The effect of propranolol intoxication on QTc interval in a canine model

The objective of this study was to evaluate the effects of propranolol intoxication on the QT and QTc intervals in a canine model. Lead II surface electrocardiograms were retrospectively evaluated from a previous study performed in this laboratory. Thirteen pentobarbital-anesthetized and instrumented animals, after a 30-min baseline period, were given 10 mg/kg dl-propranolol i.v. over 10 min. The electrocardiogram was printed continuously. Average heart rate and QT interval were measured and QTc was calculated at baseline and again 1 min after propranolol infusion was complete. Data for hemodynamic parameters have been previously reported demonstrating significant cardiovascular depression in all animals and one death with the administration of propranol. The QT interval was significantly prolonged by propranolol administration from baseline at 0.257 +/- 0.039 to 0.295 +/- 0.035 s. There was no significant difference in the QTc between baseline (0.371 +/- 0.026 s) and postpropranolol (0.366 +/- 0.021 s) measurements. In this canine model of propranolol intoxication, QT interval prolongation appears to be the result of associated bradycardia. Cardiovascular depression does not appear to include a significant direct effect on ventricular repolarization, as judged by the QTc interval.