Ventricular defibrillation with triphasic waveforms

Background-It has been reported that triphasic defibrillation waveforms cau se less myocardial injury than biphasic waveforms. This study compared the defibrillation thresholds (DFTs) of triphasic and biphasic waveforms. Methods and Results-DFTs were determined for a transvenous lead system and a 300-mu F-capacitor defibrillator, In 8 pigs (group I), DFTs were determin ed for 5 triphasic waveforms with tilts of 80%, 83%, and 86% and for 1 biph asic waveform. DFTs were determined in another 8 pigs (group 2) for 2 triph asic and 4 biphasic waveforms with tilts of 43%, 49%, and 56%. In both grou ps, a biphasic waveform from a 140-mu F-capacitor defibrillator was also ev aluated, and both shock polarities were tested for each waveform. In group 1, with the 300-mu F-capacitor defibrillator, the lending-edge voltage and energy stored at DFT were significantly lower for triphasic waveforms with phase-duration ratios of 50/33/17 and an anode at the right ventricular ele ctrode for phase I than for biphasic waveforms (P<0.001). In group 2, the s tored energy of triphasic waveforms with 56% and 49% tilt was significantly lower than that of biphasic waveforms with the same tilts for anodal but n ot cathodal phase 1 at the right ventricular electrode. Electrode polarity significantly affected the DFT of triphasic waveforms for both studies. Conclusions-Some 80% tilt triphasic waveforms defibrillate more efficiently than biphasic waveforms with a 300-mu F-capacitor defibrillator. The triph asic waveforms for both groups were not superior to 140-mu F-capacitor biph asic waveforms. The efficacy of triphasic waveforms depends on phase durati ons and electrode polarity.