Is the effectiveness of cardiac ventricular defibrillation dependent upon polarity?

Studies involving 240 fibrillation-defibrillation episodes via epicardial patch electrodes in 21-27-kg dogs and 480 transthoracic episodes in 100-kg calves are reported. In dogs, 120 episodes involving shocks by a 3.7-A, 5-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes of the reverse polarity. When the upper right ventricular patch was positive with respect to the left ventricular apex patch, 85% of the episodes yielded defibrillation; 78% defibrillated with the reverse polarity. In one series in calves, 120 episodes involving shocks by a 42-A, 4-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes involving the reverse polarity. In a second series, 59-A, 4-ms shocks were employed. In the 42-A series, 38% of the episodes were successful when the upper right electrode was positive with respect to the electrode over the apex, and 28% were successful with the reverse polarity. Corresponding results in the 59-A series were 80% and 68%, respectively. On an unpaired basis, the three p values were 0.19, 0.14, and 0.04, respectively. On a paired basis, all three comparisons yielded significant differences (p less than 0.05). We conclude that in these cases, at least, there is a moderate dependence upon electrode polarity and that our results appear to warrant clinical studies.