) is associated with increased risk of ventricular fibrillation (VF), with unclear mechanisms. We hypothesized that ventricular divergence is associated with epicardial wavebreaks during PVS, and that it predicts VF occurrence. METHOD AND RESULTS Langendorff-perfused rabbit hearts (n = 10) underwent 30-min therapeutic hypothermia (TH, 30°C), followed by a 20-min treatment with rotigaptide (300 nM), a gap junction modifier. VF inducibility was tested using burst ventricular pacing at the shortest pacing cycle length achieving 1:1 ventricular capture. Pseudo-ECG (p-ECG) and epicardial activation maps were simultaneously recorded for divergence and wavebreaks analysis, respectively. A total of 112 optical and p-ECG recordings (62 at TH, 50 at TH treated with rotigaptide) were analyzed. Adding rotigaptide reduced ventricular divergence, from 0.13±0.10 at TH to 0.09±0.07 (p = 0.018). Similarly, rotigaptide reduced the number of epicardial wavebreaks, from 0.59±0.73 at TH to 0.30±0.49 (p = 0.036). VF inducibility decreased, from 48±31% at TH to 22±32% after rotigaptide infusion (p = 0.032). Linear regression models showed that ventricular divergence correlated with epicardial wavebreaks during TH (p<0.001). CONCLUSION Ventricular divergence correlated with, and might be predictive of epicardial wavebreaks during PVS at TH. Rotigaptide decreased both the ventricular divergence and epicardial wavebreaks, and reduced the probability of pacing-induced VF during TH.
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Affiliation(s)
- Yu-Cheng Hsieh
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Department of Data Science and Big Data Analytics and Department of Financial Engineering, Providence University, Taichung, Taiwan
- * E-mail:
| | - Wan-Hsin Hsieh
- Biomedical Technology and Device Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
| | - Cheng-Hung Li
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Department of Data Science and Big Data Analytics and Department of Financial Engineering, Providence University, Taichung, Taiwan
| | - Ying-Chieh Liao
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Department of Data Science and Big Data Analytics and Department of Financial Engineering, Providence University, Taichung, Taiwan
| | - Jiunn-Cherng Lin
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Department of Data Science and Big Data Analytics and Department of Financial Engineering, Providence University, Taichung, Taiwan
| | - Chi-Jen Weng
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Department of Data Science and Big Data Analytics and Department of Financial Engineering, Providence University, Taichung, Taiwan
| | - Men-Tzung Lo
- Research Center for Adaptive Data Analysis, National Central University, Jhongli City, Taiwan
| | - Ta-Chuan Tuan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Shien-Fong Lin
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, United States of America
- Institute of Biomedical Engineering, National Chiao-Tung University, Hsinchu, Taiwan
| | - Hung-I Yeh
- Departments of Internal Medicine and Medical Research, Mackay Memorial Hospital, Mackay Medical College, New Taipei City, Taiwan
| | - Jin-Long Huang
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
| | - Ketil Haugan
- Department of Cardiology, Zealand University Hospital, Roskilde, Denmark
| | | | - Yenn-Jiang Lin
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Wei-Wen Lin
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Life Science, Tunghai University, Taichung, Taiwan
| | - Tsu-Juey Wu
- Cardiovascular Center, Taichung Veterans General Hospital and Chiayi Branch, Taichung and Chiayi, Taiwan
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
| | - Shih-Ann Chen
- Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei, Taiwan
- Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan
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Kulkarni K, Merchant FM, Kassab MB, Sana F, Moazzami K, Sayadi O, Singh JP, Heist EK, Armoundas AA. Cardiac Alternans: Mechanisms and Clinical Utility in Arrhythmia Prevention. J Am Heart Assoc 2019; 8:e013750. [PMID: 31617437 PMCID: PMC6898836 DOI: 10.1161/jaha.119.013750] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Kanchan Kulkarni
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
| | | | - Mohamad B. Kassab
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
| | - Furrukh Sana
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
| | - Kasra Moazzami
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
| | - Omid Sayadi
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
| | - Jagmeet P. Singh
- Cardiology DivisionCardiac Arrhythmia ServiceMassachusetts General HospitalBostonMA
| | - E. Kevin Heist
- Cardiology DivisionCardiac Arrhythmia ServiceMassachusetts General HospitalBostonMA
| | - Antonis A. Armoundas
- Cardiovascular Research CenterMassachusetts General HospitalBostonMA
