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Objective Sufficient stent radial expansion force is necessary in transcatheter aortic valve replacement (TAVR) to ensure proper valve anchoring. Due to the relatively high stent radial force, TAV leaflets are essentially mounted on a rigid frame. On the other hand, surgical bioprostheses are typically made from flexible stents to reduce stress at the commissures and improve valve longevity. The aim of this study was to compare leaflet stress distribution of a flexible frame surgical bioprosthesis with a rigid frame TAV using dynamic finite element analysis, considering tissue anisotropy.
Methods Since 23mm Edwards-SAPIEN XT leaflet geometry is similar to 23mm Carpentier-Edwards surgical bioprosthesis with flexible frame, 3D geometries of the valves were created for finite element simulations in ABAQUS/Explicit. An Elgiloy wire with a thickness of 0.75mm was considered as the frame of the surgical bioprosthesis. TAV frame was considered to be rigid. Leaflets were modeled as an anisotropic hyperelastic material based on the Fung’s strain energy. Furthermore for consistency, identical leaflet thickness of 0.5mm was considered for the TAV and the surgical bioprosthesis.
Results The maximum principal stress distributions of the 23mm TAV and surgical bioprosthesis in the peak of systole and diastole are shown in Figure1. During systole, high stress regions were primarily observed in the boundary edge. The maximum principal stress reached to 3.174 and 3.174 MPa in the TAV and surgical bioprosthesis, respectively. During diastole, however, high stress regions were primarily observed at the commissures. The peak of stress reached to 1.172 and 1.173 MPa in the TAV and bioprosthesis, respectively.
Conclusions Flexibility of surgical bioprosthetic frame was insignificant under physiological loading in contrary to what is being claimed. Our results indicate that leaflet stress distribution of the TAV with rigid frame was comparable to the same size surgical bioprostheses, considering identical tissue thickness. However, by reducing TAV leaflet thickness to minimize the cross-sectional area of crimped TAVs, higher leaflet stress distribution is expected which may lead to diminished long-term valve durability.