The electrophysiologic effects of procainamide in the immature heart.

The electrophysiologic effects of procainamide in young animals have not been established. To test the effects of this drug on the immature heart, we studied eight nonsedated, chronically instrumented puppies (age range 12-28 days, median 16 days; weight range 0.7-1.1 kg, median 0.8 kg). The electrophysiologic study was performed before and 30 minutes after procainamide was given intravenously (20 mg/kg infusion). At the time of the study, the serum concentrations of procainamide (8.2 +/- 1.7 micrograms/ml to 6.2 +/- 1.6 micrograms/ml; mean +/- SEM) were in the usual adult human therapeutic range (4-10 microgram/ml). Procainamide in puppies caused a significant lengthening of the atrial and ventricular refractory periods, a significant decrease of the sinus node recovery time and the sinus of atrial echo zone, a significant decrease in the heart rate, and a significant increase in the sinoatrial conduction time.