Flecainide-related alterations in the signal-averaged electrocardiogram: similarity between patients with or without ventricular tachycardia.

The signal-averaged electrocardiogram (SAECG) identifies patients at risk of sustained ventricular tachycardia (VT), but the influence of anti-arrhythmic agents on the SAECG is not yet established. We have evaluated the effects of flecainide on the SAECG (XYZ leads, high-pass filters 25 Hz and 40 Hz, noise level 0.2 microV-0.4 microV, Model 1200 EPX, ART) in 25 patients: 15 (VT group) had documented sustained VT (nine post-MI, two dilated cardiomyopathy, four normal hearts) and 10 (control group) had supraventricular arrhythmias and structurally normal hearts. The SAECG was recorded in all patients prior to, and 5 min following a flecainide infusion (2 mg.kg-1 over 10 min). Before flecainide administration an abnormal SAECG was recorded in six patients from the VT group and in no control patient. Following flecainide, 13 patients from the VT group and eight control subjects demonstrated abnormal SAECG. Flecainide produced similar significant percentage changes in all SAECG indices in both the VT and control groups: total QRS duration was prolonged by 26.0 +/- 10.4% vs 26.7 +/- 15.7%, late potential duration under 40 microV was prolonged by 55.5 +/- 62.0% vs 106.1 +/- 61.4%, and the root mean square voltage of the last 40 ms of the QRS was reduced by 42.1 +/- 34.9% vs 55.3 +/- 24.4%, respectively. We conclude that flecainide significantly changes the SAECG parameters in patients with and without a history of VT, irrespective of the underlying disease.