Electrocardiographic studies on rats before and after cardiac arrest induced by hypothermia and asphyxia

¹ Department of Physiology and Cardiovascular Laboratories, State University of Iowa, Iowa City, Iowa

Eighteen rats were induced into hypothermia by the closed container technique to determine the effect of extreme reduction of body temperatures on the electrocardiogram. Complete cardiac arrest was obtained for an average time of 44 minutes with periods of ‘suspended animation’ averaging over 90 minutes. Thirty nine per cent of the animals were successfully resuscitated and survived for periods of at least 2 weeks. Andjus (J. Physiol. 128: 547, 1954.) employing a similar technique for induction of hypothermia was able to secure 50% survival with similar periods of suspended animation but the duration of cardiac arrest in his studies was not stated. Survival could not be predicted from the electrocardiographic record. The ventricular activation time showed an inverse relationship to the temperature. The QTc decreased with cooling and increased with warming. The heart rate decreased exponentially when the rats were cooled and apparently also increased exponentially when warmed.