South African Flag Sign During Atrial Fibrillation: Physician Recognition of Acute Proximal Left Anterior Descending Artery Occlusion Despite No Automated ST-Segment Elevation Myocardial Infarction Alert.

The South African flag sign (SAFS) is a non-contiguous electrocardiographic pattern defined by ST-segment elevation (STE) in leads I, aVL, and V2 with reciprocal inferior ST-segment depression (STD), classically associated with first diagonal branch (D1) occlusion. We report a 58-year-old female presenting with acute chest pain and atrial fibrillation (AF), whose 12-lead electrocardiogram (ECG) demonstrated a SAFS phenotype. Automated ECG interpretation generated no ST-segment elevation myocardial infarction (STEMI)-specific alert, classifying the tracing as AF with possible subendocardial injury. This failure may have resulted from AF-induced RR variability combined with non-contiguous STE distribution outside standard algorithmic thresholds. Visual pattern recognition prompted STEMI pathway activation before hospital arrival. Coronary angiography confirmed acute thrombotic total occlusion of the proximal left anterior descending artery (LAD) with Thrombolysis in Myocardial Infarction (TIMI) 0 flow. Primary percutaneous coronary intervention restored TIMI 3 flow. The hospital course was complicated by severe left ventricular dysfunction, acute heart failure, and extensive microvascular obstruction. This case confirms SAFS as a rare but clinically meaningful phenotype and provides new diagnostic and angiographic insight by associating it with isolated proximal LAD occlusion, AF, and failed automated STEMI recognition. It suggests SAFS is not restricted to D1 occlusion, and visual ECG interpretation remains essential when automated systems fail.