Subject-Specific Calculation of Left Atrial Appendage Blood-Borne Particle Residence Time Distribution in Atrial Fibrillation

Sanatkhani, Soroosh; Nedios, Sotirios; Menon, Prahlad G.; Bollmann, Andreas; Hindricks, Gerhard; Shroff, Sanjeev G.

doi:10.3389/fphys.2021.633135

Cited by 19 publications

(29 citation statements)

References 25 publications

(59 reference statements)

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“…Multiple studies have established a relationship between LAA blood stasis, spontaneous echocardiographic contrast, and the risk of LAA thrombosis, especially in patients with AF 30,48 . Furthermore, previous CFD analyses of LA hemodynamics consistently report shear rates below 70 s −1 and residence times above 5 s inside the LAA, 27,28,51 which, according to data from in vitro experiments, should cause RBC aggregation. However, there is a lack of studies evaluating the importance of non‐Newtonian blood rheology in the LA and LAA hemodynamics.…”

Section: Discussionmentioning

confidence: 96%

Non‐Newtonian blood rheology impacts left atrial stasis in patient‐specific simulations

Gonzalo

García-Villalba

Rossini

et al. 2022

Numer Methods Biomed Eng

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The lack of mechanically effective contraction of the left atrium (LA) during atrial fibrillation (AF) disturbs blood flow, increasing the risk of thrombosis and ischemic stroke. Thrombosis is most likely in the left atrial appendage (LAA), a small narrow sac where blood is prone to stagnate. Slow flow promotes the formation of erythrocyte aggregates in the LAA, also known as rouleaux, causing viscosity gradients that are usually disregarded in patientspecific simulations. To evaluate these non-Newtonian effects, we built atrial models derived from 4D computed tomography scans of patients and carried out computational fluid dynamics simulations using the Carreau-Yasuda constitutive relation. We examined six patients, three of whom had AF and LAA thrombosis or a history of transient ischemic attacks (TIAs). We modeled the effects of hematocrit and rouleaux formation kinetics by varying the parameterization of the Carreau-Yasuda relation and modulating non-Newtonian viscosity changes based on residence time. Comparing non-Newtonian and Newtonian simulations indicates that slow flow in the LAA increases blood viscosity, altering secondary swirling flows and intensifying blood stasis. While some of these effects are subtle when examined using instantaneous metrics like shear rate or kinetic energy, they are manifested in the blood residence

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Section: Discussionmentioning

confidence: 96%

Non‐Newtonian blood rheology impacts left atrial stasis in patient‐specific simulations

Gonzalo

García-Villalba

Rossini

et al. 2022

Numer Methods Biomed Eng

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“…The LA wall was considered rigid, i.e., without movement, resulting in a pure computational fluid dynamics (CFD) modelling study. Such an assumption is a common approach in the literature [15,18,19,22,23,26,32], which is based on the reduced wall movement in patients with atrial fibrillation.…”

Section: Scenario 1: Constant (Null) Inlet Pressure Imaging-based Per...mentioning

confidence: 99%

“…Qualitative analyses of the blood flow patterns with streamline-based visualisation are commonly included. Arguably, the published investigations are usually based on only a few (<10) sets of patient-specific LA geometries (see Table 1), yet the most recent LA flow simulation studies [27,32,34] propose automatic modelling pipelines that allow substantial improvements in the capacity to process increased numbers of cases. Due to the extensive range of modelling options reported in LA computational fluid dynamics, there is a need for best practice guidelines to build robust models and achieve reliable simulations as regards relevant clinical outcomes in LAAO.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity Analysis of In Silico Fluid Simulations to Predict Thrombus Formation after Left Atrial Appendage Occlusion

