Paired electrical stimulation: A Comparison of the effects on performance of the failing and nonfailing heart∗

Abstract The effects of paired electrical stimulation were compared in intact anesthetized dogs before and after barbiturate-induced myocardial depression. In the nondepressed state, paired electrical stimulation exerted a positive inotropic effect but tended to impair circulatory performance, lowering cardiac output and arterial pressure slightly. On the other hand, when applied during barbiturate-induced myocardial depression, paired stimulation elevated cardiac output by an average of 129 per cent, increased mean arterial pressure by 34 mm. Hg, and lowered mean right atrial pressure by 2.4 mm. Hg. The effects of paired stimulation were compared to those of acetylstrophanthidin and were found to be similar both in the failing and nonfailing heart. Thus, the effects of paired electrical stimulation are dependent on the circulatory state that exists at the time it is applied. The possible mechanisms responsible for the observed difference in effects in the normal and nonfailing heart were discussed.