The effects of antiarrhythmic drugs on the signal-averaged electrocardiogram in patients with malignant ventricular arrhythmias.

Late potentials arise from areas of slowly depolarizing myocardium and may represent the substrate for sustained VTs. Because they may be recorded from the body surface using signal-averaging techniques, they represent a noninvasive marker for potential malignant ventricular arrhythmias. The effects of antiarrhythmic drugs on the SAECG and late potentials are reviewed in this article. Unfortunately, there is no SAECG parameter (either total QRS, late potential, or frequency content) that appears to be useful in predicting drug efficacy. However, there are type-specific changes in global ventricular activation that can be quantified by the SAECG. These changes may be useful in categorizing the effects of new type I antiarrhythmic drugs. The effects of antiarrhythmic drugs on tachycardia cycle length are complex and probably represent combined effects of the drug on conduction and refractoriness. Such changes cannot be reliably categorized by the SAECG. Medical therapy of sustained VTs cannot be guided by the SAECG.