Effects of polarity on defibrillation thresholds using a biphasic waveform in a hot can electrode system.

The polarity of a monophasic and biphasic shocks have been reported to influence DFTs in some studies. The purpose of this study was to evaluate the effect of the first phase polarity on the DFT of a biphasic shock utilizing a nonthoracotomy "hot can" electrode configuration which had a 90-microF capacitance. We tested the hypothesis that anodal first phase was more effective than cathodal ones for defibrillation using biphasic shocks in ten anesthetized pigs weighing 38.9 +/- 3.9 kg. The lead system consisted of a right ventricular catheter electrode with a surface area of 2.7 cm2 and a left pectoral "hot can" electrode with 92.9 cm2 surface area. DFT was determined using a repeated "down-up" technique. A shock was tested 10 seconds after initiation of ventricular fibrillation. The mean delivered energy at DFT was 11.2 +/- 1.7 J when using the right ventricular apex electrode as the cathode and 11.3 +/- 1.2 J (P = NS) when using it as the anode. The peak voltage at DFT was also not significantly different (529.0 +/- 41.3 and 531.8 +/- 28.6 V, respectively). We concluded that the first phase polarity of a biphasic shock used with a nonthroracotomy "hot can" electrode configuration did not affect DFT.