QT interval of the ECG, heart rate and arterial pressure using propofol, methohexital or midazolam for induction of anaesthesia

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Abstract
The effects of propofol 2 mg/kg, methohexital 2 mg/kg or midazolam 0.3 mg/kg were studied on the QT interval of the ECG corrected by the heart rate (QTc), heart rate and arterial pressure during induction of anaesthesia in 87 ASA class I-(II)-patients. The patients were randomly allocated to one of the three anaesthetic groups. The incidence of the patients with a prolonged ATc interval (= more than 440 ms) ranged from 29 to 41% between the groups. In each group these patients were treated separately. After all anaesthetics, the QTc interval was significantly prolonged in the patients with a normal control QTc interval, whereas in the patients with a prolonged control QTc interval, it tended to be shortened both after propofol and methohexital and it was significantly shortened after midazolam. After injection of suxamethonium, no significant QTc interval changes occurred in the patients with a normal control QTc interval in either the propofol or the methohexital groups, whereas in the patients with a prolonged control QTc interval with propofol the QTc interval decreased significantly 60 s after suxamethonium when compared with corresponding preceding values. The mean values in the propofol group in the patients with a normal control QTc interval were always below the upper limit of the normal range. In the patients with a normal control QTc interval treated with midazolam, the QTc interval was significantly prolonged 60 s after suxamethonium and after intubation and in the patients with a prolonged control QTc interval treated with midazolam the QTc interval was significantly decresed after midazolam and increased 30 s after suxamethonium when compared with the corresponding preceding values. Only after methohexital did the heart rate increase significantly. A cardiovascualr intubation response occurred in all groups. The incidence of ECG changes ranged from 0 to 17% between the groups. There was no correlation between the incidence of ECG changes and prlongation of the QTc interval. On the basis of the present results, in the patients with a normal control QTc interval propofol and methohexital are superior to midazolam in situations in which prolongation of the QTc interval should be avoided. On the other hand, in the patients with a prolonged control QTc interval, midazolam is superior or at least equal to the other drugs. Due to a considerable increase of the heart rate, methohexital is inferior to propofol and midazolam.