1988 Volume 35 Issue 3 Pages 33-44
The technique “asymmetric biphasic stimulation” which paces the heart and neutralizes the post-stimulus polarization at the electrode-tiessue interface allows for the recording of the entire evoked endocardial response via a single electrode for both pacing and recording. Using this system the effects of antiarrhythmic drugs, procainamide and N-acetylprocainamide, on the myocardium were studied in 20 dogs. Before and during the five step drug infusion, the evoked endocardial responses were recorded during bipolar and unipolar at the rates of 120, 150 and 200/min. The plasma concentration of the procainamede ranged from 1.7 to 32.5 mg/l and that of N-acetylprocainamide ranged from 8.1 to 116.l mg/l. Procainamied significantly prolonged both the depolarization duration and the repolarization duration at a low plasma concentration (Class I antiarrhythmic drug property). N-acetylprocainamide significantly prolonged the repolarization duration at a low plasma concentration, while the depolarization duration was not significantly changed at a low or therapeutic plasma concentration (Class III antiarrhythmic drug property). The prolongacion of the depolarization duration by procainamide and N-acetylprocainamide was rate-dependent; the faster the rate the greater the prolongation. This simple and accurate assessment of the antiarrhythmic drug effects on the myocardium may provie a future means for the pharmacologic antiarrhythmic therapy.
