Electrophysiologic properties of procainamide in man

Abstract

The electrophysiologic properties of procainamide were studied in 16 patients and correlated with plasma levels. Procainamide caused a minimal prolongation of atrioventricular (A-V) nodal conduction in 11 of 16 patients during sinus rhythm, but His-Purkinje conduction time was significantly prolonged in 15 of 16 patients. The effective refractory period of the atrium was prolonged by procainamide in 14 of 16 patients. The effective refractory period of the A-V node decreased in 8 of 9 patients. This may have been due to (1) anticholinergic properties of procainamide, (2) production of an A-V nodal “gap” by procainamide, or (3) an apparent A-V nodal block that actually represented decremental conduction in the His bundle; procainamide then caused delay in the A-V node allowing improved intra-His conduction and ventricular depolarization. The relative refractory period of the His-Purkinje system was prolonged in 10 of 11 patients. The effective refractory period was prolonged in one patient, unchanged in a second and apparently shortened in a third. In this third patient, procainamide produced a marked delay in proximal His-Purkinje conduction allowing a distal area of refractoriness to recover, thus causing apparent shortening of the effective refractory period. Plasma levels averaged 7.1 mg/ liter at the end of the study; no toxicity was noted.