Ventricular Excitability During Hypothermia and Rewarming in the Dog. ∗

Abstract

Summary

All portions of the excitability cycle of the dog's ventricle suffer a progressive fall in threshold as body temperature is lowered to 25° under conditions of spontaneous respiration. The decrease in threshold is especially marked in early systole at a point designated as the minor dip. This general increase in myocardial irritability is a reversible phenomenon, the normal excitability recovery curve being reestablished by rewarming to normal body temperature. However, no change in ventricular excitability except at the major dip obtains during hypothermia provided the pH of the blood is maintained at a normal level throughout the cooling process. Both the total “refractory” period and the ventricular conduction time are prolonged during cooling and return to normal during rewarming.