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* Anatomy of Plaque Disruption Atherosclerotic plaque rupture is the major cause of thrombosis of the coronary arteries that leads to acute ischemia and AMI.1 Plaques can be categorized as either vulnerable or stable based on their structural characteristics.2,3 Atherosclerotic plaques prone to rupture are commonly composed of a mass of soft lipids with abundant cholesterol crystals separated from the vessel lumen by a thin fibrous cap.4 Accumulation of foam cells and lipids promotes plaque instability.5 If the extracellular lipid core makes up more than 40% of the overall plaque volume, the plaque is particularly susceptible to rupture.4 Stresses from intraluminal pressure, coronary vasomotor tone, tachycardia (which increases cyclic stretching and compression), and rupture of the small nutrient vessels (vasa vasorum) in the walls of large blood vessels can combine to rupture a plaque, usually at the margin of the fibrous cap near an adjacent plaque-free segment of the coronary artery wall (shoulder region of the plaque).3,5 1. Meyer BJ, Chesebro JH. Aspirin and anticoagulants. In: Julian DG, Braunwald E, eds. Management of Acute Myocardial Infarction. Philadelphia, PA: WB Saunders Co.; 1994:163-192. 2. Libby P. Molecular bases of the acute coronary syndromes. Circulation. 1995;91:2844-2850. 3. Antman EM, Braunwald E. Acute myocardial infarction. In: Braunwald E, ed. Heart Disease, A Textbook of Cardiovascular Medicine. Philadelphia, PA: WB Saunders; 1997:1184-1288. 4. Fernandez-Ortiz A. Fuster V. Evolution of the atherosclerotic plaque. In: Rifkind BM, ed. Lowering Cholesterol in High-Risk Individuals and Populations. New York, NY: Marcel Dekker, Inc.; 1995:69-98. 5. Langer A, Armstrong PW. Treatment of acute ischemic syndromes in the absence of coronary occlusion: preventing progression to acute occlusion. In: Braunwald E, Califf RM, eds. Atlas of Heart Diseases. Acute Myocardial Infarction and Other Acute Ischemic Syndromes. New York, NY: Mosby; 1996;