Demonstration of Patient-Specific Simulations to Assess Left Atrial Appendage Thrombogenesis Risk

Abstract

Atrial fibrillation (AF) alters left atrial (LA) hemodynamics, which can lead to thrombosis in the left atrial appendage (LAA), systemic embolism and stroke. A personalized risk-stratification of AF patients for stroke would permit improved balancing of preventive anticoagulation therapies against bleeding risk. We investigated how LA anatomy and function impact LA and LAA hemodynamics, and explored whether patient-specific analysis by computational fluid dynamics (CFD) can predict the risk of LAA thrombosis. We analyzed 4D-CT acquisitions of LA wall motion with an in-house immersed-boundary CFD solver. We considered six patients with diverse atrial function, three with either a LAA thrombus (removed digitally before running the simulations) or a history of transient ischemic attacks (LAAT/TIA-pos), and three without a LAA thrombus or TIA (LAAT/TIA-neg). We found that blood inside the left atrial appendage of LAAT/TIA-pos patients had marked alterations in residence time and kinetic energy when compared with LAAT/TIA-neg patients. In addition, we showed how the LA conduit, reservoir and booster functions distinctly affect LA and LAA hemodynamics. Finally, fixed-wall and moving-wall simulations produced different LA hemodynamics and residence time predictions for each patient. Consequently, fixed-wall simulations risk-stratified our small cohort for LAA thrombosis worse than moving-wall simulations, particularly patients with intermediate LAA residence time. Overall, these results suggest that both wall kinetics and LAA morphology contribute to LAA blood stasis and thrombosis.

Presence of Left Atrial Fibrosis May Contribute to Aberrant Hemodynamics and Increased Risk of Stroke in Atrial Fibrillation Patients

“…This suggests that neglecting LA wall motion in CFD simulations might not produce accurate hemodynamics. These results are in accordance with the findings of Garcia-Villalba et al, who demonstrated that simulations with no LA wall motion results in different flow fields as compared to simulations with moving LA walls ( Garcia-Villalba et al, 2021 ). However, our LA wall motion method is based on volume-based interpolation, which might not be representative of the physiological LA wall motion for these patients, which could be a possible reason for modest correlation coefficient.…”

“…CFD studies have shown that LA hemodynamics is highly dependent on incorporating the LA wall motion in the simulations ( Koizumi et al, 2015 ; Garcia-Villalba et al, 2021 ). To investigate the effect of LA wall motion in our study, we performed simulations for all our models with LA wall assumed as rigid non-moving wall ( Supplementary Material ).…”

Non-Newtonian Blood Rheology Impacts Left Atrial Stasis in Patient-Specific Simulations

“…We retrospectively considered the N = 6 left atrial models of García-Villalba et al [35], consisting of 4D (3D, time-resolved) patient-specific segmentations of human left atria obtained from computed tomography (CT) imaging. Three patients had normal LA volume and function, were imaged in sinus rhythm, and did not have a left atrial appendage (LAA) thrombus.…”

“…Some of these simulations include models of heart valve motion [22,26,15,17,27,28,29] and some can resolve the intricate domain surface caused by endocardial trabeculation [28,29]. Motivated by the need for patient-specific prediction of LAA blood stasis, the number of CFD simulations of LA flow is growing rapidly [30,31,32,33,34,35].…”

“…The present study evaluates whether blood's shear-thinning rheology significantly affects CFD estimations of LAA blood stasis. To this end, we carried out numerical simulations of left atrial flow considering a Carreau-Yasuda constitutive relation, and compared the results with those from Newtonian simulations [35]. We examined N = 6 patients with covering a wide range of atrial morphology and function, three of whom had LAA thrombosis or a history of transient ischemic attacks (TIAs).…”