Optimal biphasic waveforms for internal defibrillation using a 60 muF capacitor.

The optimal capacitance for defibrillation is calculated to be 40 to 80 muF by theoretical models, assuming a heart chronaxie of 2 to 4 ms and a mean impedance of 40 ohms. The 60 muF capacitor is optimal for providing maximum defibrillation efficacy, which can reduce defibrillation energy. The purpose of the present study was to determine the optimal tilt to maximize defibrillation efficacy in a 60/60 muF biphasic waveform and to compare these waveforms with an optimized 60/15 muF waveform. The defibrillation thresholds (DFTs) were evaluated for five different 60/60 muF biphasic waveforms having 40%, 50%, 60%, 70% and 80% phase 1 tilt and a 60/15 muF biphasic waveform having 50% phase 1 tilt with a hot can electrode system in 15 pigs (20+/-2 kg). Phase 2 pulse widths were held constant at 3 ms in all waveforms. The DFT was measured by 'down-up, down-up' technique and was random in each waveform. The DFT energy in 60/60 muF waveforms (40%, 50%, 60%, 70% and 80%) and a 60/15 muF waveform (50%) were 6.9*, 6.9*, 7.1*, 7.8*, 8.4* and 6.0, respectively (*P<0.05 versus 60/15 muF waveform). A phase 1 tilt of 40% to 50% maximizes defibrillation efficacy for biphasic waveforms using 60/60 muF capacitors. Additionally, switching to a 15 muF capacitor for phase 2 can further reduce the DFT energy.