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Mazumder O, Banerjee R, Roy D, Mukherjee A, Ghose A, Khandelwal S, Sinha A. Computational Model for Therapy Optimization of Wearable Cardioverter Defibrillator: Shockable Rhythm Detection and Optimal Electrotherapy. Front Physiol 2021; 12:787180. [PMID: 34955894 PMCID: PMC8703044 DOI: 10.3389/fphys.2021.787180] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 11/08/2021] [Indexed: 11/15/2022] Open
Abstract
Wearable cardioverter defibrillator (WCD) is a life saving, wearable, noninvasive therapeutic device that prevents fatal ventricular arrhythmic propagation that leads to sudden cardiac death (SCD). WCD are frequently prescribed to patients deemed to be at high arrhythmic risk but the underlying pathology is potentially reversible or to those who are awaiting an implantable cardioverter-defibrillator. WCD is programmed to detect appropriate arrhythmic events and generate high energy shock capable of depolarizing the myocardium and thus re-initiating the sinus rhythm. WCD guidelines dictate very high reliability and accuracy to deliver timely and optimal therapy. Computational model-based process validation can verify device performance and benchmark the device setting to suit personalized requirements. In this article, we present a computational pipeline for WCD validation, both in terms of shock classification and shock optimization. For classification, we propose a convolutional neural network-"Long Short Term Memory network (LSTM) full form" (Convolutional neural network- Long short term memory network (CNN-LSTM)) based deep neural architecture for classifying shockable rhythms like Ventricular Fibrillation (VF), Ventricular Tachycardia (VT) vs. other kinds of non-shockable rhythms. The proposed architecture has been evaluated on two open access ECG databases and the classification accuracy achieved is in adherence to American Heart Association standards for WCD. The computational model developed to study optimal electrotherapy response is an in-silico cardiac model integrating cardiac hemodynamics functionality and a 3D volume conductor model encompassing biophysical simulation to compute the effect of shock voltage on myocardial potential distribution. Defibrillation efficacy is simulated for different shocking electrode configurations to assess the best defibrillator outcome with minimal myocardial damage. While the biophysical simulation provides the field distribution through Finite Element Modeling during defibrillation, the hemodynamic module captures the changes in left ventricle functionality during an arrhythmic event. The developed computational model, apart from acting as a device validation test-bed, can also be used for the design and development of personalized WCD vests depending on subject-specific anatomy and pathology.
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Clementy N, Bodin A, Bisson A, Teixeira-Gomes AP, Roger S, Angoulvant D, Labas V, Babuty D. The Defibrillation Conundrum: New Insights into the Mechanisms of Shock-Related Myocardial Injury Sustained from a Life-Saving Therapy. Int J Mol Sci 2021; 22:ijms22095003. [PMID: 34066832 PMCID: PMC8125879 DOI: 10.3390/ijms22095003] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 05/03/2021] [Accepted: 05/05/2021] [Indexed: 11/16/2022] Open
Abstract
Implantable cardiac defibrillators (ICDs) are recommended to prevent the risk of sudden cardiac death. However, shocks are associated with an increased mortality with a dose response effect, and a strategy of reducing electrical therapy burden improves the prognosis of implanted patients. We review the mechanisms of defibrillation and its consequences, including cell damage, metabolic remodeling, calcium metabolism anomalies, and inflammatory and pro-fibrotic remodeling. Electrical shocks do save lives, but also promote myocardial stunning, heart failure, and pro-arrhythmic effects as seen in electrical storms. Limiting unnecessary implantations and therapies and proposing new methods of defibrillation in the future are recommended.
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Affiliation(s)
- Nicolas Clementy
- Service de Cardiologie, Hôpital Trousseau, Université de Tours, 37044 Tours, France; (A.B.); (A.B.); (D.A.); (D.B.)
- Transplantation, Immunologie et Inflammation T2I-EA 4245, Université de Tours, 37044 Tours, France;
- Correspondence: ; Tel.: +33-247-474-687; Fax: +33-247-475-919
| | - Alexandre Bodin
- Service de Cardiologie, Hôpital Trousseau, Université de Tours, 37044 Tours, France; (A.B.); (A.B.); (D.A.); (D.B.)
| | - Arnaud Bisson
- Service de Cardiologie, Hôpital Trousseau, Université de Tours, 37044 Tours, France; (A.B.); (A.B.); (D.A.); (D.B.)
