EFFECTS OF AMIODARONE, SEMATILIDE, AND SOTALOL ON QT DISPERSION

To study the effects of class III agents on QT/QTc dispersion in patients with heart disease and cardiac arrhythmias, QT dispersion and QRS and RR intervals were compared in patients before and after treatment with amiodarone (n = 26), sematilide (n = 26), and sotalol (n = 26). QT, QRS, and RR intervals, and QTc values were calculated for each complex, and their mean values were calculated for each lead. QT and QTc dispersions were defined as differences between the minimal and maximal QT or QTc values in each of the 12 leads studied. Amiodarone, sematilide, and sotalol all significantly prolonged the QT interval and the QTc value. Significant reductions in QT and QTc dispersions were only found in the amiodarone group (QT dispersions: 79 +/- 13 vs 49 +/- 14 ms; p <0.001; QTc dispersions: 0.08 +/- 0.02 vs 0.05 +/- 0.01 s(1/2); p <0.001). The mean RR interval was significantly increased in patients after treatment with amiodarone (p <0.001) and sotalol (p <0.001), but not in patients receiving sematilide treatment (p >0.2). The baseline QT and QTc dispersions were significantly greater in patients with than without myocardial infarction before treatment (p <0.001). The mean baseline values for QT/QTc dispersions were not significantly different among all 3 groups. However, only amiodarone significantly reduced the QT dispersion (from 76 +/- 10 to 46 +/- 11 ms; p <0.001) and QTc dispersion (from 0.09 +/- 0.02 to 0.05 +/- 0.01 s(1/2); p <0.001) in patients with myocardial infarction. The reduction in the QT/QTc dispersion was significantly greater than that in patients without myocardial infarction (p <0.01). It is concluded that (1) antiarrhythmic agents that get by lengthening repolarization have differing effects on QT/QTc dispersion, most likely reflecting differences in their fundamental mechanisms whereby they prolong myocardial repolarization, and (2) the low reported incidence of torsades de pointes with amiodarone may in part be due to reduced dispersion of QT and QTc compared with other class III cents.