Structural changes in myocardium during acute ischemia

Abstract

The structural occurring occuring in severely ischemic myocardial cells were described as a function of the duration of ischemia. Tissue for study was obtained from dog myocardia following acute occlusion of a major branch of a coronary artery. Ischemia was defined as being present when arterial flow was insufficient to maintain aerobic metabolism and was described as 'total' (no flow), mild (Anaerobic metabolism present but flow sufficient to allow cells to survive), and severe (marked anaerobic metabolism because of low flow; cell death occurs if ischemia persists). Characteristic structural changes were found in severely ischemic myocardial cells after 30 to 40 min of coronary occlusion. These changes included virtual depletion of glycogen supplies, relaxation of myofibrils, and nuclear and mitochondrial changes. The mitochondria were swollen, exhibited decreased matrix density, and developed amorphous densities in the matrix space. These densities increased in size and number as the period of ischemia was prolonged. Mitochondria exhibiting these changes were very fragile and showed marked functional defects. The effect of reperfusion of the area of ischemia with arterial blood was described in detail. Reversibly injured cells resumed contractile function quickly after reperfusion. Irreversibly injured cells, on the other hand, swelled enormously after only 2 min of reflow. They also accumulated Ca2+ in mitochondria and had marked contraction bands. These findings suggest that failure of cell volume regulation may be one of the earliest signs of the development of the irreversible phase of ischemic injury.