What would you expect to see on ECG in a STEMI?

• A. Chest pain with no ECG changes
• B. ECG changes, chest pain, and increased heart rate
• C. No ECG changes, chest pain, and increased HR
• D. ST-segment elevation in affected leads

Answer: (D)

ST-segment elevation in the leads that look at the affected region of the heart is the hallmark of a STEMI on ECG. This elevation happens because transmural (full-thickness) myocardial ischemia from an acute coronary occlusion creates an injury current that lifts the ST segment above baseline in those leads. Clinically, STEMI presents with chest pain and often a rapid heart rate, but the defining clue for this emergency is the ST-segment elevation pattern on the ECG in the territory supplied by the blocked artery. Other scenarios—chest pain with no ECG changes or chest pain with nonspecific changes—do not indicate STEMI, whereas ST elevation in the affected leads specifically points to this diagnosis. Note that in real life, additional features like reciprocal ST depression in opposite leads or new conduction abnormalities can be seen, and STEMI requires urgent reperfusion.