Effects of Practolol and Metoprolol on QT Interval, Heart Rate and Arterial Pressure during Induction of Anaesthesia

The effects of the selective beta 1-adrenergic receptor blocking agents, practolol with intrinsic sympathetic activity (ISA) and metoprolol without ISA, were studied on QT interval, heart rate, arterial pressure and cardiac arrhythmias during the induction of anaesthesia in 142 adults. In the control group, the QT interval was statistically significantly prolonged after thiopental, and the most marked prolongation occurred after suxamethonium. Neither practolol nor metoprolol alone affected the QT interval. Practolol 100 micrograms/kg i.v., but not 40 or 150 micrograms/kg i.v., almost completely reduced the prolongation of the QT interval after suxamethonium. In all doses of 20, 30 and 40 micrograms/kg i.v. metoprolol statistically significantly and dose-dependently reduced the prolongation of the QT interval after thiopental, suxamethonium and laryngoscopy, but the prolongation of the QT interval after intubation still occurred. Practolol and metoprolol alone statistically significantly reduced heart rate, but did not prevent the increase of heart rate after thiopental. The effects on arterial pressure were minimal. Neither practolol nor metoprolol prevented the cardiovascular intubation response. Ventricular ectopic beats after intubation occurred in 20% of the patients in the control group and their incidence ranged from 20 to 27% in the groups pretreated with practolol or metoprolol 20 micrograms/kg. In the groups pretreated with metoprolol 30 or 40 micrograms/kg, ventricular ectopic beats occurred in 5% and 8%, respectively. It is concluded that the selective beta 1-adrenergic receptor blocking agents practolol with ISA, and especially metoprolol without ISA, reduced the prolongation of the QT interval after suxamethonium.(ABSTRACT TRUNCATED AT 250 WORDS)