Computational Fluid Dynamics Study of Cerebral Thromboembolism Risk in Ventricular Assist Device Patients: Effects of Pulsatility and Thrombus Origin

2021 ◽  
Author(s):  
Ray Prather ◽  
Eduardo Divo ◽  
Alain J. Kassab ◽  
William DeCampli
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Unsteady Flow ◽  
Aortic Root ◽  
Flow Analysis ◽  
Patient Specific ◽  
Assist Device ◽  
Device Placement ◽  
Cardiovascular Simulation ◽  
Outflow Graft

Abstract Purpose: This study investigates the hypothesis that by surgically manipulating the outflow graft implantation during ventricle assist device placement, it may be possible to reduce the risk of cerebral embolism. Methods: We investigate this hypothesis using a computational approach on a patient specific basis under fully-pulsatile hemodynamics with a multi-scale computational fluid dynamics model incorporating a coupled Eulerian-Lagrangian scheme that effectively tracks emboli in the fluid domain. Blood is modeled as a non-Newtonian fluid based on the hematocrit level. Results: Preliminary flow analysis shows that, depending on the anastomosis angle the LVAD can enhance the flow to the cerebral circulation by nearly 31%. Z-test results suggest that unsteady flow modelling ought to be an integral part of any cardiovascular simulation with residual ventricular function. Assuming unsteady flow conditions, a shallow LVAD outflow graft anastomosis angle is the most optimal if thrombi are released from the aortic root reducing cerebral embolization incidence to 15.5% and from the ventricle to 17%, while a more pronounced anastomosis angle becomes advantageous when particles originate from the LVAD with an embolization rate of 16.9%. Conclusion: Overall, computations suggest that a pronounced LVAD anastomosis angle is the better implementation. Unsteady modeling is shown to be necessary in the presence of significant antegrade aortic root flow which induces cyclical flow patterns due to residual pulsatility. On the other hand depending on thrombus origin and VAD anastomosis angle there is a strong tradeoff in embolization rates.

Patient-specific computational fluid dynamics analysis of transcatheter aortic root replacement with chimney coronary grafts

2020 ◽  
Author(s):  
Michele Conti ◽  
Rodrigo M Romarowski ◽  
Anna Ferrarini ◽  
Matteo Stochino ◽  
Ferdinando Auricchio ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Drop ◽  
Aortic Root ◽  
Coronary Circulation ◽  
Ascending Aorta ◽  
Patient Specific ◽  
Coronary Perfusion ◽  
Computational Fluid Dynamics Analysis ◽  
The Impact

Abstract OBJECTIVES Transcatheter aortic root repair (TARR) consists of the simultaneous endovascular replacement of the aortic valve, the root and the proximal ascending aorta. The aim of the study is to set-up a computational model of TARR to explore the impact of the endovascular procedure on the coronary circulation supported by chimney grafts. METHODS Computed tomography of a patient with dilated ascending aorta was segmented to obtain a 3-dimensional representation of the proximal thoracic aorta, including aortic root and supra-aortic branches. Computed assisted design tools were used to modify the geometry to create the post-procedural TARR configuration featuring the main aortic endograft integrated with 2 chimney grafts for coronary circulation. Computational Fluid Dynamics simulations were run in both pre- and post-procedural configurations using a pulsatile inflow and lumped parameter models at the outflows to simulate peripheral aortic and coronary circulation. Differences in coronary flow and pressure along the cardiac cycle were evaluated. RESULTS After the virtual implant of the TARR device with coronary grafts, the flow became more organized and less recirculation was seen in the ascending aorta. Coronary perfusion was guaranteed with negligible flow differences between pre- and post-procedural configurations. However, despite being well perfused by chimney grafts, the procedure induces an increase of the pressure drop between the coronary ostia and the ascending aorta of 8 mmHg. CONCLUSIONS The proposed numerical simulations, in the specific case under investigation, suggest that the TARR technique maintains coronary perfusion through the chimney grafts. This study calls for experimental validation and further analyses of the impact of TARR on cardiac afterload, decrease of aortic compliance and local pressure drop induced by the coronary chimney grafts.

