ACCSAP CCKE Coronary Artery Disease (CAD): Risk Stratification and Prevention Practice Test

Most myocardial infarctions arise from rupture of a vulnerable plaque that is not severely narrowed, meaning the culprit lesion often has only modest stenosis. A plaque with a thin fibrous cap and a large lipid-rich core is prone to rupture; when rupture occurs, platelets aggregate and a thrombus forms, which can abruptly occlude the vessel and trigger an MI even if the baseline lumen narrowing was not severe. This is why data consistently show that many MIs originate from plaques with less than 50% stenosis.

So, the statement that most MIs occur in plaques with less than 50% stenosis captures the idea that instability and rupture, not the degree of narrowing alone, drive acute infarctions. In contrast, very high-grade stenosis (>70%) is more associated with chronic symptoms and may contribute to ischemia, but it is not the predominant driver of acute MI. MIs can occur without complete occlusion; a thrombus can cause infarction even if the artery is not fully occluded at the moment of the event. Plaque severity does influence overall risk, but the acute risk from rupture of a non-severely narrowed plaque is a key concept here.