De Winter Is Coming: A Rare ST-Segment Elevation Myocardial Infarction (STEMI) Equivalent in an Ironman Competitor

De Winter's electrocardiogram (ECG) pattern, defined as upsloping ST-segment depression >1 mm at the J point with tall, symmetric T waves in the precordial leads, represents a rare acute ST-segment elevation myocardial infarction (STEMI) equivalent. Seen in only 2%-3% of proximal left anterior descending (LAD) occlusions, it is often missed by automated interpretation systems yet carries mortality similar to classic STEMI and mandates urgent reperfusion. We present the case of a 56-year-old male who collapsed during an Ironman triathlon after developing severe chest pain. Initial ECG showed hyperacute T waves in V2-V3, consistent with de Winter's pattern; high-sensitivity troponin was elevated. The patient underwent urgent catheterization, which revealed an acute mid-LAD occlusion and high-grade stenosis of the second diagonal branch. Primary percutaneous revascularization was performed with restoration of flow. Postprocedural echocardiography demonstrated moderately reduced left ventricular function, and the patient was discharged on guideline-directed medical therapy (GDMT) with an uncomplicated recovery. This case underscores the importance of recognizing de Winter's ECG pattern as a STEMI equivalent to facilitate rapid intervention and improve outcomes.