Selection of Bifurcated Grafts’ Dimensions during Aorto-Iliac Vascular Reconstruction Based on Their Hemodynamic Performance (original) (raw)
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Impact of aortic grafts on hemodynamics: A 1D computational assessment
2011
Objective: Vascular prostheses currently used in vascular surgery do not have the same mechanical properties as human arteries. This computational study analyses the mechanisms by which grafts, placed in the ascending aorta (proximal) and descending aorta (distal), affect arterial blood pressure. Methods: A one-dimensional cardiovascular model was developed and adapted to include the graft geometry with in vitro measured mechanical properties. Pressure at the aortic root and haemodynamic parameters were computed and compared for a control, proximal and distal graft case. Results: In comparison to the control case, the proximal graft increased characteristic impedance by 58% versus only 1% change for the distal graft. The proximal and distal graft increased pulse pressure by 21% and 10%, respectively. Conclusions: The mechanisms underlying pulse pressure increase are different for proximal and distal grafts. For the proximal graft, the primary reason for pulse pressure rise is augmentation of the forward wave, resulting from characteristic impedance increase. For the distal graft, the pulse pressure rise is associated with augmented wave reflections resulting from compliance mismatch. Overall, the proximal aortic graft resulted in greater haemodynamic alterations than the distal graft. Thus, it is likely that patients who receive ascending aorta grafts are more prone to systolic hypertension and therefore deserve closer blood pressure monitoring. ª
Biomedical Papers, 2013
Objective. Abnormal haemodynamics is commonly agreed to be a major contributor to the development of distal anastomotic intimal hyperplasia. A new vascular graft design proposed by computational studies was used to demonstrate its surgical feasibility and to compare it with the conventional graft in a porcine model. Method. The device was used in 12 eight-month-old pigs, six received the new graft and six had a conventional graft. The proximal graft end was implanted into the aorta, the distal graft end was implanted into the iliac artery. The host artery was ligated in order to simulate occlusion. At 20 weeks after surgery the pigs were killed and the device was excised for histological and morphometric analysis. Results. In five experimental grafts the reconstruction was occluded due to thrombosis; only one prosthesis was patent showing a minimum of neointimal hyperplasia. In the control group too only three of the six grafts were patent. A histological analysis revealed, as the cause of occlusion, fibrous tissue overgrowth corresponding in structure to neointimal hyperplasia. Differences in the number of obliterations and in occlusion rates between the profiles of the two groups were evaluated using the median test (P<0.05). The results were not statistically significant. Conclusion. Although mathematical modelling had shown significant haemodynamic benefits of a naturally bifurcated graft, our study did not confirm its superiority over conventionally used prostheses.
Cardiovascular and interventional radiology, 2014
Endovascular aneurysm repair (EVAR) is considered to be the treatment of choice for abdominal aortic aneurysms (AAA). Despite the initial technical success, EVAR is amenable to early and late complications, among which the migration of the endograft (EG) with subsequent proximal endoleak (Type Ia) leads to repressurization of the AAA sac, exposure to excessive wall stress, and, hence, to potential rupture. This article discusses the influence that certain geometrical factors, such as neck angulation, iliac bifurcation, EG curvature, neck-to-iliac diameter, and length ratios, as well as iliac limbs configuration can exert on the hemodynamic behavior of the EGs. The information provided could help both clinicians and EG manufacturers towards further development and improvement of EG designs and better operational planning.
Numerical analysis of blood flow distribution in 4- and 3-branch vascular grafts
Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs, 2013
Trifurcated arch grafts (3-branch grafts) are now being used to repair the thoracic aorta in addition to conventional arch grafts (4-branch grafts). The anatomical shape of the 3-branch graft is different from the original vessel, so it is necessary for clinical application to evaluate blood flow distribution in the graft to assess whether there is adequate blood flow to the target organs. To achieve this, we developed a computational fluid dynamics (CFD) method to evaluate blood flow distribution in the grafts. Aortic blood flow was measured by phase-contrast magnetic resonance imaging (PC-MRI), and flow distribution into the branched vessels was obtained. The MRI image was used to create a patient-specific image model that represents the geometry of the aortic arch. The CFD analysis method was employed to determine a boundary condition of the blood flow analysis in the aorta using a patient-specific image model. We also created simplified models of 4-branch and 3-branch grafts and...
Hemodynamic Profile of Two Aortic Endografts Accounting for Their Postimplantation Position
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 ¼ 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 ¼ 0.04, p ¼ 0.01, and p ¼ 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 ¼ 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.
