Ultrastructural Evidence of Microvascular Damage and Myocardial Cell Injury After Coronary Artery Occlusion: Which Comes First?

SUMMARY Both microvascular damage and myocardial cell injury occur after coronary occlusion, but the relationship of these two events is unclear; specifically, it is unknown whether microvascular damage causes myocardial cell injury. Dogs were subjected to coronary occlusion for 20, 40, 60, 90 or 180 minutes, after which subendocardial and subepicardial biopsies were obtained for electron and light microscopy of 1-,u sec-tions. Of 312 biopsies of ischemic myocardium, 181 showed myocardial cell injury with no microvascular damage; 131 showed myocardial cell injury and microvascular damage; but none showed microvascular damage without myocardial cell injury. Although ultrastructural evidence of myocardial cell damage was pres-ent in the subendocardium after 20-40 minutes of ischemia, ultrastructural evidence of microvascular damage was not prominent until 60-90 minutes after coronary artery occlusion. Morphologic ultrastructural evidence of microvascular damage lagged behind myocardial cell injury, suggesting that ultrastructural microvascular damage is not a primary cause of ultrastructural myocardial cell injury. IN THE FIRST FEW HOURS after experimental coronary occlusion, morphologic ultrastructural ab-normalities occur not only in the myocardial cells, but also in the microvasculature.1 2 Some investigator