- Transplantation, Immunologie et Inflammation T2I-EA 4245, Université de Tours, 37044 Tours, France;
| | - Ana-Paula Teixeira-Gomes
- Plate-forme de Chirurgie et d’Imagerie pour la Recherche et l’Enseignement (CIRE), INRA, Université de Tours, CHU de Tours, 37380 Nouzilly, France; (A.-P.T.-G.); (V.L.)
| | - Sebastien Roger
- Transplantation, Immunologie et Inflammation T2I-EA 4245, Université de Tours, 37044 Tours, France;
| | - Denis Angoulvant
- Service de Cardiologie, Hôpital Trousseau, Université de Tours, 37044 Tours, France; (A.B.); (A.B.); (D.A.); (D.B.)
- Transplantation, Immunologie et Inflammation T2I-EA 4245, Université de Tours, 37044 Tours, France;
| | - Valérie Labas
- Plate-forme de Chirurgie et d’Imagerie pour la Recherche et l’Enseignement (CIRE), INRA, Université de Tours, CHU de Tours, 37380 Nouzilly, France; (A.-P.T.-G.); (V.L.)
| | - Dominique Babuty
- Service de Cardiologie, Hôpital Trousseau, Université de Tours, 37044 Tours, France; (A.B.); (A.B.); (D.A.); (D.B.)
- Transplantation, Immunologie et Inflammation T2I-EA 4245, Université de Tours, 37044 Tours, France;
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Joshi J, Rubart M, Zhu W. Optogenetics: Background, Methodological Advances and Potential Applications for Cardiovascular Research and Medicine. Front Bioeng Biotechnol 2020; 7:466. [PMID: 32064254 PMCID: PMC7000355 DOI: 10.3389/fbioe.2019.00466] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/19/2019] [Indexed: 12/27/2022] Open
Abstract
Optogenetics is an elegant approach of precisely controlling and monitoring the biological functions of a cell, group of cells, tissues, or organs with high temporal and spatial resolution by using optical system and genetic engineering technologies. The field evolved with the need to precisely control neurons and decipher neural circuity and has made great accomplishments in neuroscience. It also evolved in cardiovascular research almost a decade ago and has made considerable progress in both in vitro and in vivo animal studies. Thus, this review is written with an objective to provide information on the evolution, background, methodical advances, and potential scope of the field for cardiovascular research and medicine. We begin with a review of literatures on optogenetic proteins related to their origin, structure, types, mechanism of action, methods to improve their performance, and the delivery vehicles and methods to express such proteins on target cells and tissues for cardiovascular research. Next, we reviewed historical and recent literatures to demonstrate the scope of optogenetics for cardiovascular research and regenerative medicine and examined that cardiac optogenetics is vital in mimicking heart diseases, understanding the mechanisms of disease progression and also in introducing novel therapies to treat cardiac abnormalities, such as arrhythmias. We also reviewed optogenetics as promising tools in providing high-throughput data for cardiotoxicity screening in drug development and also in deciphering dynamic roles of signaling moieties in cell signaling. Finally, we put forth considerations on the need of scaling up of the optogenetic system, clinically relevant in vivo and in silico models, light attenuation issues, and concerns over the level, immune reactions, toxicity, and ectopic expression with opsin expression. Detailed investigations on such considerations would accelerate the translation of cardiac optogenetics from present in vitro and in vivo animal studies to clinical therapies.
