Atrial Repolarization as a Rare Mimicker of ST-Segment Elevation Myocardial Infarction

BACKGROUND: The identification of ST-segment elevations on a 12-lead electrocardiogram (ECG) is critical to the prompt management of myocardial infarction, but rare mimickers can lead to unwarranted cascade testing. CASE SUMMARY: A 25-year-old woman was admitted with severe hypoxia and was found to have uncorrected complex congenital heart disease. She underwent right heart catheterization and developed abdominal pain postprocedurally. A 12-lead ECG demonstrated inferior and lateral lead Q waves and ST-segment elevations. DISCUSSION: Given recent cardiac catheterization and presence of a large right-to-left intracardiac shunt, there was a concern for ST-segment elevation myocardial infarction (STEMI) from coronary artery embolism. An ECG was promptly repeated and showed normalization of ST segments. Her index ECG was felt to represent a low atrial ectopic rhythm with ST-segment elevations secondary to atrial repolarization. TAKE-HOME MESSAGE: Atrial repolarization is often indiscernible on the standard 12-lead ECG but can be evident in low atrial ectopic rhythms as ST-segment elevations, leading to misdiagnosis of STEMI.