COMPARISON OF ELECTROPHYSIOLOGIC EFFECTS OF QUINIDINE AND AMIODARONE IN SUSTAINED VENTRICULAR TACHYARRHYTHMIAS ASSOCIATED WITH CORONARY-ARTERY DISEASE

Fifteen patients with spontaneous ventricular tachyarrhythmias underwe nt electrophysiologic studies at baseline and during therapy with quin idine and amiodarone. In 9, ventricular tachycardia (VT) with a simila r QRS morphology was induced with quinidine, amiodarone and under the control state. Both quinidine and amiodarone significantly increased Q RS duration and the VT cycle length. Amiodarone increased the VT cycle length more than quinidine (85 vs 121 ms, p < 0.05). Amiodarone incre ased the percent QRS duration (during sinus rhythm, ventricular pacing and VT) significantly less than percent VT cycle length, whereas quin idine did so only at slow rates (at faster rates the percent increase in QRS duration is not different from the percent increase in VT cycle length). The percent increase in QRS duration produced by quinidine c orrelated significantly with the percent increase in VT cycle length ( the best correlation was observed during pacing, r = 0.78). In contras t, no such significant correlations were obtained for amiodarone. Thus , amiodarone prolongs VT cycle length more than quinidine (at the dose s used). The effects of quinidine on conduction in tissue mostly unrel ated to tachycardia origin predict effects in the tachycardia cycle le ngth. In contrast, the effects of amiodarone on the latter are more in tense but not predicted by those on tissue unrelated to the tachycardi a origin.