Reperfusion alters the relation between blood flow and the remaining myocardial infarction

This study evaluated whether or not reperfusion of ischemic myocardium 2 hours after occlusion alters the basic relation between myocardial blood flow and infarction occurring during permanent occlusion. Awake mongrel dogs chronically instrumented with proximal circumflex coronary occluders were subjected to permanent occlusion (group A, n = 10) or occlusion followed by reperfusion 2 hours later (group B, n = 11). Myocardial blood flow was quantified with radioactive microsphere injections before, 6 hours after occlusion (group A), immediately before release, and 4 hours after reperfusion (group B). Three days later, the dogs were killed, and the heart was sectioned systematically into approximately 80 1-2-g circumferential and transmural samples for radioactive counting and histologic infarct quantification. Epimyocardial and endomyocardial samples from the permanent occlusion group (A) and the reperfused group (B) were separated by infarct range and related to regional myocardial blood flow measurements. In groups A and B, regional myocardial blood flow in endomyocardial and epimyocardial layers were inversely related to the extent of infarction. For given degrees of infarction, myocardial blood flow was significantly higher (greater than twofold) in the reperfused group. Myocardial samples with extensive infarction (51-75%) showed only mild (20-30%) reductions in blood flow when compared with nonischemic regions in the reperfused group. Thus, although early reperfusion may salvage ischemic myocardium, these studies showed that reperfusion causes a new relation between blood flow to the ischemic region and eventual histologic infarct size. When myocardial blood flow is used as an index of myocardial salvage after reperfusion, the basic relation obtained from permanent occlusion studies substantially overestimates the extent of myocardial salvage and underestimates the degree of remaining infarction.