- Institute for Medical Engineering and ScienceMassachusetts Institute of TechnologyCambridgeMA
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Guevara MR, Shrier A, Orlowski J, Glass L. George Ralph Mines (1886-1914): the dawn of cardiac nonlinear dynamics. J Physiol 2016; 594:2361-71. [PMID: 27126414 DOI: 10.1113/jp270891] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 01/29/2016] [Indexed: 11/08/2022] Open
Affiliation(s)
- Michael R Guevara
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Alvin Shrier
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - John Orlowski
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Leon Glass
- Department of Physiology, McGill University, Montreal, Quebec, Canada
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Merchant FM, Sayadi O, Moazzami K, Puppala D, Armoundas AA. T-wave alternans as an arrhythmic risk stratifier: state of the art. Curr Cardiol Rep 2014; 15:398. [PMID: 23881581 DOI: 10.1007/s11886-013-0398-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Microvolt level T-wave alternans (MTWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an increased risk of ventricular tachyarrhythmic events (VTE) and sudden cardiac death (SCD) during medium- and long-term follow-up. Recent observations also suggest that heightened MTWA magnitude may be closely associated with short-term risk of impending VTE. At the subcellular and cellular level, perturbations in calcium transport processes likely play a primary role in the genesis of alternans, which then secondarily lead to alternans of action potential morphology and duration (APD). As such, MTWA may play a role not only in risk stratification but also more fundamentally in the pathogenesis of VTE. In this paper, we outline recent advances in understanding the pathogenesis of MTWA and also the utility of T-wave alternans testing for clinical risk stratification. We also highlight emerging clinical applications for MTWA.
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Affiliation(s)
- Faisal M Merchant
- Cardiology Division, Emory University School of Medicine, Atlanta, GA, USA
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7
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Merchant FM, Armoundas AA. Role of substrate and triggers in the genesis of cardiac alternans, from the myocyte to the whole heart: implications for therapy. Circulation 2012; 125:539-49. [PMID: 22271847 DOI: 10.1161/circulationaha.111.033563] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Faisal M Merchant
- Cardiology Division, Emory University School of Medicine, Atlanta, GA, USA
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8
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Weiss EH, Merchant FM, d'Avila A, Foley L, Reddy VY, Singh JP, Mela T, Ruskin JN, Armoundas AA. A novel lead configuration for optimal spatio-temporal detection of intracardiac repolarization alternans. Circ Arrhythm Electrophysiol 2011; 4:407-17. [PMID: 21430127 DOI: 10.1161/circep.109.934208] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Electric alternans is a pattern of variation in the shape of ECG waveform that occurs every other beat. In humans, alternation in ventricular repolarization, known as repolarization alternans (RA), has been associated with increased vulnerability to ventricular tachycardia/fibrillation and sudden cardiac death. METHODS AND RESULTS This study investigates the spatio-temporal variability of intracardiac RA and its relationship to body surface RA in an acute myocardial ischemia model in swine. We developed a real-time multichannel repolarization signal acquisition, display, and analysis system to record ECG signals from catheters in the right ventricle, coronary sinus, left ventricle, and epicardial surface before and after circumflex coronary artery balloon occlusion. We found that RA is detectable within 4 minutes after the onset ischemia and is most prominently seen during the first half of the repolarization interval. Ischemia-induced RA was detectable on unipolar and bipolar leads (both in near- and far-field configurations) and on body surface leads. Far-field bipolar intracardiac leads were more sensitive for RA detection than body surface leads, with the probability of body surface RA detection increasing as the number of intracardiac leads detecting RA increased, approaching 100% when at least three intracardiac leads detected RA. We developed a novel, clinically applicable intracardiac lead system based on a triangular arrangement of leads spanning the right ventricular and coronary sinus catheters, which provided the highest sensitivity for intracardiac RA detection when compared with any other far-field bipolar sensing configurations. CONCLUSIONS In conclusion, intracardiac alternans, a complex spatio-temporal phenomenon associated with arrhythmia susceptibility and sudden cardiac death, can be reliably detected through a novel triangular right ventricular-coronary sinus lead configuration.
