Serum levels and electrophysiological effects of N-acetlyprocainamide as compared with procainamide in the dog heart in situ.

The electrophysiological effects of procainamide and its major metabolite N-acetylprocainamide were tested and compared on the heart of the anaesthetized dog by means of His bundle electrography and programmed electrical stimulation. Both drugs exerted a negative chromotropic effect. They also increased intra-atrial and intraventricular conduction times; procainamide was, however, the more potent of the two drugs. In contrast to procainamide, N-caetylprocainamide did not increase His-Purkinje and atrioventricular nodal conduction times, and at the lowest dose employed, atrioventricular nodal conduction times were decreased during atrial pacing. Both drugs increased the functional and effective refractory period of the right atrium and ventricle. N-acetylprocainamide increased the functional refractory period of the atrioventricular node, but to a lesser extent than procainamide.