Myocardial ischemia.

Myocardial ischemia results from an imbalance of energy supply and demand. Because of the essentially aerobic nature of myocardial metabolism and the high oxygen extraction from the blood, ischemia is usually equatable with limitation of blood supply. Coronary atherosclerosis is a patchy disorder, and therefore, ischemia usually occurs in segmental fashion throughout the topography of the heart. Ischemia is invariably seen earliest and most intensely in the deep or subendocardial layers of myocardium. Ischemia leads to biochemical disruption, including initiation of glycolysis, which in turn causes electrophysiological and mechanical disturbances. Myocardial ischemia can be induced naturally or experimentally in the human subject in a variety of ways, some of which have been studied in the laboratory.