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Affiliation(s)
- Eric H Weiss
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, USA
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Garzón A, Grigoriev RO, Fenton FH. Model-based control of cardiac alternans on a ring. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:021932. [PMID: 19792176 DOI: 10.1103/physreve.80.021932] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2008] [Revised: 05/11/2009] [Indexed: 05/08/2023]
Abstract
Cardiac alternans, a beat-to-beat alternation of cardiac electrical dynamics, and ventricular tachycardia, generally associated with a spiral wave of electrical activity, have been identified as frequent precursors of the life-threatening spatiotemporally chaotic electrical state of ventricular fibrillation (VF). Schemes for the elimination of alternans and the stabilization of spiral waves through the injection of weak external currents have been proposed as methods to prevent VF but have not performed at the level required for clinical implementation. In this paper we propose a control method based on linear-quadratic regulator (LQR) control. Unlike most previously proposed approaches, our method incorporates information from the underlying model to increase efficiency. We use a one-dimensional ringlike geometry, with a single control electrode, to compare the performance of our method with that of two other approaches, quasi-instantaneous suppression of unstable modes (QISUM) and time-delay autosynchronization (TDAS). We find that QISUM fails to suppress alternans due to conduction block. Although both TDAS and LQR succeed in suppressing alternans, LQR is able to suppress the alternans faster and using a much weaker control current. Our results highlight the benefits of a model-based control approach despite its inherent complexity compared with nonmodel-based control such as TDAS.
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Affiliation(s)
- Alejandro Garzón
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA
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López A, Arce H, Guevara MR. Rhythms of high-grade block in an ionic model of a strand of regionally ischemic ventricular muscle. J Theor Biol 2007; 249:29-45. [PMID: 17706682 DOI: 10.1016/j.jtbi.2007.06.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2006] [Revised: 06/11/2007] [Accepted: 06/11/2007] [Indexed: 11/15/2022]
Abstract
Electrical alternans, a beat-to-beat alternation in the electrocardiogram or electrogram, is frequently seen during the first few minutes of acute myocardial ischemia, and is often immediately followed by malignant cardiac arrhythmias such as ventricular tachycardia and ventricular fibrillation. As ischemia progresses, higher-order periodic rhythms (e.g., period-4) can replace the period-2 alternans rhythm. This is also seen in modelling work on a two-dimensional (2-D) sheet of regionally ischemic ventricular muscle. In addition, in the experimental work, ventricular arrhythmias are overwhelmingly seen only after the higher-order rhythms arise. We investigate an ionic model of a strand of ischemic ventricular muscle, constructed as a 3-cm-long 1-D cable with a centrally located 1-cm-long segment exposed to an elevated extracellular potassium concentration ([K(+)](o)). As [K(+)](o) is raised in this "ischemic segment" to represent one major effect of ongoing ischemia, the sequence of rhythms {1:1-->2:2 (alternans)-->2:1} is seen. With further increase in [K(+)](o), one sees higher-order periodic 2N:M rhythms {2:1-->4:2-->4:1-->6:2-->6:1-->8:2-->8:1}. In a 2N:M cycle, only M of the 2N action potentials generated at the proximal end of the cable successfully traverse the ischemic segment, with the remaining ones being blocked within the ischemic segment. Finally, there is a transition to complete block {8:1-->2:0-->1:0} (in an n:0 rhythm, all action potentials die out within the ischemic segment). Changing the length of the ischemic segment results in different rhythms and transitions being seen: e.g., when the ischemic segment is 2 cm long, the period-6 rhythms are not seen; when it is 0.5 cm long, there is a 3:1 rhythm interposed between the 2:1 and 1:0 rhythms. We discuss the relevance of our results to the experimental observations on the higher-order rhythms that presage reentrant ischemic ventricular arrhythmias.
