DYNAMIC ANALYSIS OF DOFETILIDE-INDUCED CHANGES IN VENTRICULAR REPOLARIZATION

Objective: To use dynamic electrocardiographic (ECG) techniques to stu dy the influence of heart rate on dofetitide-induced QT prolongation a mong healthy volunteers, Background: The extent to which heart rate mo dulates QT prolongation induced by the new class III antiarrhythmic dr ug dofetilide is a matter of debate. Methods: Ten healthy volunteers u nderwent two 24-hour ECG recordings, one in the absence of dofetilide and the other after a single oral dose of 0.5 mg dofetilide. Two 4-hou r periods were defined during the second recording: Db, which correspo nded to stable high concentration of the drug, and D-1, which correspo nded to low concentration of the drug. Corresponding baseline recordin g periods, C-h and C-1, matched by time with Db and D1 were selected f rom the control ECG recording in the absence of dofetilide, QT versus R-R relations were compared in the presence and absence of dofetilide. The QT versus R-R relation slope was used as an index of the rate dep endence of QT prolongation, Rate-independent changes in QT duration al so were analyzed. Results: During D-h, dofetilide induced a mean 12% l engthening of ventricular repolarization. Dynamic ECG analysis showed that this prolongation increased as R-R cycles became longer, a phenom enon known as reverse rate dependence. However, QT prolongation persis ted at the shortest (600 ms) R-R cycle length that could be analyzed. During D1, dynamic ECG analysis showed a persistent, although small, e ffect of dofetilide on both QT prolongation (3%) and reverse rate depe ndence of this effect, Conclusions: Dofetilide prolongs QT duration, a nd this class III effect is influenced by heart rate, Although dofetil ide-induced QT prolongation decreases when the R-R cycle shortens, thi s reverse rate dependence is only partial because marked QT prolongati on persists at an R-R cycle of 600 ms. The results of our study indica ted that dynamic ECG techniques can be useful in detection of subtle, drug-induced changes in the duration of ventricular repolarization.