Effects of doxapram on myocardial repolarization in anesthetized rats

The inhibitory effects of doxapram, a respiratory accelerator, on the cardiac impulse-conducting system and myocardial repolarization time were investigated in anesthetized animals using electrocardiography. Doxapram prolonged QT and QTcE which are indicative of the myocardial repolarization time, in a dose-dependent manner in rats anesthetized by sevoflurane. However, prolongation of the atrioventricular conduction time was not observed, even at the maximum dose (10 mg/kg), and deterioration of either the QT variability index or QT variability ratio, indices of time-dependent variation in cardiac cycle and myocardial repolarization, was not observed. Doxapram prolonged the myocardial repolarization time at high doses, but maintained the physiologically valid QT/RR relationship and did not increase proarrhythmia.