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Affiliation(s)
- Alejandro López
- Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, 04510 México, Distrito Federal, México
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11
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Krogh-Madsen T, Christini DJ. Action potential duration dispersion and alternans in simulated heterogeneous cardiac tissue with a structural barrier. Biophys J 2006; 92:1138-49. [PMID: 17114216 PMCID: PMC1783878 DOI: 10.1529/biophysj.106.090845] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Structural barriers to wave propagation in cardiac tissue are associated with a decreased threshold for repolarization alternans both experimentally and clinically. Using computer simulations, we investigated the effects of a structural barrier on the onset of spatially concordant and discordant alternans. We used two-dimensional tissue geometry with heterogeneity in selected potassium conductances to mimic known apex-base gradients. Although we found that the actual onset of alternans was similar with and without the structural barrier, the increase in alternans magnitude with faster pacing was steeper with the barrier--giving the appearance of an earlier alternans onset in its presence. This is consistent with both experimental structural barrier findings and the clinical observation of T-wave alternans occurring at slower pacing rates in patients with structural heart disease. In ionically homogeneous tissue, discordant alternans induced by the presence of the structural barrier arose at intermediate pacing rates due to a source-sink mismatch behind the barrier. In heterogeneous tissue, discordant alternans occurred during fast pacing due to a barrier-induced decoupling of tissue with different restitution properties. Our results demonstrate a causal relationship between the presence of a structural barrier and increased alternans magnitude and action potential duration dispersion, which may contribute to why patients with structural heart disease are at higher risk for ventricular tachyarrhythmias.
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Affiliation(s)
- Trine Krogh-Madsen
- Department of Medicine, Division of Cardiology, Weill Medical College of Cornell University, New York, New York 10021, USA
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12
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Jordan PN, Christini DJ. Action potential morphology influences intracellular calcium handling stability and the occurrence of alternans. Biophys J 2005; 90:672-80. [PMID: 16239324 PMCID: PMC1367072 DOI: 10.1529/biophysj.105.071340] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Instability in the intracellular Ca2+ handling system leading to Ca2+ alternans is hypothesized to be an underlying cause of electrical alternans. The highly coupled nature of membrane voltage and Ca2+ regulation suggests that there should be reciprocal effects of membrane voltage on the stability of the Ca2+ handling system. We investigated such effects using a mathematical model of the cardiac intracellular Ca2+ handling system. We found that the morphology of the action potential has a significant effect on the stability of the Ca2+ handling system at any given pacing rate, with small changes in action potential morphology resulting in a transition from stable nonalternating Ca2+ transients to stable alternating Ca2+ transients. This bifurcation occurs as the alternans eigen value of the system changes from absolute value <1 to absolute value >1. These results suggest that the stability of the intracellular Ca2+ handling system and the occurrence of Ca2+ alternans are not dictated solely by the Ca2+ handling system itself, but are also modulated to a significant degree by membrane voltage (through its influence on sarcolemmal Ca2+ currents) and, therefore, by all ionic currents that affect membrane voltage.
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Affiliation(s)
- Peter N Jordan
- Department of Physiology and Biophysics, Weill Graduate School of Medical Sciences of Cornell University, New York, New York, 10021, USA
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Lakireddy V, Baweja P, Syed A, Bub G, Boutjdir M, El-Sherif N. Contrasting effects of ischemia on the kinetics of membrane voltage and intracellular calcium transient underlie electrical alternans. Am J Physiol Heart Circ Physiol 2005; 288:H400-7. [PMID: 15345492 DOI: 10.1152/ajpheart.00502.2004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Repolarization alternans has been considered a strong marker of electrical instability. The objective of this study was to investigate the hypothesis that ischemia-induced contrasting effects on the kinetics of membrane voltage and intracellular calcium transient (CaiT) can explain the vulnerability of the ischemic heart to repolarization alternans. Ischemia-induced changes in action potential (AP) and CaiT resulting in alternans were investigated in perfused Langendorff guinea pig hearts subjected to 10–15 min of global no-flow ischemia followed by 10–15 min of reperfusion. The heart was stained with 100 μl of rhod-2 AM and 25 μl of RH-237, and AP and CaiT were simultaneously recorded with an optical mapping system of two 16 × 16 photodiode arrays. Ischemia was associated with shortening of AP duration (D) but delayed upstroke, broadening of peak, and slowed decay of CaiT resulting in a significant increase of CaiT-D. The changes in APD were spatially heterogeneous in contrast to a more spatially homogeneous lengthening of CaiT-D. CaiT alternans could be consistently induced with the introduction of a shorter cycle when the upstroke of the AP occurred before complete relaxation of the previous CaiT and generated a reduced CaiT. However, alternans of CaiT was not necessarily associated with alternans of APD, and this was correlated with the degree of spatially heterogeneous shortening of APD. Sites with less shortening of APD developed alternans of both CaiT and APD, whereas sites with greater shortening of APD could develop a similar degree of CaiT alternans but slight or no APD alternans. This resulted in significant spatial dispersion of APD. The study shows that the contrasting effects of ischemia on the duration of AP and CaiT and, in particular, on their spatial distribution explain the vulnerability of ischemic heart to alternans and the increased dispersion of repolarization during alternans.