et al. 2021

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Atrial fibrillation (AF) is nowadays the most common human arrhythmia and it is considered a marker of an increased risk of embolic stroke. It is known that 99% of AF-related thrombi are generated in the left atrial appendage (LAA), an anatomical structure located within the left atrium (LA). Left atrial appendage occlusion (LAAO) has become a good alternative for nonvalvular AF patients with contraindications to anticoagulants. However, there is a non-negligible number of device-related thrombus (DRT) events, created next to the device surface. In silico fluid simulations can be a powerful tool to better understand the relation between LA anatomy, haemodynamics, and the process of thrombus formation. Despite the increasing literature in LA fluid modelling, a consensus has not been reached yet in the community on the optimal modelling choices and boundary conditions for generating realistic simulations. In this line, we have performed a sensitivity analysis of several boundary conditions scenarios, varying inlet/outlet and LA wall movement configurations, using patient-specific imaging data of six LAAO patients (three of them with DRT at follow-up). Mesh and cardiac cycle convergence were also analysed. The boundary conditions scenario that better predicted DRT cases had echocardiography-based velocities at the mitral valve outlet, a generic pressure wave from an AF patient at the pulmonary vein inlets, and a dynamic mesh approach for LA wall deformation, emphasizing the need for patient-specific data for realistic simulations. The obtained promising results need to be further validated with larger cohorts, ideally with ground truth data, but they already offer unique insights on thrombogenic risk in the left atria.

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“…Multiple studies have established a relationship between LAA blood stasis, spontaneous echocardiographic contrast, and the risk of LAA thrombosis, especially in patients with AF [48, 30]. Furthermore, previous CFD analyses of LA hemodynamics consistently report shear rates below 70 s −1 and residence times above 5 s inside the LAA [27, 28, 51], which, according to data from in vitro experiments, should cause RBC aggregation. However, there is a lack of studies evaluating the importance of non-Newtonian blood rheology in the LA and LAA hemodynamics.…”

Section: Discussionmentioning

confidence: 99%

Section: Red Blood Cell Aggregation In the La And Laamentioning

confidence: 97%

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

Gonzalo

García-Villalba

Rossini³

et al. 2021

Preprint

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Atrial fibrillation (AF) is the most common arrhythmia, affecting ~35M people worldwide. The irregular beating of the left atrial (LA) caused by AF impacts the LA hemodynamics increasing the risk of thrombosis and ischemic stroke. Most LA thrombi appear in its appendage (LAA), a narrow sac of varied morphology where blood is prone to stagnate. In the LAA, the combination of slow blood flow and low shear rates (<100 [1/s]) promotes the formation of red blood cell aggregations called rouleaux. Blood experiences a non-Newtonian behavior when rouleaux formed that has not been considered in previous CFD analysis of the LA. We model the anatomy and motion of the LA from 4D-CT images and solve the blood flow inside the LA geometry with our CFD in-house code, which models Non-Newtonian rheology with the shear-hematocrit-dependent Carreau-Yasuda equation. We cover a wide range of non-Newtonian effects considering a small and a large hematocrit, including an additional constitutive relation to account for themrouleaux formation time, and we compare our results with Newtonian simulations. Blood rheology influence in LAA hemostasis is studied in 6 patient-specific anatomies. Two subjects had an LAA thrombus (digitally removed before running the simulations), another had a history of TIAs, and the remaining three had normal atrial function. In our simulations, the shear rate remains below 50 [1/s] in the LAA for all non-Newtonian models considered. This triggers an increase of viscosity that alters the flow behavior in that site, which exhibits different flow patterns than Newtonian simulations. These hemodynamic changes translate into differences in the LAA hemostasis, calculated with the residence time.

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Subject-Specific Calculation of Left Atrial Appendage Blood-Borne Particle Residence Time Distribution in Atrial Fibrillation

Cited by 19 publications

References 25 publications

Non‐Newtonian blood rheology impacts left atrial stasis in patient‐specific simulations

Non‐Newtonian blood rheology impacts left atrial stasis in patient‐specific simulations

Sensitivity Analysis of In Silico Fluid Simulations to Predict Thrombus Formation after Left Atrial Appendage Occlusion

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

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