Biomechanical modeling of transcatheter aortic valve replacement in a stenotic bicuspid aortic valve: deployments and paravalvular leakage

Abstract

Calcific aortic valve disease (CAVD) is characterized by stiffened aortic valve leaflets. Bicuspid aortic valve (BAV) is the most common congenital heart disease. Transcatheter aortic valve replacement (TAVR) is a treatment approach for CAVD where a stent with mounted bioprosthetic valve is deployed on the stenotic valve. Performing TAVR in calcified BAV patients may be associated with post-procedural complications due to the BAV asymmetrical structure. This study aims to develop refined computational models simulating the deployments of Evolut R and PRO TAVR devices in a representative calcified BAV. The paravalvular leakage (PVL) was also calculated by computational fluid dynamics simulations. Computed tomography scan of severely stenotic BAV patient was acquired. The 3D calcium deposits were generated and embedded inside a parametric model of the BAV. Deployments of the Evolut R and PRO inside the calcified BAV were simulated in five bioprosthesis leaflet orientations. The hypothesis of asymmetric and elliptic stent deployment was confirmed. Positioning the bioprosthesis commissures aligned with the native commissures yielded the lowest PVL (15.7 vs. 29.5 mL/beat). The Evolut PRO reduced the PVL in half compared with the Evolut R (15.7 vs. 28.7 mL/beat). The proposed biomechanical computational model could optimize future TAVR treatment in BAV patients. Graphical abstract.

Keywords: Bicuspid aortic valve; Computational fluid dynamics; Finite element; Paravalvular leakage; Transcatheter aortic valve replacement.

Fig. 1:

(A) Selected CT image of pre-TAVR calcified BAV patient (B) Extracted 3D calcium deposit volumes processed from the CT images with the proposed protocol (C) Previous calcium deposit volumes embedded inside the 3D-FE parametric BAV model with NFC angle of 140° (model 1) (D) Boundary mesh area between the leaflet and the calcium, with shared nodes assuming full interface displacement continuity

Fig. 2:

The Evolut R (left - model 2a) and Evolut PRO (right - model 2b) models. Both models are identical except for an additional outer cuff in the Evolut PRO

Fig. 3:

(A) Simulated FE Evolut stent crimping by applying a radial displacement on an outer cylindrical surface (Model 3) (B-D) Progressive deployment of the crimped stent (from model 3) inside the calcified BAV (model 1), by pulling the sleeve and tracking the stiffened and compliant BAV interactions with the stent (model 4)

Fig. 4:

(A) Stand-alone initial Evolut PRO geometry (model-2b) with cuff and bio-prosthetic leaflets (left column) (B) The deformed Evolut PRO model created by imposing the final deployed stent configuration from model-4 (BAV and stent) (middle column) (C) Deformed bio-prosthetic leaflets as a result of diastolic transvalvular pressure used to obtain the diastolic state, assuming fully compliant leaflets (right column- model 5)

Fig. 5:

Model 6: (A) The complete structural geometry, including the root, deformed native leaflets, deployed stent, cuff and closed bioprosthetic leaflets. The anchoring gaps between the device and the calcified leaflets are also presented (A3). (B) The CFD paravalvular leakage simulation model through the full TAVR-BAV structural assembly; also demonstrating the refined meshing by using the subgrid geometry resolution method. The pressure boundary conditions were employed in the aortic (inlet) and left ventricle (outlet) extensions

Fig. 6:

A summary of the consequential creation of models 1–6, which eventually resulted in a structural geometry of the deployed Evolut device inside the calcified BAV, at the diastolic phase. This geometry was imported into the CFD simulation.

Fig. 7:

The contact area between the deployed Evolut stent to the native cusps, including pressure values and total contact area with each cusp

Fig. 8:

Results of the CFD pressure and velocity contours indicating paravalvular leakage in the Evolut PRO for five deployment angles measured by clockwise and counterclockwise rotation in 24° relative to the 0° orientation, which represents alignment of the native and bioprosthetic commissures. The rotation is for both the cuff and the bio-prosthetic leaflets (first row). Second and third row illustrate pressure and velocity contours in planes BB’ and CC’, respectively. Last row indicates the PVL values for each case

Fig. 9:

Results of the velocity streamlines for the 0° and 48° orientations, in plane AA’. The leakage through the gap between the inner cuff and fused cusp is shown for the 48° case, while for the 0° orientation this gap is sealed.

Fig. 10:

Results of the pressure (first row) and velocity (second row) contours comparing the Evolut PRO (left) and Evolut R (right), for cuff orientation case of 0°, in the cross sectional planes AA’ (presented in Fig. 5B.1) and BB’. Last row indicates the PVL values for each device