ULTRASTRUCTURAL-CHANGES DURING CONTINUOUS RETROGRADE WARM AND MILD HYPOTHERMIC BLOOD CARDIOPLEGIA FOR CORONARY-BYPASS OPERATIONS

Ultrastructural changes in myocardial tissue were studied in 21 patients undergoing elective aorta-coronary bypass operation, The patients were randomized into two groups, with 10 of them receiving continuous retrograde warm and 11 continuous retrograde mild hypothermic blood cardioplegia, Biopsy specimens for electron microscopy were taken from the apical part of the left ventricle before and at the end of the aortic crossclamp period and after reperfusion of the myocardium. The ultrastructural changes were analyzed with use of a semiquantitative scoring system and classified as mild, moderate, or severe, Slight ultrastructural changes were found in both groups even before the aortic crossclamp period, At the end of the aortic crossclamp period the most prominent ultrastructural changes were mitochondrial swelling, damage of capillary endothelium, and clearing of the nucleoplasm or margination of chromatin, but some enlargement in intercalated discs was also discernible, Reperfusion of the myocardium for 15 minutes somewhat further increased the overall score of the ultrastructural changes, Two patients in the warm cardioplegia group had a perioperative myocardial infarction, and this may be one reason for the higher postoperative creatine kinase MB efflux in this patient group, Despite this finding, no major differences in the ultrastructural changes between the two cardioplegia groups could be observed. We conclude that only mild to moderate and principally reversible ultrastructural changes occur in myocardium during continuous retrograde warm and mild hypothermic blood cardioplegia for coronary bypass operation.