The only thing I can add to what Dr. Dowling has said is about the pig experiments, where 40-second applications used in pigs were associated with a higher rate of ventricular fibrillation. The only inference I would draw from that is that prolonged application is going to make it more likely that you'll have a discharge during that vulnerable period of the heart cycle, and the potential would exist then, perhaps more than in the briefer applications, for cardiac rhythm abnormalities. That, I think, physiologically would be the central concern.
On April 28th, 2008. See this statement in context.