Quantifying the Functional Effect of Transmural Interpolation Strategies on Atrial Wave Propagation Using a Custom...

Atrial fibrillation (AF) management increasingly relies on patient-specific computational modeling to simulate arrhythmia mechanisms and optimize ablation strategies. However, predictive reliability is strongly influenced by accurate reconstruction of myocardial fiber architecture, which governs electrical anisotropy. Because patient-specific atrial fiber orientations cannot currently be acquired reliably in vivo using diffusion tensor magnetic resonance imaging (DT-MRI), alternative computational mapping strategies are required. This protocol presents a comprehensive, open-source pipeline for constructing patient-specific 3D models of the human left atrium with explicit transmural fiber reconstruction from high-resolution clinical computed tomography (CT) data. The methodology extends the Universal Atrial Coordinate (UAC) framework into the volumetric domain by solving the Laplace-Dirichlet problem to derive a continuous transmural coordinate. This enables transfer of atlas-based fiber orientations and subsequent interpolation across the atrial wall. Linear and threshold-based transmural interpolation strategies are quantitatively compared, and their effects on fiber orientation and macroscopic wavefront propagation are evaluated. Across all six models, the mean angular deviation between interpolation methods was 8.06 ± 1.13°. Electrophysiological simulations demonstrate that the choice of interpolation delayed activation in Region 1 by 2.0 ± 0.6 ms, corresponding to 6.1 ± 1.5 ms (p = 0.031 for both comparisons). The open-source pipeline and patient-specific CT-based atrial models provide a reproducible framework for evaluating the functional effects of transmural fiber reconstruction strategies.