Myocardial Infarction and Ischemia, I: ST Segment Elevation and Q Wave Syndromes

MYOCARDIAL ISCHEMIA Myocardial cells require oxygen and other nutrients to function. Oxygenated blood is supplied by the coronary arteries. If severe narrowing or complete blockage of a coronary artery causes the blood flow to become inadequate, ischemia of the heart muscle develops. Ischemia means literally “to hold back blood.” Myocardial ischemia may occur transiently. For example, patients who experience angina pectoris with exercise are having transient myocardial ischemia. If the ischemia is more severe, necrosis of a portion of heart muscle may occur. Myocardial infarction (MI) refers to myocardial necrosis (or, in nontechnical parlance—a “heart attack”). This discussion focuses primarily on ischemia and infarction of the left ventricle, the predominant pumping chamber of the heart. The important clinical topic of right ventricular infarction is also discussed briefly.