Aim: Low-energy (<100 mJ) line stimulation is a promising approach to terminate ventricular arrhythmias without the inherent risks of strong far-field DC shocks. However, the precise parameters to maximize the capture of the excitable gap during reentrant ventricular arrhythmias are unknown. This study aims to determine the optimal conditions for which low-energy defibrillation is achievable.
Methods: Simulations were performed with the cardiac simulator CARP (Cardiosolv, LLC). An image-based computer model of the human ventricles with ten Tusscher ventricular myocyte membrane kinetics was used for the simulations. Electrode lines were placed 2 cm apart across the surfaces of the ventricles and oriented base to apex. Ventricles were preconditioned with 4 seconds of pacing at 2.5 Hz from a single line located at the LV. Reentrant arrhythmia resembling ventricular fibrillation (VF) was induced with 10 beats at ≥4 Hz from the same line. Defibrillation was attempted through a single low-energy (8x pacing threshold) 2 ms pulse from all lines with varying delay (0.1 to 5 sec) from the end of the VF induction protocol. Arrhythmia complexity was determined by analyzing the dominant frequency and the excitable gap was established as the percentage of tissue with membrane potential <-70 mV.
Results: VF resulted from reentry and increased in complexity from 3.7 to 5 Hz >4sec after VF induction. The excitable gap was reduced from 32% at 0.8 sec post-VF initiation to 3.2% after 3.4 seconds. Low-energy defibrillation was only successful during the early stage of VF when more tissue was accessible and stable for activation.
Conclusions: The optimal conditions for VF defibrillation are within the first second post-VF when arrhythmia complexity is reduced and more excitable gap is available. Future studies should focus on determining the optimal location and shape of the electrodes to maximize the capture of excitable tissue.