Association Between Aneurysm Shoulder Stress and Abdominal Aortic Aneurysm Expansion A Longitudinal Follow-Up Study
ABSTRACT Aneurysm expansion rate is an important indicator of the potential risk of abdominal aortic aneurysm (AAA) rupture. Stress within the AAA wall is also thought to be a trigger for its rupture. However, the association between aneurysm wall stresses and expansion of AAA is unclear.
Forty-four patients with AAAs were included in this longitudinal follow-up study. They were assessed by serial abdominal ultrasonography and computed tomography scans if a critical size was reached or a rapid expansion occurred. Patient-specific 3-dimensional AAA geometries were reconstructed from the follow-up computed tomography images. Structural analysis was performed to calculate the wall stresses of the AAA models at both baseline and final visit. A nonlinear large-strain finite element method was used to compute the wall-stress distribution. The relationship between wall stresses and expansion rate was investigated. Slowly and rapidly expanding aneurysms had comparable baseline maximum diameters (median, 4.35 cm [interquartile range, 4.12 to 5.0 cm] versus 4.6 cm [interquartile range, 4.2 to 5.0 cm]; P=0.32). Rapidly expanding AAAs had significantly higher shoulder stresses than slowly expanding AAAs (median, 300 kPa [interquartile range, 280 to 320 kPa] versus 225 kPa [interquartile range, 211 to 249 kPa]; P=0.0001). A good correlation between shoulder stress at baseline and expansion rate was found (r=0.71; P=0.0001).
A higher shoulder stress was found to have an association with a rapidly expanding AAA. Therefore, it may be useful for estimating the expansion of AAAs and improve risk stratification of patients with AAAs.
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ABSTRACT: The mechanical behavior of aortic stent-grafts plays an important role in the success of endovascular surgery for aneurysms. In this study, finite element analysis was carried out to simulate the expansion of five marketed stent-graft iliac limbs and to evaluate quantitatively their mechanical performances. The deployment was modeled in a simplified manner according to the following steps: stent-graft crimping and insertion in the delivery sheath, removal of the sheath and stent-graft deployment in the aneurysm, application of arterial pressure. In the most curved aneurysm and for some devices, a decrease of stent-graft cross-sectional area up to 57% was found at the location of some kinks. Apposition defects onto the arterial wall were also clearly evidenced and quantified. Aneurysm inner curve presented significantly more apposition defects than outer curve. The feasibility of finite element analysis to simulate deployment of marketed stent-grafts in curved aneurysm models was demonstrated. The influence of aneurysm tortuosity on stent-graft mechanical behavior shows that increasing vessel curvature leads to stent-graft kinks and inadequate apposition against the arterial wall. Such simulation approach opens a very promising way towards surgical planning tools able to predict intra and/or post-operative short-term stent-graft complications.International Journal for Numerical Methods in Biomedical Engineering 01/2015; DOI:10.1002/cnm.2698 · 1.54 Impact Factor
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ABSTRACT: In this exploratory study, we used ultrasound speckle-tracking methods, originally used for analyzing cardiac wall motion, to evaluate aortic wall motion. We compared 19 abdominal aortic aneurysm (AAA) patients with 10 healthy volunteers (diameter, 48 mm vs. 15 mm). Motion pictures of the axial view of the aneurysm using ultrasonography were analyzed. Circumferential strain and strain rate at 6 equally divided segments of the aorta were semiautomatically calculated. We termed 'peak' strain and strain rate as the maximum of strain and strain rate in a cardiac cycle for each segment. We also evaluated the coefficient of variation of peak strain rate for the six segments. In the aneurysm and control groups, the mean values of peak strain along the 6 segments were 1.5% ± 0.6% vs. 4.7% ± 1.6% (p <0.0001), respectively. The coefficient of variation of the peak strain rate was higher in the AAA group (0.74 ± 0.20) than in the control group (0.56 ± 0.12; p <0.05). Aortic wall compliance decreased in the more atherosclerotic AAA group. The higher relative dispersion of strain rates in the AAA group is indicative of the inhomogeneous movement of the aortic wall.Annals of Vascular Diseases 01/2014; 7(4):393-8. DOI:10.3400/avd.oa.14-00067
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ABSTRACT: A mathematical approach of blood flow within an abdominal aortic aneurysm (AAA) with intraluminal thrombus (ILT) is presented. The macroscale formation of ILT is modeled as a growing porous medium with variable porosity and permeability according to values proposed in the literature. The model outlines the effect of a porous ILT on blood flow in AAAs. The numerical solution is obtained by employing a structured computational mesh of an idealized fusiform AAA geometry and applying the Galerkin weighted residual method in generalized curvilinear coordinates. Results on velocity and pressure fields of independent cases with and without ILT are presented and discussed. The vortices that develop within the aneurysmal cavity are studied and visualized as ILT becomes more condensed. From a mechanistic point of view, the reduction of bulge pressure, as ILT is thickening, supports the observation that ILT could protect the AAA from a possible rupture. The model also predicts a relocation of the maximum pressure region toward the zone proximal to the neck of the aneurysm. However, other mechanisms, such as the gradual wall weakening that usually accompany AAA and ILT formation, which are not included in this study, may offset this effect.Computer Methods in Biomechanics and Biomedical Engineering 01/2015; DOI:10.1080/10255842.2014.989389 · 1.79 Impact Factor