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

Frequency dependent effects of class I antiarrhythmic agents studied in patients with implanted pacemakers

Use and frequency dependency are common properties of Class I antiarrhythmic agents, which block cardiac sodium channels in vitro. The purpose of this study was to examine the rate dependent effects of Class I agents on ventricular conduction in humans in a crossover fashion. Twelve patients with implanted pacemakers who required antiarrhythmic therapy were studied. Four Class I agents were administered as follows: lidocaine, 1 mg/kg bolus followed by 4 mg/min infusion; disopyramide, 1 mg/kg bolus followed by 0.02 mg/kg per hour; aprindine, 1 mg/kg bolus followed by 4 mg/min infusion; and flecainide, 100 mg/day orally for 1 week. Trains of ventricular test stimuli between 70-180 ppm were applied during stable VVI pacing at 60 ppm. QRS duration was determined using signal-averaged as well as standard ECGs. Lidocaine produced significant QRS prolongation at rates > 110 ppm (3.0% +/- 1.4% at 120 ppm, P < 0.05; 7.2% +/- 1.8% at 180 ppm, P < 0.01). Aprindine, disopyramide, and flecainide produced significant QRS prolongation at rates as low as 70 ppm and in a frequency dependent manner: 12.7% +/- 1.5%, 9.6% +/- 1.6%, and 13.3% +/- 2.8% at 70 ppm, respectively, (P < 0.01); 21.6% +/- 0.6%, 14.7% +/- 2.4%, and 29.9% +/- 4.2% at 180 ppm, respectively, (P < 0.01). Time constants of the single exponential development of QRS prolongation when the pacing rate was abruptly increased to 150 ppm were 0.09 +/- 0.02 sec for lidocaine, 5.1 +/- 1.2 sec for aprindine, 8.1 +/- 1.7 sec for disopyramide, and 11.9 +/- 1.4 sec for flecainide.(ABSTRACT TRUNCATED AT 250 WORDS)

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.