[Effect of class I anti-arrhythmia agents on the signal-averaged ECG]

This study was designed to determine which parameters in the signal-averaged ECG are subject to the influence of class I antiarrhythmic agents and whether the effects on these parameters differ with respect to the various subgroups of agents within the class I antiarrhythmics. For this purpose, disopyramide was chosen as representative of class Ia, tocainide Ib and flecainide Ic. A total of 23 patients, twelve with coronary artery disease and eleven with dilated cardiomyopathy and high grade ventricular arrhythmics, received randomized and single-blind, placebo-controlled high single oral doses of 300 mg disopyramide, 800 mg tocainide and 300 mg flecainide with a washout period of five half-times of the antecedent drug prior to the subsequent agent. Before and two hours after the respective drugs the signal-averaged ECG was recorded. The position of the electrodes was unchanged throughout the study. A total of 142 recordings were performed. Computerized calculation of the duration and mean voltage of the entire filtered QRS complex and the voltage during the last 40 and 50 ms, respectively, was carried out according to the method of Simson. Additionally, according to a modification by Karbenn, the duration and voltage of late potentials were analyzed. In the baseline signal-averaged ECG, 13 of 23 patients (57%) had late potentials. Of the 18 patients who received disopyramide, ten had late potentials before and after the drug. In seven, late potentials were not present either before or after the drug. In one patient with a negative finding at baseline, late potentials were observed after disopyramide. There was a significant increase in the duration (p less than 0.001) as well as a decrease in the voltage of the entire filtered QRS-complex (p less than 0.01) and the voltage during the last 40 and 50 ms, respectively (p less than 0.05). Late potentials were present before and after tocainide in nine of 18 patients (50%) who received this drug. In the remaining 50%, late potentials were not observed either before or after the drug. Comparison of mean values before and two hours after 800 mg tocainide showed no significant changes for duration or voltage of the entire filtered QRS-complex nor for the voltage during the last 40 and 50 ms, respectively. Before and after flecainide, eight of 17 patients had late potentials (47%).(ABSTRACT TRUNCATED AT 400 WORDS)