Patient-Specific Computational Fluid Dynamics Reveal Localized Flow Patterns Predictive of Post–Left Ventricular Assist Device Aortic Incompetence

2021 ◽  
Author(s):  
Rohan Shad ◽  
Alexander D. Kaiser ◽  
Sandra Kong ◽  
Robyn Fong ◽  
Nicolas Quach ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Left Ventricular Assist Device ◽  
Ventricular Assist Device ◽  
Aortic Root ◽  
Left Ventricular ◽  
Oscillatory Shear Index ◽  
Assist Device ◽  
Ventricular Assist ◽  
Left Ventricular Assist

Background: Progressive aortic valve disease has remained a persistent cause of concern in patients with left ventricular assist devices. Aortic incompetence (AI) is a known predictor of both mortality and readmissions in this patient population and remains a challenging clinical problem. Methods: Ten left ventricular assist device patients with de novo aortic regurgitation and 19 control left ventricular assist device patients were identified. Three-dimensional models of patients’ aortas were created from their computed tomography scans, following which large-scale patient-specific computational fluid dynamics simulations were performed with physiologically accurate boundary conditions using the SimVascular flow solver. Results: The spatial distributions of time-averaged wall shear stress and oscillatory shear index show no significant differences in the aortic root in patients with and without AI (mean difference, 0.67 dyne/cm 2 [95% CI, −0.51 to 1.85]; P =0.23). Oscillatory shear index was also not significantly different between both groups of patients (mean difference, 0.03 [95% CI, −0.07 to 0.019]; P =0.22). The localized wall shear stress on the leaflet tips was significantly higher in the AI group than the non-AI group (1.62 versus 1.35 dyne/cm 2 ; mean difference [95% CI, 0.15–0.39]; P <0.001), whereas oscillatory shear index was not significantly different between both groups (95% CI, −0.009 to 0.001; P =0.17). Conclusions: Computational fluid dynamics serves a unique role in studying the hemodynamic features in left ventricular assist device patients where 4-dimensional magnetic resonance imaging remains unfeasible. Contrary to the widely accepted notions of highly disturbed flow, in this study, we demonstrate that the aortic root is a region of relatively stagnant flow. We further identified localized hemodynamic features in the aortic root that challenge our understanding of how AI develops in this patient population.

scholarly journals Morphological and Hemodynamic Changes during Cerebral Aneurysm Growth

2021 ◽  
Vol 11 (4) ◽  
pp. 520
Author(s):  
Emily R. Nordahl ◽  
Susheil Uthamaraj ◽  
Kendall D. Dennis ◽  
Alena Sejkorová ◽  
Aleš Hejčl ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Swirling Flow ◽  
Morphological Changes ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Aneurysm Wall ◽  
Aneurysm Growth ◽  
Computational Fluid Dynamics Cfd

Computational fluid dynamics (CFD) has grown as a tool to help understand the hemodynamic properties related to the rupture of cerebral aneurysms. Few of these studies deal specifically with aneurysm growth and most only use a single time instance within the aneurysm growth history. The present retrospective study investigated four patient-specific aneurysms, once at initial diagnosis and then at follow-up, to analyze hemodynamic and morphological changes. Aneurysm geometries were segmented via the medical image processing software Mimics. The geometries were meshed and a computational fluid dynamics (CFD) analysis was performed using ANSYS. Results showed that major geometry bulk growth occurred in areas of low wall shear stress (WSS). Wall shape remodeling near neck impingement regions occurred in areas with large gradients of WSS and oscillatory shear index. This study found that growth occurred in areas where low WSS was accompanied by high velocity gradients between the aneurysm wall and large swirling flow structures. A new finding was that all cases showed an increase in kinetic energy from the first time point to the second, and this change in kinetic energy seems correlated to the change in aneurysm volume.

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