Myocardial infarction without coronary occlusion. A morphologic study in sheep.

The macroscopic, histologic and enzyme-histochemical characteristics of the myocardial lesion obtained after heating of a thermoprobe in a branch of the left coronary artery in sheep is reported. In 13 sheep such myocardial lesions were produced distal to the location of the thermoprobe. Alterations were observed in accordance with generally accepted morphologic criteria for myocardial infarction. The coronary artery branch in which the thermoprobe was located showed erythrocyte and platelet aggregates immediately after the heating episode, which disappeared within a few min, as demonstrated by coronary arteriography. Injection of radiolabelled microspheres into the coronary circulation after induction of the myocardial lesion, cryosectioning of the heart and autoradiography revealed a lack of blood flow in the damaged myocardial region. We consider this new method a suitable tool for further studies on the complex pathology involved in the development of myocardial infarction.