Benefits of late coronary artery reperfusion on infarct expansion progressively diminish over time: relation to viable islets of myocytes within the scar.

To define the time limit and mechanism of the effects of late coronary artery reperfusion on infarct expansion, rats were randomized into one of four groups: permanent left coronary artery occlusion; and 2, 8, and 16 hours of left coronary artery occlusion followed by reperfusion. Two weeks after coronary occlusion, morphometric and histologic analyses were performed. Benefits of late reperfusion on infarct expansion progressively diminished after increasingly long periods of coronary occlusion and were minimal but present after 16 hours of coronary occlusion. The extent of the benefits of late reperfusion on infarct expansion were related to preservation and hypertrophy of small islets of still viable myocytes located mainly in the subepicardium of the scar.