Mechanisms of ventricular fibrillation during hypothermia: Relative changes in myocardial refractory period and conduction velocity

Abstract

Summary Experimental studies of the effect of hypothermia on myocardial refractory period and conduction time during induced hypothermia have been performed. The following observations were made. 1. There was progressive and proportionate increase in refractory period and conduction time down to approximately 20° C. 2. At temperatures below 25° C., there was progressive impairment of conduction with development of partial and, subsequently, complete atrioventricular block with multifocal ectopic beats. 3. On the basis of these observations, it is felt that hypothermic ventricular fibrillation cannot be explained by disproportionate changes in conduction time and refractory period leading to re-entry of the impulse. This tends to refute the circus movement theory of fibrillation during hypothermia. 4. It is believed that hypothermic fibrillation at temperatures below approximately 25° C. is primarily a result of progressive interference with conduction, resulting in cessation of normal coordinated myocardial activation.