For each of these techniques, a gradient can be distinguished from minimal to small to large amounts of myocardial necrosis. Some clinicians classify myocardial necrosis as microscopic, small, moderate and large on the basis of the peak level of a particular biomarker.
Myocardial infarction is defined as myocardial cell death due to prolonged ischemia.
Cell death is categorized pathologically as either coagulation or contraction band necrosis, or both, which usually evolves through oncosis, but can result to a lesser degree from apoptosis. Careful analysis of histologic sections by an experienced observer is essential to distinguish these entities. It takes 6 h before myocardial necrosis can be identified by standard macroscopic or microscopic postmortem examination. Complete necrosis of all myocardial cells at risk requires at least 4 h to 6 h or longer, depending on the presence of collateral blood flow into the ischemic zone, persistent or intermittent coronary artery occlusion and the sensitivity of the myocytes. The pathologic identification of myocardial necrosis is made without reference to morphologic changes in the epicardial coronary artery tree or to the clinical history.