Regional and transmural myocardial temperature distribution in cold chemical cardioplegia: significance of critical coronary arterial stenosis.

There is a growing recognition of discrepancies in myocardial temperatures during cold chemical cardioplegia. This study was designed to determine the extent to which coronary arterial stenosis just sufficient to abolish vasodilatory reserve in the working heart, but still compatible with myocardial viability ("critical stenosis"), limits heat transfer from the heart during cardioplegic infusion compared to complete coronary occlusion and no stenosis (control). In nine dogs, temperatures were measured from the subepicardium, midwall, and subendocardium of the left ventricle in the distributions of the circumflex (CCA) and left anterior descending (LAD) coronary arteries plus the aortic root, septum, mediastinum, and ventricular cavities. Cardiopulmonary bypass was instituted with core cooling to 28 degrees C. Three infusions of cold (4 degrees C), radioactive microsphere-labeled, potassium chloride arresting solution were periods of reperfusion. The data (mean +/- SEM) indicate that myocardial cooling was transmurally uniform under all conditions, but was significantly impaired (p less than 0.01) in the CCA region by both critical stenosis (17.4 degrees +/- 1.2 degrees C) and occlusion (23.6 degrees +/- 0.4 degrees C) compared to control (8.3 degrees +/- 0.5 degrees C), because of reduced perfusate flow to regional tissues (4 = 0.62, p less than 0.001). These findings show that coronary artery lesions, including those compatible with myocardial viability, impose a severe constraint on myocardial heat transfer and point to a need for improved cardioplegic technique.