Sensitivity of the Hypothermic Myocardium to Calcium

Abstract

The susceptibility of the dog heart to ventricular fibrillation (VF) induced by CaCl 2 infusions is several fold greater in hypothermia than in normothermia, i.e., both the amount of CaCl 2 infused and the terminal plasma levels are found to be less in hypothermia. Dogs rendered hypercalcemic prior to hypothermia induction also succumb to ventricular fibrillation, and at relatively high heart temperatures (22-27 C.), whereas those rendered hypocalcemic by Na-EDTA infusions succumb to asystole at much lower temperatures (14-18 C.). The calcium sensitivity is not pH dependent either at normal or low temperatures.