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Affiliation(s)
- Jyotsna Joshi
- Department of Cardiovascular Medicine, Physiology and Biomedical Engineering, Mayo Clinic, Phoenix, AZ, United States
| | - Michael Rubart
- Department of Pediatrics, Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, United States
| | - Wuqiang Zhu
- Department of Cardiovascular Medicine, Physiology and Biomedical Engineering, Mayo Clinic, Phoenix, AZ, United States
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Osadchii OE. Determinants of slowed conduction in premature ventricular beats induced during programmed stimulations in perfused guinea-pig heart. Exp Physiol 2018; 103:1230-1242. [PMID: 29956404 DOI: 10.1113/ep087019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 06/27/2018] [Indexed: 12/26/2022]
Abstract
NEW FINDINGS What is the central question of this study? Is the slowed conduction upon premature ventricular activations during clinical electrophysiological testing attributable to the prolonged activation latency, or increased impulse propagation time, or both? What is the main finding and its importance? Prolonged activation latency at the stimulation site is the critical determinant of conduction slowing and associated changes in the ventricular response intervals in premature beats initiated during phase 3 repolarization in perfused guinea-pig heart. These relations are likely to have an effect on arrhythmia induction and termination independently of the presence of ventricular conduction defects or the proximity of the stimulation site to the re-entrant circuit. ABSTRACT During cardiac electrophysiological testing, slowed conduction upon premature ventricular activation can limit the delivery of the closely coupled impulses from the stimulation site to the region of tachycardia origin. In order to examine the contributing factors, in this study, cardiac conduction intervals and refractory periods were determined from left ventricular (LV) and the right ventricular (RV) monophasic action potential recordings obtained in perfused guinea-pig hearts. A premature activation induced immediately after the termination of the refractory period was associated with conduction slowing. The latter was primarily accounted for by the markedly increased (+54%) activation latency at the LV stimulation site, with only negligible changes (+12%) noted in the LV-to-RV delay. The prolonged activation latency was acting to limit the shortest interval at which two successive action potentials can be induced in the LV and RV chambers. The prolongation of the activation latency in premature beats was accentuated upon an increase in the stimulating current intensity, or during hypokalaemia. This change was related to the reduced ratio of the refractory period to the action potential duration, which allowed extrastimulus capture to occur earlier during phase 3 repolarization. Flecainide, a Na+ channel blocker, prolonged both the activation latency and the LV-to-RV delay, without changing their relative contributions to conduction slowing. In summary, these findings suggest that the activation latency is the critical determinant of conduction slowing and associated changes in the ventricular response intervals upon extrastimulus application during phase 3 of the action potential.
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Affiliation(s)
- Oleg E Osadchii
- Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen N, Denmark.,Department of Health Science and Technology, University of Aalborg, Fredrik Bajers Vej 7E, Aalborg, Denmark
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Karagueuzian HS, Pezhouman A, Angelini M, Olcese R. Enhanced Late Na and Ca Currents as Effective Antiarrhythmic Drug Targets. Front Pharmacol 2017; 8:36. [PMID: 28220073 PMCID: PMC5292429 DOI: 10.3389/fphar.2017.00036] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 01/18/2017] [Indexed: 11/30/2022] Open
Abstract
While recent advances clarified the molecular and cellular modes of action of antiarrhythmic drugs (AADs), their link to suppression of dynamical arrhythmia mechanisms remains only partially understood. The current classifications of AADs (Classes I, III, and IV) rely on blocking peak Na, K and L-type calcium currents (ICa,L), with Class II with dominant beta receptor blocking activity and Class V including drugs with diverse classes of actions. The discovery that the calcium and redox sensor, cardiac Ca/calmodulin-dependent protein kinase II (CaMKII) enhances both the late Na (INa-L) and the late ICa,L in patients at high risk of VT/VF provided a new and a rational AAD target. Pathological rise of either or both of INa-L and late ICa,L are demonstrated to promote cellular early afterdepolarizations (EADs) and EAD-mediated triggered activity that can initiate VT/VF in remodeled hearts. Selective inhibition of the INa-L without affecting their peak transients with the highly specific prototype drug, GS-967 suppresses these EAD-mediated VT/VFs. As in the case of INa-L, selective inhibition of the late ICa,L without affecting its peak with the prototype drug, roscovitine suppressed oxidative EAD-mediated VT/VF. These findings indicate that specific blockers of the late inward currents without affecting their peaks (gating modifiers), offer a new and effective AAD class action i.e., “Class VI.” The development of safe drugs with selective Class VI actions provides a rational and effective approach to treat VT/VF particularly in cardiac conditions associated with enhanced CaMKII activity such as heart failure.
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Affiliation(s)
- Hrayr S Karagueuzian
- Translational Arrhythmia Section, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
| | - Arash Pezhouman
- Translational Arrhythmia Section, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
| | - Marina Angelini
- Department of Anesthesiology and Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA
| | - Riccardo Olcese
- Cardiovascular Research Laboratory, Departments of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Department of Anesthesiology and Perioperative Medicine, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA; Department of Physiology, David Geffen School of Medicine, University of California, Los AngelesLos Angeles, CA, USA
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Optogenetics design of mechanistically-based stimulation patterns for cardiac defibrillation. Sci Rep 2016; 6:35628. [PMID: 27748433 PMCID: PMC5066272 DOI: 10.1038/srep35628] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Accepted: 10/04/2016] [Indexed: 12/31/2022] Open
Abstract
Current rescue therapies for life-threatening arrhythmias ignore the pathological electro-anatomical substrate and base their efficacy on a generalized electrical discharge. Here, we developed an all-optical platform to examine less invasive defibrillation strategies. An ultrafast wide-field macroscope was developed to optically map action potential propagation with a red-shifted voltage sensitive dye in whole mouse hearts. The macroscope was implemented with a random-access scanning head capable of drawing arbitrarily-chosen stimulation patterns with sub-millisecond temporal resolution allowing precise epicardial activation of Channelrhodopsin2 (ChR2). We employed this optical system in the setting of ventricular tachycardia to optimize mechanistic, multi-barrier cardioversion/defibrillation patterns. Multiple regions of conduction block were created with a very high cardioversion efficiency but with lower energy requirements as compared to whole ventricle interventions to interrupt arrhythmias. This work demonstrates that defibrillation energies can be substantially reduced by applying discrete stimulation patterns and promotes the progress of current anti-arrhythmic strategies.
