EFFECTS OF PROCAINAMIDE ON THE SIGNAL-AVERAGED ELECTROCARDIOGRAM IN RELATION TO THE RESULTS OF PROGRAMMED VENTRICULAR STIMULATION IN PATIENTS WITH SUSTAINED MONOMORPHIC VENTRICULAR-TACHYCARDIA

Objectives. The aim of this study was to assess the ability of the sig nal-averaged electrocardiogram (ECG) to predict the efficacy of procai namide. Background. The main role of the signal-averaged ECG has been the identification of postinfarction patients at risk of sudden death. Prediction of the efficacy of antiarrhythmic drugs represents another potential clinical application of this technique. Methods. The study examined the effects of procainamide on the time domain and spectral t emporal analysis of the signal-averaged ECG in relation to the results of programmed ventricular stimulation studies in 31 patients with ind ucible sustained monomorphic ventricular tachycardia. Results. Procain amide significantly prolonged the total and the initial QRS complex an d low amplitude signal durations (mean +/- SI) 135 +/- 30 vs. 161 +/- 46 ms, p < 0.0001; 87 +/- 16 vs. 98 +/- 20 ms, p < 0.0001, and 48 +/- 23 vs. 63 +/- 36 ms, p < 0.001, respectively) whereas the root-mean-sq uare voltage of the total QRS complex and of the last 40 ms of the QRS complex was significantly reduced (mean +/- SD 112 +/- 36 vs. 87 +/- 36 muV, p < 0.0001; 21 +/- 19 vs. 13 +/- 12 muV, P < 0.002, respective ly), The results of spectral temporal mapping of the signal-averaged E CG were similar before and after procainamide administration. Procaina mide prevented the inducibility of sustained ventricular tachycardia o r prolonged the cycle length of ventricular tachycardia by greater-tha n-or-equal-to 100 ms in 16 patients (52%) (responders). The fractional prolongation of the total QRS duration was significantly greater in r esponders (26 +/- 15%) than in nonresponders (10 +/- 10%) (p < 0.002) and, when this prolongation was greater-than-or-equal-to 15%, identifi ed responders with a sensitivity of 94%, a specificity of 87% and an o verall predictive accuracy of 90%.Conclusions. The effects of procaina mide on inducibility of ventricular tachycardia during programmed vent ricular stimulation can be predicted by the degree of drug-induced pro longation of the signal-averaged QRS complex.