Hemodynamic and Clinical Outcomes of Transcatheter Valve Expansion in Degenerated Mitral Bioprostheses

BACKGROUND: Transcatheter mitral valve-in-valve replacement is an established therapy for intermediate and high-risk patients with degenerated bioprostheses, but restricted transcatheter valve (THV) expansion within rigid surgical frames and elevated gradients have raised durability concerns. This study aimed to evaluate midterm outcomes of mitral valve-in-valve patients according to THV expansion and sizing strategy. METHODS: Patients who underwent mitral valve-in-valve with balloon-expandable valves at Mayo Clinic Rochester between 2014 and 2023 were retrospectively analyzed. THV expansion (inflow, waist, outflow) was measured from procedural fluoroscopy and indexed to nominal size, with zero indicating expansion to nominal dimensions. Median index values were used as subgroup cutoffs to compare the incidence of the primary composite outcome of all-cause mortality, heart failure readmission, and valve reintervention. RESULTS: The analysis included 80 patients with a median follow-up of 2.5 years. A total of 53 (66%) valves were underexpanded across all 3 diameters, with median inflow, waist, and outflow expansion indices of -10.2, -16.2, and -3.2, respectively. Across all indices, THV expansion closer to nominal size was associated with lower rates of the primary outcome (P<0.05). Greater expansion correlated with a larger mitral valve area and lower transvalvular mean gradient. Oversized THVs were significantly less expanded and had a higher incidence of the primary composite outcome compared with recommended-size THVs (P=0.02). CONCLUSIONS: THV underexpansion in degenerated mitral bioprostheses is common and associated with elevated gradients and worse midterm outcomes. Further research is warranted to define THV expansion targets to improve midterm outcomes following mitral valve-in-valve intervention.