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Lawo T, Deneke T, Schrader J, Danilovic D, Wenzel B, Buddensiek M, Muegge A. A comparison of chronaxies for ventricular fibrillation induction, defibrillation, and cardiac stimulation: unexpected findings and their implications. J Cardiovasc Electrophysiol 2008; 20:307-14. [PMID: 19175850 DOI: 10.1111/j.1540-8167.2008.01319.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
INTRODUCTION A low-energy (<or= 4 J) cardioversion shock (LEC) either terminates reentrant ventricular tachycardia (VT) or accelerates it to ventricular fibrillation (VF). Optimization of the duration and amplitude of LEC shocks could improve the success rate of VT termination without VF induction. METHODS AND RESULTS In order to learn how LEC shocks may be optimized, we used an animal model to compare the strength-duration curve for VF induction and the strength-duration curve for cardiac stimulation via the shock coil. Conventional implantable cardioverter-defibrillator (ICD) leads were implanted in 12 narcotized pigs from 20 kg to 25 kg in weight. Stimulation, VF induction, and defibrillation pulses were delivered by custom-designed stimulators at preset pulse durations and amplitudes. The corresponding hyperbolic strength-duration curves were constructed using the least-squares fit method and averaged for all the animals. The mean chronaxie for stimulation via the shock coil of 0.23 ms was significantly shorter than both defibrillation (4.8 ms) and VF induction (3.1 ms) chronaxie values. At a shock duration of 0.3 ms or less, the mean VF-induction threshold amplitude exceeded 300 V. CONCLUSION It may be reasonable to study whether LEC pulses from 0.25 ms to 0.30 ms in duration and up to 250 V in amplitude would increase therapeutic yield in VT termination without VF induction in humans. Contrary to the current belief, the discrepancy between defibrillation and stimulation chronaxie is not caused by different electrode size. We postulate that the time constant of the fast sodium channel reactivation may be the underlying reason.
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Affiliation(s)
- Thomas Lawo
- Medical Clinic II (Cardiology), BG University Hospital Bergmannsheil, Bochum, Germany.
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Imaging fibrillation/defibrillation in a dish. J Electrocardiol 2007; 40:S62-5. [DOI: 10.1016/j.jelectrocard.2007.06.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Accepted: 06/05/2007] [Indexed: 11/21/2022]
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Yang MJ, Tran DX, Weiss JN, Garfinkel A, Qu Z. The pinwheel experiment revisited: effects of cellular electrophysiological properties on vulnerability to cardiac reentry. Am J Physiol Heart Circ Physiol 2007; 293:H1781-90. [PMID: 17586622 DOI: 10.1152/ajpheart.00014.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In normal heart, ventricular fibrillation can be induced by a single properly timed strong electrical or mechanical stimulus. A mechanism first proposed by Winfree and coined the “pinwheel experiment” emphasizes the timing and strength of the stimulus in inducing figure-of-eight reentry. However, the effects of cellular electrophysiological properties on vulnerability to reentry in the pinwheel scenario have not been investigated. In this study, we extend Winfree's pinwheel experiment to show how the vulnerability to reentry is affected by the graded action potential responses induced by a strong premature stimulus, action potential duration (APD), and APD restitution in simulated monodomain homogeneous two-dimensional tissue. We find that a larger graded response, longer APD, or steeper APD restitution slope reduces the vulnerable window of reentry. Strong graded responses and long APD promote tip-tip interactions at long coupling intervals, causing the two initiated spiral wave tips to annihilate. Steep APD restitution promotes wave front-wave back interaction, causing conduction block in the central common pathway of figure-of-eight reentry. We derive an analytical treatment that shows good agreement with numerical simulation results.
