On the Modeling of Left Atrial Appendage Inversion: a Reverse Growth Analysis

Atrial fibrillation (AF) can lead to thromboembolic events due to an increased propensity for clot formation in the left atrial appendage (LAA). Current methods for reducing the risk of these events, such as surgical exclusion and percutaneous occlusion, have limitations that restrict their applicability and efficacy. Sulkin et al. [1] previously demonstrated the clinical feasibility of a novel procedure involving partial inversion of the LAA to occlude the atrium appendage. This study aimed to explore left atrial appendage inversion (LAAI) on four patient-specific LAA morphologies, each representing a distinct morphological variant: chicken wing, cactus, windsock, and cauliflower. Left atrial geometries were extracted from CT images and then used as input for patient-specific finite element analysis simulations of LAAI. The latter was simulated by pulling the elements at the LAA tip along a predefined path to mimic the inversion. The deformed configuration was then analyzed to map the stress field and establish a stressresorption relationship. Folded LAA wall results in a transition from tensile to compressive stress distribution, which can induce tissue resorption in the inverted appendage. This compressive stress distribution is linked to the stretch distribution (λ) generated in the folded LAA. To define a stress-resorption relationship, the growth and reverse growth kinematics proposed by Lee et al. [2] was adopted. This approach involves a reversible growth multiplier (θ) that represents the combined effects of elastic deformation and tissue growth/reverse growth., The trend of θ based on the straindriven growth model was derived using the Ogden constitutive model. The value of θ depended to λ, and tissue resorption was triggered beyond a stretch threshold. Thus, we concluded that λ generated in the LAAI region acts as a remodeling stimulator. This occurred until λ decrease below a minimum value and θ converged to a final value following an exponential decay trend. Our findings resulted in a stress-growth model, applied in four LAA morphologies, that can model tissue resorption over time as compressive tensile gradually relax in the inverted LAA.