Early morphologic changes in cat heart muscle cells after acute coronary artery occlusion

The left descending coronary artery (LAD) was occluded in 16 open-chest cats for 10, 20, 40, or 60 minutes (four cats in each group). In addition, four sham-operated cats served as controls. Specimens for electron microscopy were obtained from the normal and ischemic zones, guided by in vivo injection of fluorescein, and verified by blood flow measurements with microspheres. The ultrastructure of 2,400 heart muscle cells and nuclei was studied. Fractional volumes of main cell components, mitochondrial surface density, and mitochondrial surface: volume ratio were calculated in 480 micrographs. After 10 minutes of ischemia we observed signs of sarcolemmal fragility, mitochondrial swelling, and lipid droplet accumulation. After 20 minutes of ischemia sarcolemmal fragmentation, chromatin clumping or margination and a maximal cytoplasmic edema were evident. The fractional volume of mitochondria was equally increased in ischemic zones of all groups. In both normal and ischemic zones there was a tendency toward smaller fractional volumes of lipid droplets during ischemia. In the normal zone there was mild cytoplasmic edema and slight mitochondrial swelling 10 minutes after occlusion as compared with the sham group. The present study demonstrates that a large proportion of cardiac myocytes undergoes severe damage within 20 minutes of coronary occlusion.