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Affiliation(s)
- Ming-Jim Yang
- Cardiovascular Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles 90095, USA
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Karagueuzian HS. “Conduction Gate” and Ventricular Graded Responses. Heart Rhythm 2007; 4:989; author reply 989-90. [PMID: 17599692 PMCID: PMC1948847 DOI: 10.1016/j.hrthm.2007.03.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Indexed: 10/23/2022]
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Spach MS, Barr RC. To the Editor—Response. Heart Rhythm 2007. [DOI: 10.1016/j.hrthm.2007.03.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Spach MS, Heidlage JF, Dolber PC, Barr RC. Mechanism of origin of conduction disturbances in aging human atrial bundles: experimental and model study. Heart Rhythm 2006; 4:175-85. [PMID: 17275753 PMCID: PMC1847326 DOI: 10.1016/j.hrthm.2006.10.023] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Accepted: 10/24/2006] [Indexed: 11/16/2022]
Abstract
BACKGROUND Aging is associated with a significant increase in atrial tachyarrhythmias, especially atrial fibrillation. A macroscopic repolarization gradient created artificially by a stimulus at one site before a premature stimulus from a second site is widely considered to be part of the experimental protocol necessary for the initiation of such arrhythmias in the laboratory. How such gradients occur naturally in aging atrial tissue is unknown. OBJECTIVE The objective of this study was to determine if the pattern of cellular connectivity in aging human atrial bundles produces a mechanism for variable early premature responses. METHODS Extracellular and intracellular potentials were recorded after control and premature stimuli at a single site in aging human atrial bundles. We also measured cellular geometry, the distribution of connexins, and the distribution of collagenous septa. A model of the atrial bundles was constructed based on the morphological results. Action potential propagation and the sodium current were analyzed after premature stimuli in the model. RESULTS Similar extracellular potential waveform responses occurred after early premature stimuli in the aging bundles and in the model. Variable premature conduction patterns were accounted for by the single model of aging atrial structure. A major feature of the model results was that the conduction events and the magnitude of the sodium current at multiple sites were very sensitive to small changes in the location and the timing of premature stimuli. CONCLUSION In aging human atrial bundles stimulated from only a single site, premature stimuli induce variable arrhythmogenic conduction responses. The generation of these responses is greatly enhanced by remodeling of cellular connectivity during aging. The results provide insight into sodium current structural interactions as a general mechanism of arrhythmogenic atrial responses to premature stimuli.
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Affiliation(s)
- Madison S Spach
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Sharifov OF, Fast VG. Role of intramural virtual electrodes in shock-induced activation of left ventricle: Optical measurements from the intact epicardial surface. Heart Rhythm 2006; 3:1063-73. [PMID: 16945803 DOI: 10.1016/j.hrthm.2006.05.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Accepted: 05/12/2006] [Indexed: 10/24/2022]
Abstract
BACKGROUND According to one hypothesized mechanism of defibrillation, shocks directly excite the bulk of ventricular myocardium in the excitable state due to intramural virtual electrodes; however, this hypothesis has not been examined in intact myocardium. OBJECTIVES The purpose of this study was examine the role of intramural virtual electrodes in shock-induced activation of intact left ventricular (LV) tissue. METHODS Twelve isolated porcine LV preparations were stained with a transmembrane potential (V(m))-sensitive dye by two methods: (1) surface staining and (2) global staining via coronary perfusion. Shocks (E approximately 0.8-48 V/cm, duration = 10 ms) were applied across the wall from epicardium to endocardium during diastole via transparent electrodes. Shock-induced V(m) responses were measured optically from the intact epicardial surface after surface staining and global staining. RESULTS Surface-staining recordings demonstrated different V(m) responses to cathodal and anodal shocks. Whereas cathodal shocks caused depolarization and rapid activation of the epicardial surface, anodal shocks induced hyperpolarization and delayed surface activation. In contrast, global-staining V(m) responses to cathodal and anodal shocks were qualitatively similar. Both responses were characterized by activation with small latency and rapid propagation. Weak shocks of both polarities induced monotonic action potential upstrokes; stronger shocks induced nonmonotonic upstrokes with two rising phases at shock onset and end. Such features of global-staining V(m) responses as make activation of the epicardium by anodal shocks and the nonmonotonic action potential upstrokes can be explained by the presence of subepicardial intramural virtual electrodes. CONCLUSION These data suggest that shocks induce intramural virtual electrodes that directly excite LV tissue and account for the shape of optical V(m) responses recorded from the epicardial surface.
