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Research Papers

Computational Fluid Dynamics Evaluation of the Cross-Limb Stent Graft Configuration for Endovascular Aneurysm Repair

[+] Author and Article Information
Tina L. T. Shek

Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
Toronto, ON, M5S 3G8, Canada

Leonard W. Tse

Division of Vascular Surgery,
Toronto General Hospital, PMCC, UHN,
Toronto, ON, M5G 2C4, Canada

Aydin Nabovati

Department of Mechanical and Industrial Engineering,
Toronto, ON, M5S 3G8, Canada
e-mail: a.nabovati@utoronto.ca

Cristina H. Amon

Institute of Biomaterials and Biomedical Engineering,
Department of Mechanical and Industrial Engineering,
University of Toronto,
Toronto, ON, M5S 3G8, Canada

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received March 14, 2012; final manuscript received October 12, 2012; accepted manuscript posted October 25, 2012; published online November 27, 2012. Assoc. Editor: Hai-Chao Han.

J Biomech Eng 134(12), 121002 (Nov 27, 2012) (9 pages) doi:10.1115/1.4007950 History: Received March 14, 2012; Revised October 12, 2012; Accepted October 25, 2012

The technique of crossing the limbs of bifurcated modular stent grafts for endovascular aneurysm repair (EVAR) is often employed in the face of splayed aortic bifurcations to facilitate cannulation and prevent device kinking. However, little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Previous computational fluid dynamics studies of conventional EVAR grafts have mostly utilized simplified planar stent graft geometries. We herein examined the differences between conventional and cross-limb EVAR by comparing their hemodynamic flow fields (i.e., in the “direct” and “cross” configurations, respectively). We also added a “planar” configuration, which is commonly found in the literature, to identify how well this configuration compares to out-of-plane stent graft configurations from a hemodynamic perspective. A representative patient’s cross-limb stent graft geometry was segmented using computed tomography imaging in Mimics software. The cross-limb graft geometry was used to build its direct and planar counterparts in SolidWorks. Physiologic velocity and mass flow boundary conditions and blood properties were implemented for steady-state and pulsatile transient simulations in ANSYS CFX. Displacement forces, wall shear stress (WSS), and oscillatory shear index (OSI) were all comparable between the direct and cross configurations, whereas the planar geometry yielded very different predictions of hemodynamics compared to the out-of-plane stent graft configurations, particularly for displacement forces. This single-patient study suggests that the short-term hemodynamics involved in crossing the limbs is as safe as conventional EVAR. Higher helicity and improved WSS distribution of the cross-limb configuration suggest improved flow-related thrombosis resistance in the short term. However, there may be long-term fatigue implications to stent graft use in the cross configuration when compared to the direct configuration.

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Figures

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Fig. 1

Computed tomography (CT) image of the representative cross-limb EVAR patient

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Fig. 2

Side view of the idealized (a) direct, (b) cross, and (c) planar stent graft configurations constructed in SolidWorks. Orientations: superior (S), inferior (I), posterior (P), and anterior (A).

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Fig. 3

Predicted total and directional displacement forces for the three graft configurations in steady-state conditions

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Fig. 4

Steady-state streamline projections superimposed on velocity contours at the left iliac artery graft outlet of the direct, cross, and planar graft configurations.

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Fig. 5

Steady-state streamline projections superimposed on velocity contours at the right iliac artery graft outlet of the direct, cross, and planar graft configurations

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Fig. 6

Total displacement force through one cardiac cycle predicted for the three graft configurations

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Fig. 7

Streamline projections superimposed on velocity contours at the left iliac artery graft outlet of the direct, cross, and planar configurations in late systole (t=0.39 s)

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Fig. 8

Streamline projections superimposed on velocity contours at the right iliac artery graft outlet of the direct, cross, and planar configurations in late systole (t=0.39 s)

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Fig. 9

Absolute area-averaged helicity in the (a) left and (b) right CIA graft outlets of the three graft configurations. Peak helicity lagged behind peak systole of the inlet velocity profile.

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Fig. 10

Three-dimensional streamlines within the (a) direct, (b) cross, and (c) planar graft configurations. A dense recirculation zone is prominent in all the graft main bodies (t=0.50 s).

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Fig. 11

Transient area-averaged wall shear stress (AAWSS) comparison between the three graft configurations

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Fig. 12

Fluctuations in transient displacement force components of the three graft configurations

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Fig. 13

Normalized directional force contributions to the time-averaged total displacement force in the three graft configurations

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