A 65-year-old woman with hypertension and dyslipidemia presented with rest chest pain in the setting of 2 mm ST depression in ECG leads V3-V6 and a troponin T level (TnT) of 0.92 ng/mL (normal, <0.08 ng/mL). Emergent cardiac catheterization, performed for the non-ST elevation myocardial infarction (NSTEMI), revealed a 60% proximal left anterior descending artery (LAD) bifurcation lesion involving an 80% lesion in the first diagonal branch (D1) and a 90% first obtuse marginal artery (OM1) lesion (Figure [A]). Fractional flow reserve (FFR) of the LAD was 0.78, and the LAD was successfully treated with a bifurcation approach using a 2.75×12 mm everolimus-eluting stent (EES, Xience Prime, Abbott Vascular, Redwood City, CA) in the LAD and a 2.25×20 mm EES (Promus Element, Boston Scientific, Natick, MA) in D1; both deployed at 10 atmospheres (atm). The OM1 was treated with a 2.25×12 mm EES (Xience Prime) deployed at 10 atm. Full details of coronary interventions are available in the Data Supplement. There was no angiographic evidence of dissection or incomplete expansion after stent placement. She was discharged on dual antiplatelet therapy.Seventeen days later, she presented again with chest pain, new anterior T-wave inversions on ECG, and TnT of 0.24 ng/ mL. Catheterization showed aneurysm formation at the LAD and OM1 stent sites with occlusion of a distal LAD branch (Figure [B]), suggestive of localized hypersensitivity vasculitis with thrombus formation within the aneurysm and embolization to the distal LAD. There were no systemic signs of hypersensitivity such as fever, leukocytosis, or eosinophilia. Given the short time frame of aneurysm formation, coronary artery bypass surgery was performed with a left internal mammary artery to the LAD and saphenous vein grafts to D1 and OM1. The LAD, D1, and OM1 were ligated distal to the stents to prevent further thromboembolism from the aneurysms. On gross examination of the heart surface during surgery, the epicardial tissue and fat were noted to be highly inflamed, erythematous, and indurated. The patient returned for surveillance catheterization 6 weeks later. This demonstrated a slightly diminished LAD aneurysm and occluded D1 and OM1 with patent grafts (Figure [C]).The patient presented again 4 months later with chest pain. ECG demonstrated ST depressions and T-wave inversions in V2-V6. TnT was 0.45 ng/mL. Emergent cardiac catheterization demonstrated significant enlargement of the LAD aneurysm. There were 90% in-stent restenoses proximal and distal to the aneurysm (Figure [D]). The D1 and OM1 remained occluded.Although the polymers used for drug-delivery in drug-eluting stents (DES) are highly biocompatible, they can rarely incite a severe inflammatory reaction consisting of eosinophils and lymphocytes involving all 3 arterial layers, leading to aneurysm formation and significantly increasing the risk of stent thrombosis.1 Hypersensitivity vasculitis has been noted with first generation DES [1][2][3] ; however, it has rarely been described after EES implantation 4 an...