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Affiliation(s)
- Vikram Lakireddy
- New York Harbor Veterans Affairs Healthcare System and Downstate Medical Center, State University of New York, 450 Clarkson Ave., Box 1199, Brooklyn, NY 11203, USA
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Jordan PN, Christini DJ. Adaptive Diastolic Interval Control of Cardiac Action Potential Duration Alternans. J Cardiovasc Electrophysiol 2004; 15:1177-85. [PMID: 15485444 DOI: 10.1046/j.1540-8167.2004.04098.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
INTRODUCTION Recent experimental and computational studies have shown that beat-to-beat alternation in action potential duration can trigger cardiac reentry, suggesting that such "alternans" is a mechanistic precursor to arrhythmias. Given such a link, termination of alternans may help prevent the onset of arrhythmias. To this end, recent efforts have shown that chaos control methods can modulate the timing of electrical stimulation to eliminate alternans. METHODS AND RESULTS We have developed an alternative control method founded entirely in cardiac electrophysiology (rather than borrowing techniques from the control of physical systems as with existing control techniques). Using computer simulations, we show that this method, which exploits the rate-dependent behavior of cardiac tissue, can be used to control alternans (and higher-order) rhythms, and is robust to drift and noise. When applied to individual model cells exhibiting alternans, the algorithm converges to the period-1 rhythm over as wide, and in some cases a wider, range of feedback proportionality constant values relative to existing methods. Control success comparable to existing methods is achieved when the algorithm is applied to a simulated one-dimensional Purkinje fiber exhibiting alternans. CONCLUSION We have developed a method that adaptively controls the timing of electrical stimulation to rapidly eliminate action potential duration alternans in cardiac tissue. This control method may prove valuable in future arrhythmia prevention therapies.
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Affiliation(s)
- Peter N Jordan
- Department of Physiology and Biophysics, Weill Graduate School of Medical Sciences of Cornell University, New York, New York 10021, USA
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Jordan PN, Christini DJ. Determining the effects of memory and action potential duration alternans on cardiac restitution using a constant-memory restitution protocol. Physiol Meas 2004; 25:1013-24. [PMID: 15382838 DOI: 10.1088/0967-3334/25/4/018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Restitution, the dependence of action potential duration (APD) on diastolic interval, may be causally linked to the vulnerability of cardiac tissue to certain types of arrhythmias. While a number of pacing protocols are commonly used to quantify the restitution relation, one of these, the dynamic protocol, may result in the occurrence of APD alternans. However, the effects of APD alternans, and the concomitant alternation in cardiac memory, on the restitution curve are currently not well understood. Alternans preceding a given action potential may cause that action potential to have a different duration from one preceded by action potentials of identical duration. This interaction of alternans and memory can result in a dynamic restitution curve that is not unique. To address this, we have developed a constant-memory restitution protocol that enables the experimenter or modeller to obtain unique, constant-memory restitution curves at all diastolic intervals. Using this protocol, we obtained unique restitution curves for two ionic models of the cardiac action potential in the absence of alternans at all diastolic intervals. A comparison of the unique constant-memory and non-unique dynamic restitution curves for the two models shows that the presence of alternans can significantly alter the shape of the restitution curve compared to when alternans is absent.
