INFLUENCE OF ANESTHETICS AND OF ARTERIAL BLOOD PRESSURE ON THE FUNCTIONAL REFRACTORY PERIOD OF ATRIOVENTRICULAR CONDUCTION

¹ Department of Pharmacology and Therapeutics, University of ManitobaFaculty of Medicine, Winnipeg, Manitoba, Canada

The effects of anesthetic doses of pentobarbital, thiopental, ether, halothane and cyclopropane on the functional refractory period of atrioventricular (A-V) transmission (FRP) were studied in spinal vagotomized dogs. All prolonged the FRP. The order of effectiveness was: thiopental > pentobarbital > halothane or ether > cyclopropane. The barbiturates slowed the heart more than did halothane and cyclopropane. Ether increased the heart rate in half the animals. Raising the arterial blood pressure prolonged the FRP both before and after the administration of the anesthetics, except after ether. In the case of ether, raising the blood pressure shortened the FRP. The results suggest that overall depression of A-V conduction, as evidenced by prolongation of the FRP, was not causally related to the appearance of arrhythmias in the presence of anesthetics which sensitize the heart to arrhythmias produced by epinephrine.