The Electrocardiogram in Ischemic Heart Disease
Reductions in blood flow (and consequently the oxygen supply) to the myocardium can cause transient or permanent damage (ischemia and necrosis, respectively). Atherosclerosis of the coronary arteries is the most common cause. In most cases, the ischemia initially involves the subendocardial layers of the myocardium, which are characterized by a higher metabolic rate and oxygen consumption than the subepicardial layers since they more exposed to extravascular compressive forces (systolic tension, ventricular filling pressure). Only later does the damage extends to the full thickness of the myocardium (Fig. 11.1).