Rewarming rate of the myocardium during aortic cross-clamp time: variations with different levels of body hypothermia.

Twenty patients underwent elective cardiac valve replacement at 20 degrees C of body hypothermia. Temperatures of the ventricles of both walls were monitored on 12 different sites. Distribution of myocardial temperature ranged between 24.3 and 29.3 degrees C for patients of Group I before cardioplegia delivery and 13.2 degrees C in the septum after cardioplegic infusion. Average temperatures for the anterior and posterior wall were 13.6 C and 15 degrees C in the left ventricle and 14.7 and 15 degrees C in the right ventricle. Myocardial temperatures ranged from 26 to 28.7 degrees C for patients of Group II. After cardioplegic arrest, septal temperatures averaged 14.9 degrees C. The recorded sites of the anterior and posterior left ventricle were 14.1 and 13.1 degrees C. The effects of rewarming on the different myocardial areas occurred according to a logarithmic equation, which is faster in the first 10 minutes. The data suggest that the myocardium can be adequately protected with 25 degrees C hypothermia when the cross-clamp period is shorter than 60 minutes. When longer ischemic periods are expected, myocardial protection is best accomplished with 20 degrees C hypothermia.