The rapid evolution of a myocardial infarction in an end-artery coronary preparation

The potential for salvaging infarcting myocardium depends on the time course of the infarction process. To determine the rate of infarct evolution in an end-artery coronary preparation similar to the coronary arterial system of the human heart, each of 84 swine underwent a reversible occlusion of the left anterior descending coronary artery for varying lengths of time, after which flow was reestablished into the occluded region for either 2 or 48 hr. Infarct size was assessed by nitro blue tetrazolium (NBT) staining and confirmed by histologic examination in the 48 hr animals. The region at risk of ischemic injury was determined by injection of monastral blue dye. Infarction progressed rapidly, with a mean of 1.9 +/- 1.5% of the risk region infarcting after 15 min of occlusion, 20.3 +/- 5.7% at 30 min, 43.3 +/- 4.8% at 45 min, 59.9 +/- 2.4% at 60 min, 70.6 +/- 1.7% at 90 min, 84 +/- 2.0% at 180 min, and 88.6 +/- 2.0% after 48 hr. Although there was good correlation in infarct sizing between NBT and histologic techniques at 2 and 48 hr of reperfusion, NBT underestimated infarct size at 15 and 30 min. These data suggest that in the setting of an end-artery coronary anatomy, reperfusion must be carried out within 90 min of coronary occlusion to achieve significant salvage of infarcting myocardium, a period of time much shorter than previously suspected.