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Affiliation(s)
- Peter N Jordan
- Department of Physiology and Biophysics, Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA
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Watanabe T, Yamaki M, Yamauchi S, Minamihaba O, Miyashita T, Kubota I, Tomoike H. Regional prolongation of ARI and altered restitution properties cause ventricular arrhythmia in heart failure. Am J Physiol Heart Circ Physiol 2002; 282:H212-8. [PMID: 11748065 DOI: 10.1152/ajpheart.2002.282.1.h212] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mechanism of arrhythmogenicity in heart failure remains poorly understood. We examined the relationship between electrical abnormalities and ventricular arrhythmia by using experimental heart failure models. Sixty unipolar electrograms were recorded from the entire cardiac surface in control dogs (n = 13) and pacing-induced heart failure dogs (n = 16). In failing hearts, activation time (AT) was delayed at the apex, and AT dispersion increased in failing hearts. Activation-recovery intervals (ARI) were prolonged mainly at the apex and ARI dispersion was significantly augmented. The slope of the ARI restitution curve, interaction of diastolic interval, and ARI in failing hearts was significantly steeper than in control hearts. Ventricular fibrillation (VF) was easily induced by programmed stimulation in failing hearts, whereas no arrhythmia occurred in control hearts. Computer simulation studies could reproduce the experimental results. Altering the ARI restitution to the steep slope causes VF in a model heart. It is suggested that electrical remodeling, especially steepness of electrical restitution, may play a role in arrhythmogenicity in failing hearts.
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Affiliation(s)
- Tetsu Watanabe
- First Department of Internal Medicine, Yamagata University School of Medicine, 2-2-2 Iida-Nishi, Yamagata 990-9585, Japan
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Watanabe T, Yamaki M, Tachibana H, Yamauchi S, Kubota I, Tomoike H. Anisotropic effects of sodium channel blockers on the wavelength for ventricular excitation in dogs. JAPANESE CIRCULATION JOURNAL 2000; 64:689-94. [PMID: 10981854 DOI: 10.1253/jcj.64.689] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The purpose of this study was to determine the anisotropic effects of sodium channel blockers on wavelength (WL) and proarrhythmia. In 18 anesthetized, open chest dogs, a 64-electrode array was placed on the left ventricle and the ventricle was constantly paced. Disopyramide, lidocaine or flecainide was intracoronarily administered. Conduction velocity (theta) and activation-recovery interval (ARI) were measured in the longitudinal (L) and transverse (T) directions. Flecainide markedly decreased thetaL, but did not alter thetaT or ARIs in either direction. As a result, the wavelength was significantly shortened only in the L direction. Disopyramide or lidocaine did not show direction-dependent effects on theta or WL. In 3 of 6 dogs with flecainide exposure, ventricular fibrillation (VF) developed. However, no VF occurred with disopyramide or lidocaine. Accordingly, the WL is dependent on the fiber orientation of myocardium. The anisotropic shortening of the WL may explain the character of the proarrhythmia observed with flecainide.
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Affiliation(s)
- T Watanabe
- First Department of Internal Medicine, Yamagata University School of Medicine, Japan.
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Miyashita T, Kubota I, Yamaki M, Watanabe T, Yamauchi S, Tomoike H. 4-aminopyridine inhibits the occurrence of ventricular fibrillation but not ventricular tachycardia in the reperfused, P6olated rat heart. JAPANESE CIRCULATION JOURNAL 2000; 64:602-5. [PMID: 10952157 DOI: 10.1253/jcj.64.602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The 4-aminopyridine (4-AP)-sensitive transient outward current (Ito) has been reported to play an important role in the ischemia- or high [Ca2+]o-induced reentrant ventricular arrhythmias. However, the role of 4-AP sensitive Ito in reperfusion arrhythmia remains unknown. Rat hearts were perfused with Tyrode solution (control), and treated with 0.5 micromol/L verapamil, 1 micromol/L glibenclamide, 10 micromol/L E-4031 or 2 mmol/L 4-AP. After a 10-min perfusion, hearts were subjected to 30-min global ischemia followed by 10-min reperfusion. The effects of the ion-channel blockers on the incidence of ventricular tachycardia (VT), torsades de pointes (Tdp) and ventricular fibrillation (VF) during the reperfusion period were investigated. Verapamil and 4-AP abolished VF and Tdp. The incidence of VT was also attenuated by verapamil, but not by 4-AP. Glibenclamide and E-4031 (a blocker of a rapidly activating component of delayed rectifier K+ current) did not affect the incidence of those tachyarrhythmias. Accordingly, (1) the underlying mechanism of VF or Tdp is different from that of VT, and (2) 4-AP sensitive Ito is required for the occurrence of reperfusion Tdp or VF in the present model.
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Affiliation(s)
- T Miyashita
- First Department of Internal Medicine, Yamagata University School of Medicine, Japan
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