Which of the following describes a complete occlusion in STEMI?

• A. Non-occlusive thrombus with partial flow
• B. Occlusion of the coronary sinus
• C. Complete occlusion of an epicardial coronary artery
• D. Occlusion of a peripheral artery

Answer: (C)

In STEMI, the defining event is a complete blockage of a coronary artery, cutting off blood flow to the heart muscle and causing transmural ischemia with ST elevations on ECG. The description that fits this best is a complete occlusion of an epicardial coronary artery, meaning a total blockage of the surface coronary vessel supplying the affected area. The other options don’t describe this scenario: a non-occlusive thrombus still allows some flow and is typical of NSTEMI or unstable angina; occlusion of the coronary sinus would affect venous drainage, not the arterial supply; and occlusion of a peripheral artery is unrelated to the coronary arteries and would not cause a STEMI.