Differentiation between reperfusion and occlusion myocardial necrosis with technetium-99m pyrophospate scans

Although infarct-avid scanning is used to diagnose myocardial infarction, no distinction is made between two very different mechanisms of myocardial cell death. These are occlusion necrosis and reperfusion necrosis. The former is the major form of cell injury after a sustained occlusion of a coronary artery; the latter occurs immediately after reperfusion of ischemic myocardium. The present study examines whether the technetium pyrophosphate scan becomes positive more rapidly with one form of injury rather than the other. Myocardial damage was produced in dogs by either sustained coronary occlusion (Group I, 6 dogs) or reperfusion (Group II, 18 dogs). Infarct-avid myocardial scans obtained with technetium-99m pyrophosphate were positive in only one of six animals in Group I when isotope was injected 4.5 hours after sustained coronary occlusion. In contrast, 12 or 13 animals (Group IIa) with reperfusion necrosis had a positive scan when isotope was injected 3.5 hours after reperfusion. When isotope was injected only 30 minutes after the onset of reperfusion (Group IIb), only two of five scans were clearly positive. The results indicate that if the interval between myocardial injury and a positive scan is known, inference can be made concerning the predominant type of injury.