Ischemia-tolerance following cardioplegic arrest in human patients and in experimental animals

Cardiac biopsies were taken from the hearts of 40 patients undergoing open heart surgery for acquired and congenital disease. Tissue samples were taken prior to aortic cross-clamping, at the end of the ischemic period, and 20 minutes after reperfusion. Cardiac arrest was induced with Kirsch's cardioplegic solution at mild hypothermia (28-30 degrees C). Electron-microscopy of these tissue samples showed that cardioplegic arrest allows safe recovery with a tolerable degree of cellular alterations following ischemic periods of approximately 45 minutes. This period of reversible ischemia agreed well with similar studies in dogs that were completed by metabolic studies. ATP4-time in these dogs was 60 minutes under conditions closely resembling those at operationmin spite of the similarity between ischemia tolerance times, marked discrepancies existed on the ultrastructural level. Human hearts showed, generally, a much more marked degree of cellular alterations. The good correlation between ultrastructural alterations and the metabolic status of the canine heart can, therefore, not be used to predict levels of metabolites from human electron-micrographies.