Myocardial Infarction Masking: A Rare Case of Coronary-Subclavian Steal Syndrome.

Coronary-subclavian steal syndrome (CSSS) is a rare but important complication following coronary artery bypass grafting (CABG) involving the left internal mammary artery (LIMA), typically due to proximal subclavian artery stenosis. We present a 54-year-old male with prior triple-vessel CABG (LIMA to left anterior descending) who developed acute chest pain and elevated troponin levels. Electrocardiogram showed diffuse ST-segment changes. Emergent angiography revealed patent grafts but critical 90% stenosis of the left subclavian artery proximal to the LIMA origin. The lesion was successfully treated with percutaneous angioplasty and drug-eluting stent placement, resulting in the resolution of symptoms and preserved cardiac function. CSSS, though uncommon, should be considered in post-CABG patients with recurrent angina or myocardial injury despite patent grafts. Literature estimates subclavian stenosis in up to 5% of CABG candidates, yet routine screening remains inconsistent. This case highlights CSSS as a reversible cause of ischemia and underscores the value of targeted vascular imaging in selected patients.