In acute pericarditis, the ECG changes are due to inflammation of which layer?

• A. Endocardium
• B. Myocardium
• C. Subepicardium
• D. Pericardium

Answer: (C)

In acute pericarditis, the ECG changes come from inflammation of the outer layer of the heart—the subepicardial region just beneath the epicardium that faces the pericardial sac. This inflammation creates a current of injury across the epicardial surface, leading to diffuse, typically concave-upward ST-segment elevations and concurrent PR-segment depressions in many leads. The pattern differs from a myocardial infarction, which usually shows localized ST elevations corresponding to a specific coronary territory and reciprocal changes due to deeper injury inside the heart muscle. Because the inflammatory process targets the outermost myocardium near the pericardium, the subepicardial layer is the best match for the source of these distinctive ECG changes.