Vagus- and post-acetylcholine-induced changes in ventricular electrophysiology of the dog heart with and without beta-blockade.

Electrophysiologic effects of acetylcholine (Ach) injections were compared to those obtained by vagus stimulation with and without beta-adrenoreceptor blockade during right heart catheterization in 12 dogs. Monophasic action potentials were obtained by suction electrode technique, and programmed electrical stimulation was used to determine heart rate independent changes in 50 and 90% repolarization times and the effective (V-FRP) and functional (V-FRP) refractory periods of the right ventricle. Vagus stimulation decreased heart rate with and without beta-blockade, while after Ach injections a marked increase in heart rate was found, which could be eliminated by beta-blockade. Vagus stimulation increased action potential duration and refractoriness at high sympathetic tone induced by pentobarbital anesthesia, mainly by inhibiting the effect of beta-adrenoreceptor stimulation. It is concluded that stimulation of the vagus induces antiarrhythmic effects at high sympathetic activity, while the change in ventricular electrophysiology found after Ach injections in high doses to intact animals is an effect probably induced by stimulation of beta 1-receptors.