Determining Surface Stimulation Parameters With Computational Cardiac Electrophysiology to Defibrillate Human Ventricles

Abstract

Aim: To determine the minimal surface stimulus strength necessary to defibrillate human ventricles. Methods: We determined this in a 10cmx10cmx1cm finite element model of left ventricular (LV) tissue with human electrophysiology. It was paced until steady-state at 1.3 Hz with S1 stimuli (LV apex) at 2x threshold. A single S2 stimulus (apical posterior corner) was delivered at 2x threshold 300 ms after the last S1 to initiate reentry at the model's center. To terminate reentry, an S3 stimulus on the entire epicardial, endocardial, or both surfaces was applied 2 seconds after S2. Starting at the capture threshold, S3 strength was doubled until reentry terminated. Results: Minimum stimulus strength to terminate reentry with endocardial and epicardial S3 was > 512-fold capture threshold, but only 16-fold for S3 applied to both surfaces simultaneously. Extending the S3 depth to the midmyocardium lowered the minimum stimulus strength for defibrillation to 8-fold capture threshold on the endocardium and 16-fold on the epicardium. This difference corresponds to a longer wavelength for reentry in the endocardium versus epicardium (6.6 cm vs 5.3 cm). Conclusion: Stimulating both the endocardial and epicardial surfaces at $\ge 16$ times capture threshold is optimal to defibrillate human ventricles, and is decreased further for stimuli applied deeper in the tissue.