Abstract
Background: Valve-in-valve (ViV) transcatheter aortic valve replacement in small surgical bioprostheses is often limited by residual gradients and prosthesis-patient mismatch. Implantation depth is operator-controlled, but depth guidance for different valve combinations remains limited. Objectives: The authors aimed to evaluate the effects of implantation depth on ViV hemodynamics, leaflet deformation, and pinwheeling in small surgical bioprostheses and to assess the mechanical consequences of THV underexpansion using accelerated wear testing. Methods: A 21-mm self-expanding transcatheter heart valve was implanted in five 21-mm surgical heart valves at multiple depths in a pulse duplicator. Mean gradient, effective orifice area, regurgitation volume, energy loss, leaflet deformation, and pinwheeling were assessed. Selected constrained ViV configurations underwent 200 million cycles of accelerated wear testing under ISO 5840 conditions. Results: Implantation depth substantially influenced ViV performance. In 3 porcine surgical valves, the most favorable combined hemodynamic profile occurred within a moderate-to-deep depth window of approximately 13.0 to 14.5 mm, although the optimal value differed across individual hemodynamic and deformation endpoints. Excessive depth increased frame constraint, leaflet distortion, and pinwheeling. Two bovine surgical valves showed mixed or U-shaped responses, consistent with differences in true internal diameter and transcatheter valve oversizing. The selected ViV configurations completed 200 million accelerated wear cycles without gross structural failure under bench conditions. Conclusions: In small ViV-transcatheter aortic valve replacement, the hemodynamic effects of implantation depth are valve-combination specific. A depth-window strategy may improve acute hydrodynamic performance, but clinical translation requires balancing hemodynamic benefit against leaflet deformation and durability-related uncertainty.