What is the most common mechanism for acute myocardial infarction?

• A. Occlusion caused by coronary microemboli
• B. Thrombus development at a site of vascular injury
• C. From congenital abnormalities
• D. Severe coronary artery spasm

Answer: (B)

Disruption of an atherosclerotic plaque with rapid thrombus formation is the usual trigger for an acute myocardial infarction. When a vulnerable plaque tears, subendothelial collagen and tissue factor are exposed to blood, activating platelets and the coagulation cascade. The resulting rapid thrombus can acutely occlude a coronary artery, cutting off blood flow to a region of the heart and causing ischemia and eventual necrosis if not relieved.

This sequence explains why plaque rupture with thrombosis is the dominant mechanism behind most MIs. Other options—occlusion from coronary microemboli, congenital coronary abnormalities, or severe coronary vasospasm—can cause myocardial ischemia or infarction but are far less common as the primary mechanism.