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Sevoflurane and droperidol prolong the QT interval, and advancing age is not only associated with a prolongation of the QT interval but is also a risk factor for drug-induced QT interval prolongation. In this study, we compared the effect of sevoflurane and droperidol on the corrected QT (QTc) interval and the dispersion of ventricular repolarization (time interval from the peak to the end of the T wave [Tp-e]) in elderly patients with those in younger patients.Under sevoflurane anesthesia (1.5%–2.5%) with an antiemetic dose of droperidol (1.25 mg), the QT interval and the Tp-e interval, which indicates transmural dispersion of repolarization across the myocardial wall, were measured in 30 elderly patients (70 years and older) and in 30 younger patients (20–69 years) for 2 hours. The QT interval was normalized for heart rate (QTc) using 3 different formulas: Bazett, Matsunaga, and Van de Water. Data are presented as mean ± sd.The elderly group was 24.4 years older (P < 0.05) than the younger group. The QTc intervals in the 2 groups before anesthesia were not significantly different. Using all 3 formulas, the QTc interval in the elderly patient group was significantly prolonged by sevoflurane (the QTc intervals at preanesthesia and 60, 75, 90, and 120 minutes after sevoflurane exposure were 0.434 ± 0.028 seconds, 0.450 ± 0.037 seconds, 0.463 ± 0.037 seconds, 0.461 ± 0.037 seconds, and 0.461 ± 0.038 seconds, respectively, with the Bazett formula). The sevoflurane-induced QTc interval prolongation in the elderly patient group was significantly greater than that in the younger patient group (0.450 ± 0.037 seconds vs 0.432 ± 0.034 seconds, 60 minutes after sevoflurane exposure; 0.463 ± 0.037 seconds vs 0.441 ± 0.037 seconds, 75 minutes after sevoflurane exposure; and 0.461 ± 0.038 seconds vs 0.436 ± 0.030 seconds, 120 minutes after sevoflurane exposure with the Bazett formula), but the sevoflurane-induced QTc interval prolongation was neither further enhanced with time nor by droperidol. The Tp-e interval was not affected in either group.Sevoflurane causes greater QTc interval prolongation in elderly patients than in younger patients. Although sevoflurane does not affect the transmural dispersion of repolarization and sevoflurane-induced QTc prolongation does not advance with time and by droperidol administration, QT interval prolongation and its associated arrhythmias should be carefully monitored during sevoflurane anesthesia in elderly patients.