Comparison of defibrillation efficacy using biphasic waveforms delivered from various capacitances/pulse widths

The efficacy of the biphasic waveform shock for the defibrillation of the ventricular myocardium has been reported by researchers and physicians. Although many authors have suggested that biphasic waveforms delivered from lower capacitances and shorter pulse widths could result in the reduction of the energy required for successful defibrillation, no report has described the smallest capacitance and pulse width yielding the lowest DFT. In this study, we compared efficacies of the biphasic waveform shocks and DFT safety margins among five different capacitances (175 mu f, 125 mu f. 100 mu f. 75 mu f, and 50 mu f) combined with 1-3 pulse widths. These experiments performed in six dogs used an endocardial lead/subcutaneous patch defibrillation electrode system. The average DFTs at E50 for 175 mu f (6.5/3.5 ms), 125 mu f (6.5/3.5 ms), 100 mu f (6.0/3.0 ms), 75 mu f (4.0/2.0) ms, and 50 mu f (3.0/2.0 ms) were 8.5, 10.0, 11.0, 14.0, and 16.5), respectively. These results indicate that a biphasic waveform delivered from a larger capacitance with a proper pulse width could achieve a higher defibrillation efficacy. All DFTs at E50 for all waveforms were compared to their deliverable energies and maximum stored energies. This comparison indicated a narrow DFT safety margin with capacitances below 100 mu f. Therefore, it is concluded that higher energy and higher leading edge voltage are required for a biphasic waveform delivered from a smaller capacitance with a shorter pulse width. Since the current capacitor technology provides a maximum voltage of 750 V using two capacitors in series, with the electrode impedance system used in this study, smaller capacitors appear to have a decreased probability of defibrillation success at a given energy.