Late thrombosis after an Amplatzer septal occluder in a child with multisystem inflammatory syndrome during the coronavirus disease 2019 pandemic

Multisystem inflammatory syndrome in children (MIS-C), a postinfectious complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is characterized by hyperinflammation and a prothrombotic state. Thrombosis involving intracardiac devices is rare but potentially life-threatening. We report a 16-year-old girl who had transcatheter closure of a fossa ovalis atrial septal defect using an Amplatzer septal occluder at 4 years of age. During the ongoing coronavirus disease 2019 pandemic, she presented with fever, rash, elevated inflammatory markers, and positive SARS-CoV-2 antibody testing. Transthoracic echocardiography revealed a large mobile thrombus attached to the interatrial septum near the device. She was diagnosed with MIS-C and managed with intravenous immunoglobulin, corticosteroids, and unfractionated heparin. Serial echocardiography showed resolution of the thrombus within 5 days, and she was discharged on low-dose aspirin. This case highlights late thrombus formation on an atrial septal occluder in the context of MIS-C, emphasizing the need for echocardiographic surveillance and anticoagulation in children with prior cardiac interventions who present with hyperinflammatory syndromes.