Early evolution from ischemia to myocardial necrosis.

The presence, age, and extent of myocardial ischemic injury can be determined with some precision using pathologic techniques. Electron microscopic studies can detect very early ischemic injury, only minutes old, even before irreversible injury (i.e., necrosis) is present; however, because of the small amount of tissue sampled, ultrastructural studies are not very useful for quantifying the size of the ischemic zone. Histologic studies can detect irreversible injury only hours old, and because large samples can be studied, the necrotic zone can be measured quite efficiently. In addition, the age of the infarct can be determined. The knowledge gleaned from such morphologic studies continues to contribute to the development of new diagnostic tests and therapies for patients with ischemic heart disease.