Efiect of Artificially Controlled Heart Rate on the Incidence of Ventricular Fibrillation in Hypothermia1

TORRES, J. C.,E.T. ANGELAKOS AND A.H. HEGNAUER. Effect ofartijcially controlled heart rate on the incidence of ventricular Jibrillation in hypothermia. Am. J. Physiol. 195(2): 437-439. [email protected] dogs were subjected to auricular and five to ventricular driving throughout the period of cooling. All animals in both groups succumbed to ventricular fibrillation at mean temperatures of 21.3OC and 20.3OC, respectively. These temperatures do not differ significantly from those for dogs with spontaneous heart action. Thus, abnormalities in S-A nodal rhythm or A-V conduction appear not to be contributory to fibrillation, since the one is eliminated by auricular driving and the other by ventricular driving. Intraventricular conduction times were assumed equal to the QRS duration. In both groups the conduction time increased linearly over the temperature range studied, and the slopes were parallel, suggesting that the limiting, temperature-sensitive process in conduction is the same for Purkinje system and myocardium. U NDER pentobarbital anesthesia approximately 60 % of dogs subjected to acute hypothermia terminate in ventricular fibrillation (VF) at heart temperatures of 25-19OC (I). Recently Riberi (2) and Riberi et al. (3) demonstrated that selective blockade of the S-A node with a local anesthetic provided protection against hypothermic VF. Such protection might be explained on the premise that in deep hypothermia there is no longer a regular discharge from the S-A node with the consequence that premature impulses arriving at the ventricle during relative refractoriness precipitate ectopic activity and fibrillation. If such were the explanation, then use of artificial pacemakers during hypothermia would lower the incidence of VF by insuring a constant rhythm for ventricular excitation.