Journal of Endovascular Therapy, 2013
urpose: To compare the hemodynamic behavior between an aortic endograft model in the ''crossed-limbs'' configuration and the customary bifurcated deployment position under the influence of several geometric factors. Methods: A crossed-limbs graft and its analogue model with uncrossed limbs were computationally reconstructed. The displacement forces acting over the entire endograft and at the bifurcation and iliac sites separately were calculated using a fluid structure interaction simulation under a range of specific geometric characteristics, namely, the lateral and anteroposterior (AP) neck angulation, the iliac bifurcation angulation, and the endograft curvature. Results: The variations of lateral neck angulation caused a constantly higher total displacement force for the crossed-limbs graft, whereas the force at the bifurcation of the two configurations differed only within a narrow range of 308 to 508. On the contrary, the displacement force at the iliac site was higher in the crossed-limbs configuration only with lateral neck angulation .508, reaching its highest value at 708. The variations of AP neck angulation also caused higher total displacement forces in the crossed-limbs graft. Increasing AP neck angulation values caused generally lower forces at the crossed iliac limbs and higher at its bifurcation, respectively, compared to the uncrossed limbs model. Similarly, the influence of high iliac bifurcation angulation and endograft curvature was associated with slightly elevated forces over the entire crossed-limbs graft and its bifurcation, whereas the opposite held true at the iliac site. Conclusion: Apart from minor differentiations due to geometric alterations, the customary bifurcated and crossed-limbs endografts present similar hemodynamic performance. Further clinical studies should be conducted to confirm the clinical applicability of these findings.
International journal for numerical methods in biomedical engineering, 2013
Endovascular repair is now a recognised procedure for treating abdominal aortic aneurysms. However, post-operative complications such as stent graft migration and thrombus may still occur. To assess these complications numerically, the correct input boundary conditions, which include the full human aorta with associated branching, should be included. Four patient-specific computed tomography scanned bifurcated stent grafts (SGs) were modelled and attached onto a full human aorta, which included the ascending, aortic arch and descending aortas. Two of the SG geometries had a twisted leg configuration, while the other two had conventional nontwisted leg configurations. Computational fluid dynamics was completed for both geometries and the hemodynamics assessed. The complexity of the flow patterns and secondary flows were influenced by the inclusion of the full human aorta at the SG proximal section. During the decelerating phase significant recirculations occurred along the main body ...
Impact of Aortic Grafts on Arterial Pressure: A Computational Fluid Dynamics Study
2011
OBJECTIVE: Vascular prostheses currently used in vascular surgery do not have the same mechanical properties as human arteries. This computational study analyses the mechanisms by which grafts, placed in the ascending aorta (proximal) and descending aorta (distal), affect arterial blood pressure. METHODS: A one-dimensional cardiovascular model was developed and adapted to include the graft geometry with in vitro measured mechanical properties.
Vascular reconstruction: CFD predictions of bypass graft haemodynamics
WIT Transactions on State-of-the-art in Science and Engineering, 2008
Anastomotic intimal hyperplasia is a major cause of failure of arterial bypass grafts. The focal nature of this disease suggests that its development is infl uenced by local haemodynamics. Numerical simulations of pulsatile, non-Newtonian blood fl ow through typical human femorodistal bypass models were performed in order to improve understanding of bypass fl ows and identify any associations between the fl ow features and the sites most susceptible to the disease. In general, the fl ow at the distal anastomosis is characterised by extensive recirculation, fl ow separation and reversal, complicated three-dimensional fl ow paths and an unusual wall shear stress distribution. It is concluded that progression of intimal hyperplasia will be encouraged by elevated fl uid particle residence times and adverse shear stresses in the vicinity of the junction. A notable dependence of the fl ow patterns on aspects of the bypass geometry, including the graft attachment angle and the ratio of the...
Journal of Endovascular Therapy, 2012
To evaluate the displacement forces acting on an aortic endograft when the iliac limbs are crossed (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;ballerina&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; position). An endograft model was computationally reconstructed based on data from a patient whose infrarenal aortic aneurysm had an endovascular stent-graft implanted with the iliac limbs crossed. Computational fluid dynamics analysis determined the maximum displacement force on the endograft and separately on the bifurcation and iliac limbs. Its analogue model was reconstructed for comparison, assuming the neck, main body, and total length constant but considering the iliac limbs to be deployed in the usual bifurcated mode. Calculations were repeated after developing &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;idealized&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; models of both the bifurcated and crossed-limbs endografts with straight main bodies and no neck angulation or curved iliac segments. The vector of the total force was directed anterocaudal for both the typical bifurcated and the crossed-limbs configurations, with the forces in the latter slightly reduced and the vertical component accounting for most of the force in both configurations. Idealized crossed-limbs and bifurcated configurations differed only in the force on the iliac limbs, but this difference disappeared in the realistic models. Crossing of the iliac limbs can slightly affect the direction of the displacement forces. Although this configuration can exert larger forces on the limbs than in the bifurcated mode, this effect can be blunted by concomitant modifications in the geometry of the main body and other parts of the endograft, making its hemodynamic behavior resemble that of a typically positioned endograft.