What is the purpose of the 12-lead ECG in the context of STEMI?

• A. Evaluate chest X-ray
• B. Measure blood pressure
• C. Localize infarct territory by viewing multiple heart regions
• D. Assess oxygen saturation

Answer: (C)

The main idea is that a 12-lead ECG uses multiple viewpoints of the heart’s electrical activity to map where a STEMI is happening. By recognizing ST-segment elevations (and reciprocal changes) in specific leads, you can infer which region of the heart is infarcted. For example, elevations in the inferior leads point to an inferior wall infarct, usually supplied by the right coronary artery, while elevations in anterior leads indicate an anterior infarct supplied by the left anterior descending artery, and lateral leads point to a lateral infarct. Posterior infarcts may show changes that require posterior leads or reciprocal changes in the front leads. This localization is crucial for guiding urgent reperfusion decisions and preparing the catheterization lab. The other options aren’t the purpose of the ECG in STEMI—they relate to imaging or vital signs, not the electrical assessment provided by the ECG.