Nitinol Stent Loading On the Aortic Valve Complex

In order to obtain the contact forces between implanted aortic nitinol stents and the surrounding tissue, a finite element model of the CoreValve (Medtronic, USA) stent is developed. The deformed state of the stent in a patient after implantation is obtained using post-OP CT imaging. This point for point deformation map provides the basis to directly formulate kinematic boundary conditions for the stent model, or to interpolate the outer hull surface geometry of the deformed stent. This surface is used to perform a contact analysis where the stent is crimped and then released into the deformed shell. Both methods are implemented and compared by their contact force field output. The structural model of the stent uses a beam element formulation for numerical efficiency. The state of deformation after implantation shows large deflections and rotations of the structure, but the strains are within the linear elastic regime of nitinol. A linear elastic constitutive model is thus sufficient to analyze the implanted stent. Simulation of catheter crimping and deployment of the stent uses the super elastic material model by Auricchio (Auricchio and Taylor, 1997). Reconstructed force vector fields of individual patients are compared to the clinical outcomes of the procedures, in order to determine criteria for stent selection towards optimal clinical performance.