Myocardial ultrastructure and contraction during short periods of experimental ischemia

The relationship of structure and function of the intact myocardium during the early minutes of experimental ischemia was studied in the anesthetized, open-chest pig. Regional contraction of ischemic and normal myocardium was measured, using isometric strain gauges on the anterior and lateral left ventricle. Biopsies for electron microscopy were taken consecutively 5, 10, 15, and 20 minutes after anterior descending artery occlusion-each followed by 10 minutes of reperfusion. Contraction of the ischemic area fell significantly within 15 to 30 seconds following occlusion, returning to 68, 50, 40, and 28%, respectively, after 5, 10, 15, and 20 minutes fo ischemia. In contrast, slight morphological changes were detected only after 5 and 10 minutes of ischemia, becoming more clear after 15 minutes, and unequivocal after 20 minutes-when return of contraction was minimal. The morphologic alterations in the ischemic area as seen by electron microscopy were: reduction of glycogen granules and specific changes in the mitochondria. The latter, consisting of swelling, disruption of cristae, and reduction of matrix, began to appear at 5 minutes and were more evident after 10 minutes of ischemia. These changes, although present, were not always proportional to sequential ischemic periods. This apparent lack of correlation between contraction and morphology could be due to sampling problems or to the focal nature of the ischemic process. However, it could imply that the changes seen by electron microscopy are a "late" phenomenon as compared to the loss of function. Morphologic corroboration of the immediate decrease of contraction of ischemic myocardium still escapes the perception of current morphological techniques. It is hoped that more refined stereological measurements will help bridge the present gap between function and morphology in early myocardial ischemia.