EFFECTS OF POLARITY ON DEFIBRILLATION THRESHOLDS USING A BIPHASIC WAVE-FORM 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 eval uate the effect of the first phase polarity on the DFT of a biphasic s hock utilizing a nonthoracotomy ''hot can'' electrode configuration wh ich had a 90-mu F capacitance. We tested the hypothesis that anodal fi rst phase was more effective than cathodal ones for defibrillation usi ng biphasic shocks in ten anesthetized pigs weighing 38.9 +/- 3.9 kg. The lead system consisted of a right ventricular catheter electrode wi th a surface area of 2.7 cm(2) and a left pectoral ''hot can'' electro de with 92.9 cm(2) surface area, DFT was determined using a repeated ' 'down-up'' technique. A shock was tested 10 seconds after initiation o f ventricular fibrillation. The mean delivered energy at DFT was 11.2 +/- 1.7J when using the right ventricular apex electrode as the cathod e and 11.3 +/- 1.2 J (P = NS) when using it as the anode. The peak vol tage at DFT was also not significantly different (529.0 +/- 41.3 and 5 31.8 +/- 28.6 V, respectively). We concluded that the first phase pola rity of a biphasic shock used with a nonthoracotomy ''hot can'' electr ode configuration did not affect DFT.