Clinical meaning
Acute coronary syndrome (ACS) encompasses unstable angina (UA), NSTEMI, and STEMI, all resulting from atherosclerotic plaque rupture or erosion with superimposed thrombosis. Plaque rupture exposes the lipid-rich necrotic core and collagen to flowing blood, triggering platelet adhesion (via von Willebrand factor and GPIb), activation, and aggregation (via GPIIb/IIIa). The coagulation cascade generates thrombin and fibrin, forming an occlusive or near-occlusive thrombus. STEMI results from complete thrombotic occlusion causing transmural ischemia (ST elevation); NSTEMI results from subtotal occlusion or microembolization causing subendocardial injury (troponin elevation without ST elevation); UA involves ischemia without myocyte necrosis (normal troponin). Risk stratification uses HEART score (History, ECG, Age, Risk factors, Troponin) or TIMI score to guide disposition.