Comparison between the fluid-structure interaction approach and the finite element method approach to analyze the leaflet flutter in bioprosthetic aortic valve

The low durability of bioprosthetic heart valves (BHV), between 10-15 years, is associated with the development of leaflets flutter. Despite increasing calcification and structural damage of the BHV, leaflets flutter is an understudied condition. Therefore, the objective of this study is compare the oscillation characteristics of BHV leaflets obtained by the finite element method (FEM) technique and by the fluid-structural interaction (FSI) technique. A BHV geometry and a simplified fluid domain were developed. Physiological ventricular and aortic pressure were applied in the FEM and FSI simulations. The BHV were considered with incompressible hyperelastic and isotropic mechanical behavior, while the blood was modeled as a Newtonian fluid. Turbulence was modeled according to the k - omega SST model. The displacement and maximum principal stress results showed that the FSI approach was in better agreement with the in vitro studies in the literature. Furthermore, the leaflet vibration frequency was 12 times lower and the amplitude 50 times higher compared to the FEM method. From the stress distribution in the leaflets, the highest values occurred in the commissure region of the ventricular side for both techniques. In addition, while the stress was more uniform for FEM, FSI showed a stress concentration in the belly region of the leaflets. This study indicates that the use of the FEM technique to assess fatigue intensification due to leaflet fluttering could induce inaccurate conclusions, since it does not incorporate the dynamic fluid impacts on leaflets.