Myocardial ultrastructure and function during progressive early ischemia in the intact heart

Regional contraction of ischemic anterior and normal lateral left ventricular myocardium was measured with isometric force gauges after 5, 10, 15, and 20 minutes of anterior descending coronary artery occlusion-each followed by 10 minutes of reperfusion. Multiple myocardial biopsies of both regions were taken at these same intervals and examined by electron microscopic techniques. Mean contraction of the ischemic area fell significantly in 15 to 30 seconds and returned to an average of 68, 51, 40, and 28 per cent, respectively, after 5, 10, 15, and 20 minutes of ischemia. Simultaneously, focal morphologic changes were detected after 5 and 10 minutes, were more clear and widespread at 15 minutes, and diffuse and unequivocal at 20 minutes, when return of local contraction was minimal. The changes of myocardial morphology in the ischemic area as seen by electron microscopy were: reduced content of glycogen granules and mitochondrial changes. The latter began to appear at 5 minutes and consisted of swelling, disruption of cristae, and reduction of matrix. This study indicates a qualitative correlation between ultrastructural changes in regionally ischemic myocardium and diminished regional function in the intact heart. At 5 and 10 minutes the mitochondrial changes were focal, requiring multiple samples, while at 15 and 20 minutes they became more widespread, making the occasional sample more representative.