Optimal Small-Capacitor Biphasic Waveform for External Defibrillation

Abstract

Background —Biphasic waveforms have been reported to be more efficacious than monophasic waveforms for external defibrillation. This study examined the optimal phase-1 tilts and phase-2 leading-edge voltages with small capacitors (60 and 20 μF) for external defibrillation. We also assessed the ability of the “charge-burping” model to predict the optimal waveforms. Methods and Results —Two groups of studies were performed. In group 1, 9 biphasic waveforms from a combination of 3 phase-1 tilt values (30%, 50%, and 70%) and 3 phase-2 leading-edge voltage values (0.5, 1.0, and 1.5 times the phase-1 leading-edge voltage, V 1 ) were tested. Phase-2 pulse width was held constant at 3 ms in all waveforms. Two separate 60-μF capacitors were used in each phase. The energy value that would produce a 50% likelihood of successful defibrillation (E 50 ) decreased with increasing phase-1 tilt and increased with increasing phase-2 leading-edge voltage except for the 30% phase-1 tilt waveforms. In group 2, 9 waveforms were identical to the waveforms in group 1, except for a 20-μF capacitor for phase 2. E 50 decreased with increasing phase-1 tilt. Phase-2 leading-edge voltage of 1.0 to 1.5 V 1 appeared to minimize E 50 for phase-1 tilt of 50% and 70% but worsened E 50 for phase-1 tilt of 30%. There was a significant correlation between E 50 and residual membrane voltage at the end of phase 2, as calculated by the charge-burping model in both groups (group 1, R 2 =0.47, P <0.001; group 2, R 2 =0.42, P <0.001). Conclusions —The waveforms with 70% phase-1 tilt were more efficacious than those with 30% and 50%. The relationship of phase-2 leading-edge voltage to defibrillation efficacy depended on phase-2 capacitance. The charge-burping model predicted the optimal external biphasic waveform.