Introduction: Biphasic waveform defibrillation is not always more efficacious than monophasic waveform defibrillation.
Methods and results: Waveform efficacy appears to vary with the lead system used. In this prospective, randomized study, defibrillation efficacy with biphasic and monophasic single capacitor 120-microF, 65% tilt pulses was compared for a lead system consisting of right ventricular (RV), chest patch (CP), and superior vena cava (SVC) electrodes. Although this lead system is commonly used with monophasic pulses in transvenous defibrillators, few studies have examined the defibrillation efficacy of this lead system in man for biphasic waveform defibrillation. Fourteen cardiac arrest survivors undergoing defibrillator implantation were included in the study using pulses delivered from a cathodal RV electrode simultaneously to anodal SVC and CP electrodes. Biphasic and monophasic waveforms were recorded oscilloscopically to acquire defibrillation threshold (DFT) data on leading edge voltage requirements and for stored energy. The monophasic DFT voltage was 661 +/- 177 V compared to the biphasic DFT voltage of 451 +/- 185 V (P < 0.0001). The monophasic DFT stored energy was 28.0 +/- 13.4 J compared to the biphasic DFT stored energy of 14.1 +/- 12.4 J (P < 0.0001). The stored energy DFT was < or = 15 J in only 2 of 14 patients (15%) with monophasic defibrillation but < or = 15 J in 10 of 14 (71%) patients with biphasic defibrillation.
Conclusion: These findings indicate that biphasic defibrillation with an RV, SVC, CP transvenous electrode system is substantially more efficient than monophasic defibrillation, allowing for higher numbers of patients to receive transvenous defibrillators with a relatively simple lead system at a satisfactory cutoff DFT safety margin of 15 J.