Optimal small-capacitor biphasic waveform for external defibrillation - Influence of phase-1 tilt and phase-2 voltage

Background-Biphasic waveforms have been reported to be more efficacious tha n monophasic waveforms for external defibrillation. This study examined the optimal phase-1 tilts and phase-2 leading-edge voltages with small capacit ors (60 and 20 mu F) for external defibrillation. We also assessed the abil ity of the "charge-burping" model to predict the optimal waveforms. Methods and Results-Two groups of studies were performed. In group 1,9 biph asic waveforms from a combination of 3 phase-1 tilt values (30%, 50%, and 7 0%) 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 hel d constant at 3 ms in all waveforms. Two separate 60-mu F capacitors were u sed 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 wavef orms in group 1, except for a 20-mu F 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 th e 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-burpin g model predicted the optimal external biphasic waveform.