Influence of amiodarone on QT dispersion in patients with life-threatening ventricular arrhythmias and clinical outcome

Increased QT dispersion, defined as the difference between the maximum and minimum QT interval on the standard 12-lead electrocardiogram, is assumed to reflect regional inhomogeneity of ventricular repolarization and has been shown to be associated with an increased risk of arrhythmic events. The purpose of the present study is to examine the influence of amiodarone on QT dispersion in patients with life-threatening ventricular arrhythmias and to evaluate the predictive value of QT dispersion after amiodarone therapy for further arrhythmic events. ECG's were obtained in 47 patients 1–2 days before and 6–8 weeks after amiodarone was started. All patients had coronary artery disease with a mean EF of 34±14%. The QT interval was measured in each lead of a digitized ECG displayed on a high resolution monitor (250 mm s⁻¹). Amiodarone therapy resulted in a significant increase in the maximal QT_c interval (476±44 to 505±44 ms, p<0.001). However, measurement of QT dispersion (70±34 vs 73±29 ms) and Qtc dispersion (78±37 vs 77±31 ms) revealed no significant difference before and after amiodarone. During a one year follow-up period 26 patients were free of arrhythmic events and 7 patients developed further arrhythmic events. The remaining 14 patients were excluded from the one year follow-up analysis because of drug discontinuation (n=8), death due to heart failure (n=1), medical intervention (n=3) and incomplete follow-up (n=2). No measure of QT dispersion was predictive of recurrent arrhythmic events during treatment with amiodarone.

Conclusion: Treatment with amiodarone results in significant QT prolongation without altering QT dispersion. Measurements of QT dispersion were not predictive of amiodarone efficacy in this patient population.