Noninvasive prediction of efficacy of type IA antiarrhythmic drugs by the signal-averaged electrocardiogram in patients with coronary artery disease and sustained ventricular tachycardia

Abstract

This study attempted to determine if specific changes on the signal-averaged electrocardiogram (ECG) after type IA antiarrhythmic therapy are predictive of efficacy in the treatment of ventricular tachycardia (VT). Scalar and signal-averaged ECGs were obtained at baseline and after type IA drug therapy in 15 patients with coronary artery disease and inducible VT at baseline electrophysiologic testing. signal-averaged QRS duration, root-mean-square amplitude in the last 40 ms of signal-averaged QRS, and the duration under 40 μv of the signal-averaged QRS (low-amplitude signal), as well as ventricular effective refractory period at electrophysiologic study, and QTc on the scalar ECG were compared. At drug study, 6 patients (group A) had persistent but slower VT, whereas 9 (group B) had VT rendered noninducible. The baseline signal-averaged QRS duration was longer in group A than in B (136 ± 10 vs 115 ± 13 ms; p < 0.05), as was the scalar QRS (115 ± 19 vs 98 ± 11 ms; p < 0.05). After antiarrhythmic therapy, group A had a greater prolongation of both signal-averaged QRS (24 ± 10 vs 8 ± 3 ms; p < 0.05) and low-amplitude signal (31 ± 13 vs 3 ± 7 ms; p < 0.05), whereas group B had a greater increase in ventricular effective refractory period (49 ± 20 vs 20 ± 13 ms; p < 0.05) and corrected QT interval (100 ± 39 vs 43 ± 23 ms; p < 0.05). In conclusion, partial and complete responses to type IA drugs are associated with characteristic changes in myocardial conduction and refractoriness, the noninvasive measure of which may prove useful in guiding antiarrhythmic drug treatment.