New Approach to Biphasic Waveforms for Internal Defibrillation:

Internal Defibrillation with Fully Discharging Capacitors. Introduction : The use of two independent, fully discharging capacitors for each phase of a biphasic defibrillation waveform may lead to the design of a simpler, smaller, internal defibrillator. The goal of this study was to determine the optimal combination of capacitor sizes for such a waveform. Methods and Results: Eight full‐discharge (95/95% tilt), biphasic waveforms produced by several combinations of phase‐1 capacitors (30, 60, and 90 μF) and phase‐2 capacitors (1/3, 2/3, and 1.0 times the phase‐1 capacitor) were tested and compared to a single‐capacitor waveform (120 μF, 65/65% tilt) in a pig ventricular fibrillation model (n = 12, 23 ± 2 kg). In the full‐discharge waveforms, phase‐2 peak voltage was equal to phase‐1 peak voltage. Shocks were delivered between a right ventricular lead and a left pectoral can electrode. E50s and V50s were determined using a ten‐step Bayesian process. Full‐discharge waveforms with phase‐2 capacitors of ≥40 μF had the same E50 (6.7 ± 1.7 J to 7.3 ± 3.9 J) as the single‐capacitor truncated waveform (7.3 ± 3.7 J), whereas waveforms with phase‐2 capacitors of ≥60 μF had an extremely high E50 (14.5 ± 10.8 J or greater, P < 0.05). Moreover, of the former set of energy‐efficient waveforms, those with phase‐1 capacitors of ≥60 μF additionally exhibited V50s that were equivalent to the V50 of the single‐capacitor waveform (344 ± 65 V to 407 ± 50 V vs 339 ± 83 V). Conclusion : Defibrillation efficacy can be maintained in a full‐discharge, two‐capacitor waveform with the proper choice of capacitors.