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Affiliation(s)
- Oleg F Sharifov
- Department of Biomedical Engineering, University of Alabama at Birmingham, 35294, USA
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Beaudoin DL, Roth BJ. The effect of the fiber curvature gradient on break excitation in cardiac tissue. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2006; 29:496-501. [PMID: 16689845 DOI: 10.1111/j.1540-8159.2006.00382.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Break excitation has been hypothesized as a mechanism for the initiation of reentry in cardiac tissue. One way break excitation can occur is by virtual electrodes formed due to a curving fiber geometry. In this article, we are concerned with the relationship between the peak gradient of fiber curvature and the threshold for break stimulation and the initiation of reentry. METHODS We calculate the maximum gradient of fiber curvature for different scales of fiber geometry in a constant tissue size (20x20 mm), and also examine the mechanisms by which reentry initiation fails. RESULTS For small peak gradients, reentry fails because break excitation does not occur. For larger peak gradients, reentry fails because break excitation fails to develop into full-scale reentry. For strong stimuli above the upper limit of vulnerability, reentry fails because the break excitation propagates through the hyperpolarized region and then encounters refractory tissue, causing the wave front to die.
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Bourn DW, Gray RA, Trayanova NA. Characterization of the relationship between preshock state and virtual electrode polarization-induced propagated graded responses resulting in arrhythmia induction. Heart Rhythm 2006; 3:583-95. [PMID: 16648066 DOI: 10.1016/j.hrthm.2006.01.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Accepted: 01/22/2006] [Indexed: 11/21/2022]
Abstract
BACKGROUND Studies have demonstrated that failed defibrillation shocks often are followed by an electrically quiescent period (isoelectric window); however, the underlying mechanisms remain incompletely understood. We recently suggested a new mechanism termed "virtual electrode polarization-induced propagated graded responses" (VEPiPGRs) that might play a role in the origin of the global postshock activation following the isoelectric window. OBJECTIVES The purpose of this study to elucidate the circumstances under which VEPiPGR activations originate for shocks given to paced right ventricular preparations. Specifically, we examined the dependence of VEPiPGRs on coupling interval (CI) and shock polarity and whether VEPiPGRs emerge preferentially on the epicardium or the endocardium. METHODS Simultaneous endocardial and epicardial activity in isolated right ventricular preparations (n = 4) was imaged optically following shocks of strength +/-5A. All VEPiPGRs were analyzed, and the time T from shock end to activation onset was recorded (isoelectric window is the smallest T among activations that propagated globally). RESULTS VEPiPGR activations occurred for CIs in the range from 80 to 150 ms. Average duration of T was 64.5 +/- 18.15 ms, with T decreasing as CI increased (Tmax = 82 ms, Tmin = 46 ms, linear-fit slope = -0.675). The average earliest CI at which cathodal (+5A) shocks resulted in VEPiPGRs was 87 ms compared with 116 ms for anodal (-5A) shocks. All VEPiPGR activations emerged first on the epicardium in a focal pattern, and all induced ventricular fibrillation. CONCLUSION The global activation that terminates the isoelectric window could result from VEPiPGRs that find an exit pathway. VEPiPGRs originate at the sites of maximum action potential abbreviation by the shock, always on the epicardium for the preparation used here.
