Effect of antiarrhythmic therapy on delayed potentials detected by the signal-averaged electrocardiogram in patients with ventricular tachycardia after acute myocardial infarction

The ability of class I and class II antiarrhythmic drugs to either abolish delayed potentials or modify their timing was investigated in 39 patients with spontaneous ventricular tachycardia (VT) after myocardial infarction. Before the study all patients had delayed potentials on the signal-averaged electrocardiogram and inducible VT with programmed stimulation. These investigations were repeated during 67 trials of oral antiarrhythmic therapy (mexiletine 25, quinidine 24, metoprolol 13, disopyramide 2, procainamide 1, drug combinations 2). Delayed potentials were abolished in only 5 trails (7%), which was within the baseline variability of 8.5% for detection of delayed potentials. In the 7 trials in which VT inducibility was suppressed, delayed potentials persisted in 6 and mean ventricular activation time was virtually unchanged (151 ms before drug therapy, 152 ms after). Quinidine, mexiletine and metoprolol caused no consistent change in ventricular activation time. There was also no change in mean ventricular activation time (164 ms before and 163 ms after drug treatment) in patients in whom spontaneous VT did not recur with drug therapy during follow-up. Thus, the tested antiarrhythmic drugs had no consistent effects on presence or timing of delayed potentials on the signal-averaged electrocardiogram, even when VT inducibility was suppressed or recurrence of spontaneous VT was prevented.