The effects of second and third phase duration on defibrillation efficacy of triphasic rectangle waveforms

Biphasic waveforms are superior to monophasic waveforms for the termination of ventricular fibrillation (VF). However, whether triphasic waveforms are more effective than biphasic ones is still controversial. In the present study, we investigated the effects of second and third phase duration of triphasic rectangle waveform on defibrillation efficacy in a rabbit model of VF.

VF was electrically induced and untreated for 30s in 20 New Zealand rabbits. A defibrillatory shock was applied with one of the 7 waveforms: 6 triphasic rectangle waveforms and a biphasic rectangle waveform. The triphasic waveforms had identical first duration but with different second and third phase durations. A 5 step up-and-down protocol was utilized for determining the defibrillation threshold (DFT). After a 5min interval, the procedure was repeated. A total of 35 cardiac arrest events and defibrillations were investigated for each animal.

Two triphasic waveforms with identical first and second phase duration but shorter third phase duration had significantly lower DFT energy than biphasic waveform (0.57±0.18J vs. 0.80±0.28J, p=0.001; 0.60±0.18J vs. 0.80±0.28J, p=0.003). However, no statistical difference in DFT energy was observed between the two triaphsic waveforms that had identical phase duration but different voltages (0.57±0.18J vs. 0.60±0.18J, p=0.638).

Phase durations played a main role on defibrillation success for triphasic rectangle waveforms. The optimal triphasic rectangle waveforms that composed of identical second and first phase durations but with shorter third pulse were superior to biphasic rectangle waveform for ventricular defibrillation.