What is the most common mechanism leading to acute myocardial infarction?

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

Answer: (A)

Most acute myocardial infarctions occur when an atherosclerotic plaque in a coronary artery ruptures. That rupture exposes thrombogenic material and underlying tissue, which rapidly activates platelets and the coagulation cascade. The result is a platelet-rich thrombus that forms at the site and occludes the artery, cutting off blood flow to heart muscle and causing infarction. This mechanism—thrombus formation at a site of vascular injury—best explains the common path to MI.

Other mechanisms exist but are far less common. Emboli from elsewhere can cause coronary occlusion but are an uncommon cause of MI. Congenital abnormalities and severe coronary vasospasm can lead to ischemia or infarction in specific situations, but they do not account for the majority of cases.