Mitral Mass after Mitral Transcatheter Edge-to-edge Repair: Diagnostic Dilemma between Infective Endocarditis and Nonbacterial Thrombotic Endocarditis in a Patient with Malignancy

Transcatheter mitral valve repair using the mitral transcatheter edge-to-edge repair (M-TEER) technique is a well-established therapeutic option for patients with severe mitral regurgitation. However, postprocedural complications can pose diagnostic and therapeutic challenges. We report the case of an 80-year-old woman with multiple comorbidities, including essential thrombocythemia, and a newly diagnosed bladder neoplasm, who recently underwent M-TEER. During routine follow-up, a mass was detected on the atrial surface of the mitral clip. The initial suspicion was thrombus. Transesophageal echocardiography confirmed a mass on the mitral clip. 18F-fluorodeoxyglucose positron emission tomography/computed tomography showed focal uptake at the mitral valve level. Based on the modified Duke criteria and European Society of Cardiology 2023 guidelines, the diagnosis was considered "possible infective endocarditis." However, the concurrent neoplastic condition and lack of typical pathogens raised the alternative hypothesis of nonbacterial thrombotic endocarditis (NBTE). The patient was treated with intravenous anticoagulation and antibiotics. Serial imaging demonstrated a reduction in the size of the mass, but surgical intervention was precluded due to frailty. A definitive diagnosis could not be established.