Fluid- and Biomechanical Analysis of Ascending Thoracic Aorta Aneurysm with Concomitant Aortic Insufficiency

Viallon

et al. 2018

Cardiovasc Eng Tech

Purpose. It has been reported clinically that rupture or dissections in thoracic aortic aneurysms (TAA) often occur due to hypertension which may be modelled with sudden increase of peripheral resistance, inducing acute changes of blood volumes in the aorta. There is clinical evidence that more compliant aneurysms are less prone to rupture as they can sustain such changes of volume. The aim of the current paper is to verify this paradigm by evaluating computationally the role played by the variation of peripheral resistance and the impact of aortic stiffness onto peak wall stress in ascending TAA. Methods. Fluid-Structure Interaction (FSI) analyses were performed using patient-specific geometries and boundary conditions derived from 4D MRI datasets acquired on a patient. Blood was assumed incompressible and was treated as a non-Newtonian fluid using the Carreau model while the wall mechanical properties were obtained from the bulge inflation tests carried out in vitro after surgical repair. The Navier Stokes equations were solved in ANSYS Fluent. The Arbitrary Lagrangian Eulerian formulation was used to account for the wall deformations. At the interface between the solid domain and the fluid domain, the fluid pressure was transferred to the wall and the displacement of the wall was transferred to the fluid. The two systems were connected by the System Coupling component which controls the solver execution of fluid and solid simulations in ANSYS. Fluid and solid domains were solved sequentially starting from the fluid simulations. Results. Distributions of blood flow, wall shear stress and wall stress were evaluated in the ascending thoracic aorta using the FSI analyses. We always observed a significant flow eccentricity in the simulations, in very good agreement with velocity profiles measured using 4D MRI. The results also showed significant increase of peak wall stress due to the increase of peripheral resistance and aortic stiffness. In the worst case scenario, the largest peripheral resistance (10 10 kg.s.m -4 ) and stiffness (10 MPa) resulted in a maximal principal stress equal to 702 kPa, whereas it was only 77 kPa in normal conditions. Conclusions. This is the first time that the risk of rupture of an aTAA is quantified in case of the combined effects of hypertension and aortic stiffness increase. Our findings suggest that a stiffer TAA may have the most altered distribution of wall stress and an acute change of peripheral vascular resistance could significantly increase the risk of rupture for a stiffer aneurysm.

Section: Introductionmentioning

confidence: 99%

Evaluation of Peak Wall Stress in an Ascending Thoracic Aortic Aneurysm Using FSI Simulations: Effects of Aortic Stiffness and Peripheral Resistance

Campobasso

Viallon

et al. 2018

Cardiovasc Eng Tech

“…Validated CFD models allow accurate analysis in terms of high temporal and spatial resolution which is particularly important to properly estimate the wall shear stress distribution. On the other hand, 4D flow MRI directly measures in vivo the 3D blood flow velocities independently of boundary conditions (Bürk et al, 2012;Condemi et al 2017).…”

Section: Methodsmentioning

confidence: 99%

“…Three cardiac cycles were simulated. The convergence of the solution was assessed for residual errors below 10 -3 (Condemi et al 2017). After deriving blood flow pathlines at systole from CFD analysis, the following quantities were derived across the ascending thoracic aorta: the flow eccentricity (Floweccentricity, 0 indicates that the flow is centrally distributed with respect to the vessel centerline, and 1 indicates that the flow is eccentric and impinges against the vessel walls), the helicity intensity (h2), the circumferential time averaged wall shear stress (TAWSScircumferential) and the cumulative viscous energy loss at the systolic peak ( ′ ).…”

Section: Methodsmentioning

confidence: 99%

“…This altered hemodynamics has been related to aortopathy through mechanical weakening of the aortic wall. It is also known that patients with dilated ascending thoracic aorta, but with physiologically normal aortic valve, exhibit alterations in 3D aortic blood flow patterns such as enhanced helix or vortex flow, jet flow impingement and increased WSS (Barker et al, 2012;Bürk et al, 2012;Condemi et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Ascending thoracic aorta aneurysm repair induces positive hemodynamic outcomes in a patient with unchanged bicuspid aortic valve

Journal of Biomechanics

Campisi

Viallon

et al. 2018

Self Cite

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“…Aortic aneurysm can be detected with physical examination but needs to be confirmed with a series of medical imaging tests such as ultrasound or computerized tomography (CT) scans . When diagnosed, the best way to reduce the risk of rupture is with prompt surgical intervention, although in some cases complications associated with surgical treatment may be deemed greater than the risk of rupture itself . To decide on the appropriate treatment strategy for each individual patient, it is necessary to obtain a reliable predictor to estimate the state of aneurysm and monitor growth.…”

Section: Introductionmentioning

confidence: 99%

Computational prediction of hemodynamical and biomechanical alterations induced by aneurysm dilatation in patient‐specific ascending thoracic aortas

Jayendiran

Numer Methods Biomed Eng

Campisi

et al. 2020

The aim of the present work is to propose a robust computational framework combining computational fluid dynamics (CFD) and 4D flow MRI to predict the progressive changes in hemodynamics and wall rupture index (RPI) induced by aortic morphological evolutions in patients harboring ascending thoracic aortic aneurysms (ATAAs). An analytical equation has been proposed to predict the aneurysm progression based on age, sex, and body surface area. Parameters such as helicity, wall shear stress (WSS), time‐averaged WSS, oscillatory shear index, relative residence time, and viscosity were evaluated for two patients at different stages of aneurysm growth, and compared with age‐sex‐matched healthy subjects. The study shows that evolution of hemodynamics and RPI, despite being very slow in ATAAs, is strongly affected by morphological alterations and, in turn could impact biomechanical factors and aortic mechanobiology. An aspect of the current work is that the patient‐specific 4D MRI data sets were obtained with a follow‐up of 1 year and the measured time‐averaged velocity maps and flow eccentricity were compared with the CFD simulation for validation. The computational framework presented here is capable of capturing the blood flow patterns and the hemodynamic descriptors during the various stages of aneurysm growth. Further investigations will be conducted in order to verify these results on a larger cohort of patients and with long follow‐up times to finally elucidate the link between deranged hemodynamics, AA geometry, and wall mechanical properties in ATAAs.