QT interval of the ECG, heart rate and arterial pressure using five non‐depolarizing muscle relaxants for intubation

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Abstract
The QT interval, heart rate and arterial pressure were measured during anaesthetic induction in 186 patients without cardiovascular diseases or any preoperative drugs. The study was randomized and double‐blind. The patients were premedicated with either pethidine 1 mg/kg + atropine 0.01 mg/kg or with only pethidine 1 mg/kg i.m. Anaesthesia was induced with thiopental. After both types of premedication, either d‐tubocurarine 0.5 mg/kg, alcuronium 0.3 mg/kg, pancuronium 0.1 mg/kg, vecuronium 0.1 mg/kg or atracurium 0.5 mg/kg was injected after thiopental. Laryngoscopy was performed 4 min after the relaxant. The control values of the QT intervals (mean value 433 ms, range of the mean values 422–453 ms), were comparable. After thiopental, the mean values in the groups were no longer in the normal range (<440 ms). After atropine, the values at 3 min were statistically significantly prolonged in the pancuronium, atracurium and alcuronium groups, but not in the other groups, when compared with the values after thiopental. In the absence of atropine, no statistically significant prolongation of the QT interval occurred. After intubation in the absence of atropine, the values were statistically significantly prolonged in the alcuronium, pancuronium, vecuronium and atracurium groups and in the presence of atropine in the atracurium group when compared with the preceding values. The QT intervals were prolonged only in relation to the increased heart rate. At 6.5 min, the values in all groups were decreased to about the same level as before intubation. The mean control values of the heart rate were between 80 and 90 b.p.m. in the atropine‐treated groups and between 70 and 80 b.p.m. in the other groups. Before laryngoscopy, neither heart rate nor arterial pressure changed significantly in any of the groups. In all groups, a cardiovascular intubation response occurred. The incidence of cardiac arrhythmias ranged from 19% to 22% in the atracurium, pancuronium and vecuronium groups and from 0% to 3% in the other groups. Atropine did not affect the incidence of arrhythmias.