Subacute Stent Thrombosis Related to Kounis Syndrome During Anaphylaxis Induced by Ultrasound Contrast Agent Infusion

Kounis syndrome (KS) is a rare condition characterized by acute myocardial infarction during an allergic reaction. It is classified into three subtypes based on pathophysiology. SonoVue, an ultrasound contrast agent that allows the evaluation of myocardial perfusion, is generally safe with a low incidence of severe adverse reactions. A 44-year-old man with a recent acute coronary syndrome treated with one stent implantation in the left circumflex artery underwent a contrast-enhanced stress perfusion echocardiography. Shortly after SonoVue administration, he developed diffuse rash, hypotension, tachycardia, and ultimately chest pain with an inferolateral ST-segment elevation myocardial infarction (STEMI) with 2:1 atrioventricular block. Coronary angiography revealed mild diffused coronary spasm and stent thrombosis at the proximal edge of the recently placed stent. After mechanical thrombectomy Optical Coherence Tomography was performed and revealed significant stent underexpansion and malapposition. The patient was treated with additional stent implantation in proximal overlap with the previously placed stent and he was discharged on the 7th post-operative day with a fully recovered left ventricular function. The case illustrates a rare combination of KS and an anaphylactic reaction to a contrast agent. The allergic reaction triggered type 3 KS with stent thrombosis and diffuse coronary vasospasm. Stent malapposition and underexpansion further facilitated thrombosis. Management included aggressive fluid resuscitation and norepinephrine, while epinephrine was avoided due to the risk of worsening coronary vasospasm. Serum tryptase levels were normal, possibly due to timing of sampling. Drug-coated balloon angioplasty was considered but it wasn't feasible due to stent undersizing.