The use of evoked endocardial response for assessment of antiarrhythmic drug effects on myocardium.

The technique "asymmetric biphasic stimulation" which paces the heart and neutralizes the post-stimulus polarization at the electrode-tissue 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 procainamide ranged from 1.7 to 32.5 mg/l and that of N-acetylprocainamide ranged from 8.1 to 116.1 mg/l. Procainamide 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 prolongation 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 provide a future means for the pharmacologic antiarrhythmic therapy.