• Lukas J Rantner, Brock M Tice, and Natalia A Trayanova.
• Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
• Heart Rhythm. 2013 Aug 1; 10 (8): 1209-17.

BackgroundLow-voltage termination of ventricular tachycardia (VT) and atrial fibrillation has shown promising results; however, the mechanisms and full range of applications remain unexplored.ObjectivesTo elucidate the mechanisms for low-voltage cardioversion and defibrillation and to develop an optimal low-voltage defibrillation protocol.MethodsWe developed a detailed magnetic resonance imaging-based computational model of the rabbit right ventricular wall. We applied multiple low-voltage far-field stimuli of various strengths (≤1 V/cm) and stimulation rates in VT and ventricular fibrillation (VF).ResultsOf the 5 stimulation rates tested, stimuli applied at 16% or 88% of the VT cycle length (CL) were most effective in cardioverting VT, the mechanism being consecutive excitable gap decreases. Stimuli given at 88% of the VF CL defibrillated successfully, whereas a faster stimulation rate (16%) often failed because the fast stimuli did not capture enough tissue. In this model, defibrillation threshold energy for multiple low-voltage stimuli at 88% of VF CL was 0.58% of the defibrillation threshold energy for a single strong biphasic shock. Based on the simulation results, a novel 2-stage defibrillation protocol was proposed. The first stage converted VF into VT by applying low-voltage stimuli at times of maximal excitable gap, capturing large tissue volume and synchronizing depolarization; the second stage terminated VT. The energy required for successful defibrillation using this protocol was 57.42% of the energy for low-voltage defibrillation when stimulating at 88% of VF CL.ConclusionsA novel 2-stage low-voltage defibrillation protocol using the excitable gap extent to time multiple stimuli defibrillated VF with the least energy by first converting VF into VT and then terminating VT.Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

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