Importance of topical hypothermia to ensure uniform myocardial cooling during coronary artery bypass.

Recent reports have suggested that the delivery of cardioplegia to regional myocardium is impaired in patients with severe coronary artery disease. This study was designed to determine whether or not topical hypothermia is a necessary adjunct to systemic hypothermia and potassium cardioplegia to provide adequate cooling in regional myocardium supplied by stenotic or occluded coronary arteries. Twenty-two patients ranging in age from 47 to 68 years were included in the study. Patients were placed on bypass and cooled to 28° C. Temperature was measured over the right and left coronary artery distributions. The aorta was then cross-clamped and 1,000 cc of potassium blood cardioplegia, 5.7° to 11° C (mean 8.7°), was infused into the aortic root at a mean pressure of 99 mm Hg. Temperature was measured and 6 L of cold electrolyte (Plasma-lyte) solution, 2.3° to 5.1° C (mean 3.5) was poured over the heart into the pericardial well. The temperature measurements were then repeated. Myocardial temperature in regional myocardium supplied by normal coronary arteries after the injection of cardioplegia was less than 15° C. However myocardium distal to a severe stenosis or complete occlusion was significantly warmer (p