Unusual Native Valve Remnant in the Left Ventricular Outflow Tract After Valve-in-Ring Transcatheter Mitral Valve Replacement

<b>Background and clinical significance</b>. Valve-in-ring (ViR) transcatheter mitral valve replacement (TMVR) is an established therapeutic option for patients with failed surgical mitral valve repair at high surgical risk. Left ventricular outflow tract (LVOT) obstruction and prosthesis-related complications are well described, but other postprocedural findings remain poorly characterized. <b>Case presentation</b>. We report a challenging case of a persistent LVOT mass following ViR TMVR. A 78-year-old man underwent transapical ViR TMVR with a Sapien 3 valve for mitral stenosis. Early post-procedural echocardiography showed normal prosthetic function and no LVOT obstruction. During inpatient cardiac rehabilitation, transthoracic echocardiography revealed a mobile mass in the LVOT. The patient did not show any clinical, microbiological, or laboratory evidence of infection. Blood cultures were negative, and the mass showed no changes despite anticoagulation. Two- and three-dimensional transesophageal echocardiography demonstrated a mobile structure attached to the mitral prosthetic ring by a thin peduncle. After a comprehensive multimodality assessment, thrombus and infective endocarditis were considered unlikely. The mass was ultimately interpreted as a displaced remnant of the native anterior mitral leaflet. Given the prohibitive surgical risk and absence of complications, conservative management with echocardiographic follow-up was adopted. <b>Conclusions</b>. This case study emphasizes the role of advanced echocardiography and multimodality analysis in avoiding misdiagnosis and inappropriate therapeutic interventions.