Morphologic changes in atrial myocardial cells after cold cardioplegic standstill and during reperfusion in coronary bypass surgery.

Changes in the morphology of myocardial cells during reperfusion after long cardiac ischemia were studied as a sensitive indicator of myocardial damage. Observations were made by light and electron microscopy on specimens of atrial myocardium from 20 patients undergoing uneventful coronary bypass surgery with global hypothermic (less than 18 degrees C) cardioplegic protection. The findings in biopsy specimens taken before and immediately after cardiac arrest and following 20 and 60 min of reperfusion were arbitrarily graded in a semiquantitative scoring system. More than 60 min of cold cardioplegic arrest resulted in foci of altered myocardial structure, as seen in biopsies prior to reperfusion. After 20 min of reflow, intracellular and interstitial edema was found and no regression of the subcellular changes had taken place. (Worsening was observed in 7 cases.) After 60 min of reperfusion the myocardial ultrastructure had normalized in all the patients who had had ischemic cardiac arrest for less than two hours. In two hearts with longer ischemia (120 and 140 min), scattered areas of myocytes undergoing progressive changes were seen, although the postoperative myocardial performance was normal. Provided that the observed atrial changes were representative of left and right ventricle, the study indicates that reperfusion per se may enhance edema and cellular derangement, and that reperfusion for more than 20 min is usually necessary for normalization of the myocardium after more than one hour of ischemia.