Effect of Wall Motion Sampling on CFD-Derived Left Atrial Flow Metrics

The temporal resolution of medical imaging sequences used to drive patient-specific computational fluid dynamics (CFD) simulations remains limited, typically providing 10-20 frames per cardiac cycle. Therefore, temporal interpolation to reconstruct left atrial (LA) wall motion is required, but its impact on hemodynamic predictions has not been systematically characterized. To investigate this, we constructed high-temporal-resolution reference wall motion data using electromechanical (EM) simulations on five patient-specific atrial geometries with a history of atrial fibrillation. We then generated temporally downsampled datasets to emulate clinical frame rates (10, 20, and 40 frames per cycle) and performed CFD simulations to isolate the effects of temporal undersampling on hemodynamic metrics. The focus was placed on kinetic energy, KE, and residence time, TR, particularly in the left atrial appendage (LAA), where thrombosis is most likely to occur. We employed an immersed boundary method to prescribe the wall motion and computed blood TR through a passive scalar transport equation. Results indicate that while global LA hemodynamic indices showed relatively modest sensitivity to frame rate (errors <15%), LAA TR was substantially affected, with 10-frame reconstructions overestimating TR by up to 43% compared to reference values. CFD simulations based on 20 and 40 frames per cycle yielded favorable agreement with reference results (errors ≤9%), whereas 10-frame reconstructions consistently produced elevated stasis metrics and failed to capture physiological features like atrial contraction peaks. Our analysis suggests that anatomical reconstructions with ≥20 frames per cardiac cycle provide sufficiently reliable LAA blood-stasis indices, while lower temporal resolutions should be interpreted cautiously, particularly for patient stratification purposes where accurate ranking is essential.