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Research Papers

Hemodynamic Profile of Two Aortic Endografts Accounting for Their Postimplantation Position

[+] Author and Article Information
Anastasios Raptis

Cardiovascular Surgery Department,
Sector of Surgery,
Faculty of Medicine,
School of Health Sciences,
University of Ioannina,
Ioannina 45500, Greece;
Laboratory for Vascular Simulations,
Institute of Vascular Diseases,
Ioannina 45500, Greece
e-mails: anraptis@cc.uoi.gr; raptistasos@gmail.com

Michalis Xenos

Department of Mathematics,
University of Ioannina,
Ioannina 45500, Greece;
Laboratory for Vascular Simulations,
Institute of Vascular Diseases,
Ioannina 45500, Greece
e-mail: mxenos@cc.uoi.gr

Efstratios Georgakarakos

Department of Vascular Surgery,
“Democritus” Medical School,
University Hospital of Alexandroupolis,
Alexandroupolis 68100, Greece
e-mail: efstratiosgeorg@gmail.com

George Kouvelos

Department of Vascular Surgery,
Faculty of Medicine,
University of Thessaly,
Larissa 41334, Greece
e-mail: geokouv@gmail.com

Athanasios Giannoukas

Department of Vascular Surgery,
Faculty of Medicine,
University of Thessaly,
Larissa 41334, Greece;
Laboratory for Vascular Simulations,
Institute of Vascular Diseases,
Ioannina 45500, Greece
e-mail: giannouk@med.uth.gr

Miltiadis Matsagkas

Department of Vascular Surgery,
Faculty of Medicine,
University of Thessaly,
Larissa 41334, Greece;
Laboratory for Vascular Simulations,
Institute of Vascular Diseases,
Ioannina 45500, Greece
e-mails: mimats@med.uth.gr; mmats@otenet.gr

1Corresponding author.

Manuscript received June 24, 2016; final manuscript received December 22, 2016; published online May 3, 2017. Assoc. Editor: Marc Horner.

J. Med. Devices 11(2), 021003 (May 03, 2017) (8 pages) Paper No: MED-16-1247; doi: 10.1115/1.4035687 History: Received June 24, 2016; Revised December 22, 2016

Endovascular aneurysm repair (EVAR) is a clinically effective technique for treating anatomically eligible abdominal aortic aneurysms (AAAs), involving the deployment of an endograft (EG) that is designed to prevent blood leakage in the aneurysmal sac. While most EGs have equivalent operating principles, the hemodynamic environment established by different EGs is not necessarily the same. So, to unveil the post-EVAR hemodynamic properties, we need an EG-specific computational approach that currently lacks from the literature. Endurant and Excluder are two EGs with similar pre-installation designs. We assumed that the flow conditions in the particular EGs do not vary significantly. The hypothesis was tested combining image reconstructions, computational fluid dynamics (CFD), and statistics, taking into account the postimplantation position of the EGs. Ten patients with Endurant EGs and ten patients with Excluder EGs were included in this study. The two groups were matched with respect to the preoperative morphological characteristics of the AAAs. The EG models are derived from image reconstructions of postoperative computed tomography scans. Wall shear stress (WSS), displacement force, velocity, and helicity were calculated in regions of interest within the EG structures, i.e., the main body, the upper and lower part of the limbs. Excluder generated higher WSS compared to Endurant, especially on the lower part of the limbs (p = 0.001). Spatial fluctuations of WSS were observed on the upper part of the Excluder limbs. Higher blood velocity was induced by Excluder in all the regions of interest (p = 0.04, p = 0.01, and p = 0.004). Focal points of secondary flow were detected in the main body of Endurant and the limbs of Excluder. The displacement force acting on the lower part of the Excluder limbs was stronger compared to the Endurant one (p = 0.03). The results showed that two similar EGs implanted in similar AAAs can induce significantly different flow properties. The delineation of the hemodynamic features associated with the various commercially available EGs could further promote the personalization of treatment offered to aneurysmal patients and inspire ideas for the improvement of EG designs in the future.

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Figures

Grahic Jump Location
Fig. 1

Schematic definition of the ROI. Part of the main body, 3 cm above the bifurcation, the upper part of the limbs, 4 cm below the bifurcation, and lower part of the limbs, 4 cm above the distal end of the EG. Diagrams of pulse pressure and flow rate conditions are applied at theinlet and the outlets, respectively.

Grahic Jump Location
Fig. 2

The mean value and standard error of (a) maximum WSS, (b) maximum velocity, (c) mean helicity, and (d) displacement forces in all the ROI. (e) Displacement forces at indicative time instances throughout the cardiac cycle at the lower part of the limbs. The asterisk indicates statistical significance (p < 0.05).

Grahic Jump Location
Fig. 3

WSS spatial distribution at peak systole for representative Endurant and Excluder cases. The two charts below depict the linear approximation of average maximum WSS and velocity with respect to the ROI.

Grahic Jump Location
Fig. 4

Focal points of secondary flow at mid-diastole for representative Endurant and Excluder cases. In the left boxes for each group, the visualization of the component of velocity in the x direction. In the right boxes for each group, the visualization of the component of velocity in the y direction. Intense secondary flow in the main body of Endurant and the limbs of Excluder.

Grahic Jump Location
Fig. 5

Contours of velocity magnitude and surface streamlines on a plane for an Endurant and an Excluder case. At peak systole, blood flow is streamlined for both cases. At mid-diastole, a larger recirculation zone, followed by smaller ones after the flow divider, was observed for the Endurant case. A more confined recirculation is developing in the main body of the Excluder case, but the flow is streamlined in the entrance of the limbs after the bifurcation. Recirculation zone is again observed lower at the limbs.

Grahic Jump Location
Fig. 6

Evolution of helical structures throughout the cardiac cycle for representative Endurant and Excluder cases. Formation of helical structures during the deceleration phase and propagation during diastole.

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