New approach to biphasic waveforms for internal defibrillation: 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 d etermine 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 mu F) and phase-2 capacitors (1/3, 2/3, and 1.0 times the phase-1 capacitor) w ere tested and compared to a single-capacitor waveform (120 mu F, 65/65% ti lt) in a pig ventricular fibrillation model (n = 12, 23 +/- 2 kg), In the f ull-discharge waveforms, phase-2 peak voltage was equal to phase-1 peak vol tage. Shocks were delivered between a right ventricular lead and a left pec toral can electrode. E50s and V50s were determined using a ten-step Bayesia n process. Full-discharge waveforms with phase-2 capacitors of less than or equal to 40 mu F 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 greater than or equal to 60 mu F had an extremely hi gh 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 greater tha n or equal to 60 mu F additionally exhibited V50s that were equivalent to t he V50 of the single-capacitor waveform (344 +/- 65 V to 407 +/- 50 V vs 33 9 +/- 83 V). Conclusion: Defibrillation efficacy can be maintained in a full-discharge, two-capacitor waveform with the proper choice of capacitors.