Abstract
<jats:p>Kounis syndrome is an acute coronary syndrome occurring in the context of an allergic, hypersensitivity, or anaphylactic reaction. Its established classification includes coronary vasospasm, coronary atherosclerotic plaque thrombosis, and hypersensitivity-associated coronary stent thrombosis. Coronary artery bypass graft (CABG) involvement has recently emerged as a potential fourth (Type IV) variant but remains poorly characterized, with evidence limited to a few published case reports. We performed a focused literature review to identify all published cases of suspected or confirmed Kounis syndrome involving arterial or venous coronary bypass grafts. The available evidence encompasses anaphylaxis-associated myocardial infarction due to saphenous vein graft thrombosis, hypersensitivity-related thrombosis of a drug-eluting stent implanted within a saphenous vein graft, diffuse vasospasm involving arterial and venous bypass conduits, and probable transient graft vasomotor dysfunction. These observations support recognition of bypass graft spasm and thrombosis as distinct manifestations of allergic coronary disease. Saphenous vein grafts appear particularly vulnerable because accelerated atherosclerosis, endothelial dysfunction, disturbed shear stress, and a highly thrombogenic substrate may amplify the consequences of mast-cell activation. Early recognition requires simultaneous assessment of the allergic reaction, native coronary arteries, and all bypass conduits. Electrocardiography, coronary angiography, serum tryptase, and, when appropriate, intracoronary imaging and thrombus histology may improve diagnostic confidence. This is the first review specifically dedicated to Kounis syndrome involving coronary bypass grafts. Although current evidence remains limited, this review provides a comprehensive synthesis of the available literature and identifies the major diagnostic and therapeutic knowledge gaps that should guide future investigations.</jats:p>