Thermokinetics of cold cardioplegic arrest

This study was designed to test the hypothesis that the rapidity with which the heart rewarms following cold cardioplegic arrest depends upon the technique of cannulation. In dogs, temperatures were monitored at multiple myocardial sites during rewarming, using four different cannulation techniques: caval cannulation with total bypass, caval cannulation with partial bypass, atrioventricular cannulation, and atrial cannulation. A mathematical model was constructed to facilitate analysis of the data, assuming that the rewarming process can be described by first order kinetics. Using this model, the half time of rewarming was defined as the time required for the myocardium to rewarm halfway from initial temperature to core temperature. Analyzing the several cannulation techniques in terms of the half time of rewarming, several conclusions were drawn: myocardial temperature distribution is non-homogeneous, rewarming is relatively rapid, partial bypass produces more rapid rewarming than total bypass, atrioventricular cannulation produces more rapid rewarming than either caval or atrial cannulation, and the principle routes of rewarming were from the posterior parieties and from blood entering the right side of the heart during partial bypass.