Ventricular fibrillation threshold for AC shocks of long duration, in dogs with normal acid-base state.

155-161. Earlier experimental studies of threshold ventricular fibrillating currents passing along the common accident pathway of forelimb to leg have shown a wide range of results for any one shock duration. In the present investigation the acid-base state of the experimental animals (dogs) was held within normal limits. It was found that whereas the mean minimum fibrillating current, 82·2μA for 3-second shocks, was within the values found by other workers, the range of results was reduced considerably to 67-101μA. Further, when the shock duration was increased, in stages, up to 60 seconds, again keeping the acid-base state within normal limits, the mean minimum fibrillating current did not alter markedly (being 80μA at 60 seconds) but the range of results progressively fell and was 73-88μA at 60 seconds. In the light of these findings the mechanism of ventricular fibrillation is discussed.