EFFECT OF AMIODARONE ON QT DISPERSION IN THE 12-LEAD STANDARD ELECTROCARDIOGRAM AND ITS SIGNIFICANCE FOR SUBSEQUENT ARRHYTHMIC EVENTS

Background and hypothesis: QT dispersion, measured as interlead variab ility of QT intervals in the surface electrocardiogram, has been demon strated to provide an indirect measurement of the inhomogeneity of myo cardial repolarization. The purpose of the present study was twofold: (1) to analyze the effect of amiodarone on QT dispersion measured in t he 12-lead standard EGG, and (2) to examine the association between QT dispersion on amiodarone and subsequent arrhythmic events. Methods: T o determine the effect of amiodarone on QT dispersion and its clinical significance for subsequent arrhythmic events, QT dispersion was meas ured in the 12-lead standard electrocardiogram (EGG) in 52 patients be fore and after administration of empiric amiodarone for ventricular ta chyarrhythmias. Results: QT intervals increased from 401 +/- 44 ms bef ore amiodarone to 442 +/- 53 ms after amiodarone therapy, and rate cor rected QT intervals (QTc) increased from 452 +/- 43 ms to 477 +/- 37 m s, respectively (p<0.01). QT dispersion, QTc dispersion, and adjusted QTc dispersion, which take account of the number of leads measured, we re not significantly different before and after initiation of amiodaro ne therapy (58 +/- 24 ms vs. 61 +/- 26 ms, 68 +/- 29 vs. 66 +/- 26 ms, and 22 +/- 8 vs. 22 +/- 8 vs, respectively, p = NS). During 31 +/- 25 months follow-up after initiation of amiodarone therapy, arrhythmic e vents defined as sustained ventricular tachycardia, ventricular fibril lation, or sudden death occurred in 11 of 52 study patients (21%). QT dispersion, QTc dispersion, and adjusted QTc dispersion on amiodarone were not different between patients with and without arrhythmic events during follow-up (65 +/- 14 vs. 59 +/- 29 ms, 73 +/- 15 vs. 64 +/- 28 ms, and 25 +/- 6 vs. 21 +/- 8 ms, respectively, p=NS). Conclusions: W e conclude that (1) amiodarone increases QT intervals and QTc interval s during sinus rhythm but does not significantly change measures of QT dispersion; and (2) QT dispersion measured in the 12-lead standard EC C after initiation of amiodarone therapy does not appear to be a usefu l marker for subsequent arrhythmic events.