Which statement about STEMI is most accurate?

• A. NSTEMI is diagnosed by ST elevation on ECG
• B. ST-segment elevation on ECG is the hallmark of STEMI
• C. ST-segment depression on ECG indicates STEMI
• D. Troponin elevation is not involved in diagnosing STEMI

Answer: (B)

ST-segment elevation on the ECG is the defining finding of STEMI because it shows transmural (full-thickness) myocardial ischemia from a suddenly occluded coronary artery. When ST segments are elevated in two or more contiguous leads, it signals that a large territory of the heart muscle is at risk and requires urgent reperfusion therapy (such as PCI or thrombolysis). Troponin is a useful marker of myocardial injury and helps confirm an infarction, but it does not by itself define STEMI; troponin can be elevated in NSTEMI as well, and early in STEMI it may still be normal. ST-segment depression or T-wave inversions indicate non-ST-elevation patterns, more consistent with NSTEMI or ischemia rather than STEMI.