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Affiliation(s)
- David W Bourn
- Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118, USA
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Laudi S, Vu Tran Z, Steudel W. Cariporide in cardiac resuscitation—Does it really make a difference?*. Crit Care Med 2005; 33:2707-8. [PMID: 16276214 DOI: 10.1097/01.ccm.0000186885.52950.79] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Gelzer AR, Moïse NS, Koller ML. Defibrillation of German shepherds with inherited ventricular arrhythmias and sudden death. J Vet Cardiol 2005; 7:97-107. [DOI: 10.1016/j.jvc.2005.09.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 09/23/2005] [Accepted: 09/25/2005] [Indexed: 10/25/2022]
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Hillebrenner MG, Eason JC, Trayanova NA. Mechanistic inquiry into decrease in probability of defibrillation success with increase in complexity of preshock reentrant activity. Am J Physiol Heart Circ Physiol 2003; 286:H909-17. [PMID: 14604852 DOI: 10.1152/ajpheart.00492.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Energy requirements for successful antiarrhythmia shocks are arrhythmia specific. However, it remains unclear why the probability of shock success decreases with increasing arrhythmia complexity. The goal of this research was to determine whether a diminished probability of shock success results from an increased number of functional reentrant circuits in the myocardium, and if so, to identify the responsible mechanisms. To achieve this goal, we assessed shock efficacy in a bidomain defibrillation model of a 4-mm-thick slice of canine ventricles. Shocks were applied between a right ventricular cathode and a distant anode to terminate either a single scroll wave (SSW) or multiple scroll waves (MSWs). From the 160 simulations conducted, dose-response curves were constructed for shocks given to SSWs and MSWs. The shock strength that yielded a 50% probability of success (ED(50)) for SSWs was found to be 13% less than that for MSWs, which indicates that a larger number of functional reentries results in an increased defibrillation threshold. The results also demonstrate that an isoelectric window exists after both failed and successful shocks; however, shocks of strength near the ED(50) value that were given to SSWs resulted in 16.3% longer isoelectric window durations than the same shocks delivered to MSWs. Mechanistic inquiry into these findings reveals that the two main factors underlying the observed relationships are 1) smaller virtual electrode polarizations in the tissue depth, and 2) differences in preshock tissue state. As a result of these factors, intramural excitable pathways leading to delayed breakthrough on the surface were formed earlier after shocks given to MSWs compared with SSWs and thus resulted in a lower defibrillation threshold for shocks given to SSWs.
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Affiliation(s)
- Matthew G Hillebrenner
- Dept. of Biomedical Engineering, 500 Lindy Boggs Center, Suite 500, Tulane Univ., New Orleans, LA 70118, USA
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Trayanova NA, Gray RA, Bourn DW, Eason JC. Virtual electrode-induced positive and negative graded responses: new insights into fibrillation induction and defibrillation. J Cardiovasc Electrophysiol 2003; 14:756-63. [PMID: 12930258 DOI: 10.1046/j.1540-8167.2003.03042.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Natalia A Trayanova
- Department of Biomedical Engineering, Tulane University, Boggs Center, Suite 500, New Orleans, LA 70118, USA.
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Sims JJ, Miller AW, Ujhelyi MR. Electrical heterogeneity and arrhythmogenesis: importance of conduction velocity dispersion. J Cardiovasc Pharmacol 2003; 41:795-803. [PMID: 12717112 DOI: 10.1097/00005344-200305000-00018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
An experimental model of conduction velocity (CV) and refractory period dispersion was established to determine which variable is a determinant of myocardial vulnerability. Anesthetized swine were instrumented with a left anterior descending coronary artery catheter for regional infusion of lidocaine (n = 6), low-dose d-sotalol (n = 4), high-dose d-sotalol (n = 6), or saline (n = 6), to create dispersion in CV (lidocaine), refractoriness (d-sotalol), or neither (saline). Ventricular fibrillation thresholds (VFTs) and refractory periods were determined at five sites (one drug perfused, four non-drug perfused). CV was determined in one drug-perfused area (left ventricular epicardial apex) and one non-drug perfused area (right ventricular epicardial base). Lidocaine and low- and high-dose d-sotalol increased VFT when stimuli were delivered in the drug-perfused area. However, lidocaine decreased VFT when stimuli were delivered at non-drug perfused areas by an average of 52%. Neither d-sotalol dose affected VFT when stimuli were delivered in non-drug perfused areas. Lidocaine increased CV dispersion by 18-26 cm/s but did not alter refractoriness. Both d-sotalol doses increased dispersion in refractoriness by 15-27 ms but did not alter CV. Saline did not affect either variable. Regional lidocaine had profibrillatory effects when stimuli were delivered in non-drug perfused areas, whereas regional d-sotalol did not. Hence, CV dispersion is a more likely determinant of myocardial vulnerability than refractoriness.
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Affiliation(s)
- J Jason Sims
- University of Georgia College of Pharmacy, Medical College of Georgia, Augusta, USA.
