Changes in the microvasculature of ischemic and infarcted myocardium.

The fine structure of the small vessels in experimental myocardial infarcts of 10- to 360-minute duration was studied in 32 dogs and compared with the appearance of the small vessels in the corresponding normal myocardium. Following 10 to 60 minutes of coronary artery occlusion, increasing numbers of endothelial cells showed a marked swelling which was consistent with the presence of an intracellular edema and frequently resulted in various degrees of obstruction of the vessel lumen. After 120 minutes of ischemia, not all endothelial cells were obviously swollen, but all showed signs of degeneration, including changes in organelles similar to those in surrounding muscle cells. A progressive intensification of degenerative changes, particularly with respect to the continuity of the endothelial lining and the integrity of the membrane systems of individual endothelial cells, was observed at 3, 4, 5, and 6 hours after coronary artery ligation, and cell debris could be seen in the lumina of most small vessels.