oa Finite Element Modeling of Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR) has revolutionized treatment for inoperable and high risk surgical patients with severe symptomatic aortic stenosis. Transcatheter aortic valves (TAVs) are deployed within the native diseased valve without sutures to secure them within the annulus. Oversizing of TAVs with respect to the annulus size is required to achieve appropriate anchoring. Optimal TAV function requires expansion of the frame to its nominal dimension. However, clinically TAVR results routinely in incomplete expansion of the stent frame. We have previously demonstrated that significant under-expansion results in suboptimal TAV function with impaired coaptation of TAV leaflets, but precise characteristics of TAV leaflets and frame after implantation have been poorly studied. The aim of this study was to determine the effect of TAV under-expansion as observed clinically on stress distribution and magnitude in the TAV stent and leaflets using finite element (FE) modeling. A computer aided design (CAD) model of a TAV was developed based on the 23mm Edwards-SAPIEN design and used to create a finite element (FE) model. The 3D model consists of a stent, three pericardial leaflets, a clamp compression unit and an expandable balloon. Large deformation FE simulations were conducted to model the TAVR procedure, including TAV crimping followed by balloon-expansion to 17, 21, and 23mm. Stress distribution on the stent and leaflets were determined. As the post-inflation diameter increased, the von Mises stress on the TAV stent decreased. The maximum von Mises stresses of stent after expansion to 17, 21, and 23mm were 365, 346, and 262 MPa, respectively. However, unlike the stent, the leaflet stress increased as the post-inflation diameter increased. The peak von Mises stresses after expansion were 1.5, 1.3, and 2.4 MPa, respectively. We present the first FE simulation which was developed to model the TAVR procedure from crimping and balloon inflation of the TAV. Stress on stent and leaflets after implantation is dependent on the internal diameter of the inflated stent. While stress on the stent decreases with increasing TAV expansion, stress on the leaflets increases. FE modeling can be further applied evaluate whether a specific TAV size and design is optimal for a specific patient.