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Kirchhof P, Milberg P, Eckardt L, Breithardt G, Haverkamp W. Effect of sotalol and acute ventricular dilatation on action potential duration and dispersion of repolarization after defibrillation shocks. J Cardiovasc Pharmacol 2003; 41:640-8. [PMID: 12658067 DOI: 10.1097/00005344-200304000-00018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Ventricular dilatation shortens action potential duration and increases the defibrillation threshold, whereas sotalol prolongs action potential duration and may decrease the defibrillation threshold. Whether these action potential changes remain after defibrillation shocks, and how they relate to defibrillation success, is not known. In this study, eight monophasic action potentials were recorded simultaneously during electrical defibrillation (shock strength: 20%-200% of the defibrillation threshold) in 16 normal and acutely dilated isolated rabbit hearts at baseline and after addition of sotalol (2 x 10-5 M). Post-shock action potential duration (PS-APD) and dispersion of PS-APD [Disp(PS-APD)] of monophasic action potentials were analyzed after 322 defibrillation shocks at different repolarization levels and related to defibrillation success. Acute ventricular dilatation shortened PS-APD, whereas sotalol prolonged PS-APD. Successful defibrillation was associated with lower Disp(PS-APD) at all repolarization levels in the normal and dilated heart at baseline and with sotalol (mean difference: 33%-46%, all P < 0.005). Minimal PS-APD was longer (mean difference: 5%-11%), while maximal PS-APD was shorter (mean difference: 2%-16%) after successful defibrillation shocks than after failing defibrillation shocks. Therefore, sotalol prolongs action potential duration after defibrillation shocks. Synchronization of repolarization, caused by both prolongation of short PS-APD and shortening of long PS-APD, is associated with successful defibrillation in the normal, acutely dilated, and sotalol-treated heart.
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Affiliation(s)
- Paulus Kirchhof
- Department of Cardiology and Angiology, University Hospital Münster, Germany.
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Abstract
The transition of biphasic waveforms from ICDs to external defibrillators constitutes a significant technological advances for transthoracic defibrillation. Impedance compensation has enabled the delivery of defibrillating current adapted to each patient and each shock in the same patient. Optimally designed biphasic waveforms have been shown clinically to have greater efficacy in the termination of VF when compared with monophasic waveforms, and because peak current delivery is less, these waveforms are likely to be less injurious to myocardial function. Advances in the understanding of the mechanisms of fibrillation and defibrillation have identified the electrophysiologic events that initiate and sustain VF and the effects of defibrillation shocks on those events. Definition of the role of VEP and postshock excitation has clarified the mechanisms by which shocks can either fail or succeed. The ability of the second phase of optimal biphasic waveform shocks to exploit recruited sodium channels in negatively polarized areas and thus induce rapid propagation of postshock excitation assures uniform depolarization and prevention of re-entry. This appears to be the major mechanism of greater efficacy of biphasic waveforms. It seems certain that continuing investigation of virtual electrodes will enhance our understanding of defibrillation and optimal waveforms. At the same time, much more needs to be known regarding translation of these experimental observations to mechanisms of defibrillation in human hearts with long-standing underlying structural heart disease, which often arises of multiple factors. This represents a major challenge in defibrillation research.
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Affiliation(s)
- Roger D White
- City of Rochester Early Defibrillation Program, Mayo Medical School, 200 First Street SW, Rochester, MN 55905, USA.
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Zou R, Kneller J, Leon LJ, Nattel S. Development of a computer algorithm for the detection of phase singularities and initial application to analyze simulations of atrial fibrillation. CHAOS (WOODBURY, N.Y.) 2002; 12:764-778. [PMID: 12779605 DOI: 10.1063/1.1497505] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Atrial fibrillation (AF) is a common cardiac arrhythmia, but its mechanisms are incompletely understood. The identification of phase singularities (PSs) has been used to define spiral waves involved in maintaining the arrhythmia, as well as daughter wavelets. In the past, PSs have often been identified manually. Automated PS detection algorithms have been described previously, but when we attempted to apply a previously developed algorithm we experienced problems with false positives that made the results difficult to use directly. We therefore developed a tool for PS identification that uses multiple strategies incorporating both image analysis and mathematical convolution for automated detection with optimized sensitivity and specificity, followed by manual verification. The tool was then applied to analyze PS behavior in simulations of AF maintained in the presence of spatially distributed acetylcholine effects in cell grids of varying size. These analyses indicated that in almost all cases, a single PS lasted throughout the simulation, corresponding to the central-core tip of a single spiral wave that maintained AF. The sustained PS always localized to an area of low acetylcholine concentration. When the grid became very small and no area of low acetylcholine concentration was surrounded by zones of higher concentration, AF could not be sustained. The behavior of PSs and the mechanisms of AF were qualitatively constant over an 11.1-fold range of atrial grid size, suggesting that the classical emphasis on tissue size as a primary determinant of fibrillatory behavior may be overstated. (c) 2002 American Institute of Physics.
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Affiliation(s)
- Renqiang Zou
- Research Center and Department of Medicine, Montreal Heart Institute and University of Montreal, Montreal, Quebec, Canada
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