Prolongation of QT Interval During Induction of Anaesthesia

QT interval was studied in 156 adults and in 127 children during the induction of anaesthesia. Both in adults and in children, QT interval was prolonged statistically significantly after thiopentone 5 mg/kg and the most marked prolongation occurred after suxamethonium 1 to 1.5 mg/kg. In adults, d-tubocurarine 0.06 mg/kg, but not alcuronium 0.03 mg/kg or pancuronium 0.01 mg/kg, prevented statistically significantly the prolongation of the QT interval after suxamethonium 1.5 mg/kg. In children, all three muscle relaxants prevented statistically significantly the effect of suxamethonium 2 mg/kg and pancuronium also prevented the effect of thiopentone. The most common ECG changes were ventricular ectopic beats (VEB) which occurred in 26% of the adults and in 22% of the children who were not pretreated with the muscle relaxants. After pretreatment with d-tubocurarine, the incidence of VEB was 3% in both groups. In adults, alcuronium was as effective as d-tubocurarine in the prevention of VEB but in the alcuronium group supraventricular ectopic beats and junctional rhythm occurred in 6% and 9% of the patients, respectively. Pancuronium did not significantly prevent the incidence of VEB. On the basis of the present results, d-tubocurarine is the relaxant of choice for the prevention of the prolongation of QT interval as well as ECG changes during the induction of anaesthesia.