Stroke is strongly associated with atrial dysfunction, such as atrial fibrillation, with the left atrial appendage (LAA) being a major site of thrombus formation due to its irregular, pouch-like and trabeculated structure. However, experimental data remain scarce, and its structural heterogeneity challenges standard biomechanical characterization approaches. This study combines 3D thickness mapping, uniaxial testing, and modeling to investigate how trabeculae contribute to apparent anisotropy.
Two rectangular specimens were excised from each of 40 porcine atrial appendage free walls. One was tested in the longitudinal direction (with respect to trabeculae) and the other in the transverse direction under uniaxial loading. Dimensions were measured with a caliper and complemented by high-resolution 3D optical scans, enabling full-field thickness mapping. Finite element inverse identification using an isotropic hyperelastic Veronda–Westmann model was implemented and compared to standard analytical identification. Parameters identified in the longitudinal direction were then used in the FE model of the transverse sample. Simulation results were compared to experimental data using RMSE.
Thickness maps revealed substantial intra- and inter-sample variability. All specimens exhibited nonlinear behavior, with parameters strongly dependent on loading direction. The finite element inverse approach, incorporating accurate sample geometry, significantly reduced prediction errors compared to the analytical method (p < 0.03) for the transverse response. These findings suggest that tissue macrostructure partly explains the observed anisotropy, although residual discrepancies indicate other contributing mechanisms.
These results demonstrate that trabeculae strongly influence atrial appendage passive mechanics and contribute to apparent anisotropy. Residual discrepancies between FE predictions and experimental measurements suggest additional contributions from meso- and microstructural features, such as cardiomyocyte orientation and layered organization. Preliminary micro-CT imaging supports this interpretation, revealing abrupt structural transitions. Overall, these findings highlight the importance of incorporating trabecular geometry and structural heterogeneity into models to accurately capture the mechanical behavior of heterogeneous cardiac tissues.