Transcatheter Edge-to-Edge Mitral Valve Repair for Severe Degenerative Mitral Regurgitation With Coexisting Cor Triatriatum Sinistrum.

BACKGROUND: Cor triatriatum sinistrum (CTS) is a rare congenital malformation, and its coexistence with degenerative mitral regurgitation (MR) in older adults is exceptionally rare and creates substantial technical challenges for transcatheter interventions. CASE SUMMARY: We report a 78-year-old woman presenting with progressive dyspnea, palpitations, and lower limb edema secondary to severe MR caused by posterior mitral leaflet prolapse. Preprocedural imaging incidentally identified a complete, nonfenestrated CTS membrane. Three clips were sequentially implanted at the prolapse site, downgrading MR from severe to trace. The final mean transmitral gradient was 3 mm Hg. The patient achieved rapid symptom resolution and was discharged 7 days postprocedure. DISCUSSION: This case establishes the feasibility of mitral transcatheter edge-to-edge repair in patients with CTS through meticulous preprocedural planning and controlled transmembranous access. It broadens the therapeutic landscape for anatomically complex, surgically prohibitive older adults with valvular disease. TAKE-HOME MESSAGE: The mitral transcatheter edge-to-edge repair is feasible and safe in MR with CTS.