IS WARM RETROGRADE BLOOD CARDIOPLEGIA BETTER THAN COLD FOR MYOCARDIALPROTECTION

Background. This study tests the hypothesis that continuous normotherm ic retrograde blood cardioplegia is superior to cold intermittent bloo d cardioplegia in protecting the left and right side of the heart tran smurally during an extended cross-clamping period. Methods. Twelve ane sthetized, open chest dogs were placed on cardiopulmonary bypass and r andomized to receive continuous warm (n = 6) or intermittent cold card ioprotection (n = 6) during a 3-hour aortic crossclamp period. Transmu ral left ventricular muscle biopsy specimens were taken before the ini tiation of cardiopulmonary bypass and 90 and 180 minutes after crosscl amping. Right ventricular (RV) biopsy specimens were taken 180 minutes after aortic cross-clamping. Biopsy specimens were analyzed for adeno sine triphosphate, creatine phosphate, and lactate levels and for morp hologic changes via electron microscopy. Results. At the end of 180 mi nutes of cardiopulmonary bypass, the adenosine triphosphate contents o f endocardial and epicardial halves of the left ventricular myocardium were only slightly degraded in both cardioplegia groups; a significan tly greater reduction in adenosine triphosphate levels occurred in the RV of the warm compared with the cold group (p < 0.02). The differenc e in creatine phosphate values in the left ventricle between the cold group (35.2 +/- 23.4 nmol/mg cardiac protein) and the warm animals (64 .4 +/- 24.9 nmol/mg cardiac protein) was not statistically significant , but the RV creatine phosphate stores were significantly better prese rved in the warm compared with the cold cardioplegia group (p < 0.02). Lactate levels increased to a similar extent in both groups, but both values rose significantly over baseline (p < 0.03). Importantly the e lectron microscopic score of the left ventricle and RV indicated that tells were reversibly and not irreversibly damaged with both cardiople gic protections. Conclusions. These results suggest the following: (1) Chemical arrest is a major contributor of myocardial preservation dur ing diastolic arrest as used in clinical cardiac surgery. (2) Both met hods preserve the ultrastructure of the myocytes transmurally during 3 hours of aortic cross-clamping. (3) Both techniques protect the RV an d left ventricle; however, to provide optimal protection of the RV, al ternated retrograde and antegrade perfusion might be beneficial over r etrograde cardioplegia now alone, in particular with warm cardioplegia . (C) 1997 by The Society of Thoracic Surgeons