Unstable Coronary Syndromes

A cute coronary heart disease syndromes, including unstable angina, variant angina (Prinzmetal's angina), and acute myocardial infarction are usually caused by a primary decrease in myocardial oxygen delivery.'-15Both unstable angina and Prinzmetal's angina are caused by a primary reduction in myocardial oxygen delivery, but in all probability, the mechanisms responsible for the decrease in myocardial blood flow in these two syndromes are generally different.4 15 Unstable angina occurs in some patients with endothelial injury or ulceration at the site of a coronary artery stenosis6; some patients also have an intraluminal coronary artery thrombus.4-6,9-11 Specifically, Falk7 and Davies and Thomas8 have suggested that atherosclerotic plaque rupture or fissuring may lead to coronary arterial thrombi and the development of unstable angina, acute myocardial infarction, or sudden death. Patients with Q wave (usually transmural) myocardial infarcts often have ulcerated or fissured atherosclerotic plaques and the subsequent development of occlusive coronary artery thrombi.2,3 A similarity exists in the coronary arteriographic appearance in the relevant coronary artery in patients with unstable angina and in those patients who develop acute myocardial infarction.15 Patients with non-Q wave infarcts (usually subendocardial infarcts) much less commonly have coronary artery thrombi that are permanently occlusive,3 but these patients do have transient reductions in coronary blood flow followed by reperfusion.'6 The transient reductions in coronary blood flow may be related to