Effects of N-Acetylprocainamide and Procainamide on Myocardial Contractile Force, Heart Rate, and Blood Pressure

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Abstract
The effects of N-acetylprocainamide (NAPA) and procainamide (PA) on myocardial force of contraction were compared in open-chest, vagotomized, pentobarbital-anesthetized dogs, with the use of a Walton-Brodie strain gauge sutured to the right ventricle. NAPA increased myocardial force of contraction, particularly at the high dose level (40 mg/kg). PA, had a negative inotropic effect that was equally apparent at all doses (10-40 mg/kg). Both NAPA and PA had a negative chronotropic effect and caused a reduction in mean arterial pressure. The mechanisms of the inotropic and hypotensive actions of NAPA require elucidation. Possible clinical use of NAPA as an antiarrhythmic agent are discussed.