Association Between Aneurysm Shoulder Stress and Abdominal Aortic Aneurysm Expansion A Longitudinal Follow-Up Study

School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China.
Circulation (Impact Factor: 14.43). 10/2010; 122(18):1815-22. DOI: 10.1161/CIRCULATIONAHA.110.939819
Source: PubMed


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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    • "More interestingly, the authors demonstrated that PWS (hazard ratio:25), outweighed gender (hazard ratio:3) as a rupture predictive tool and that after accounting for wall stress and gender, diameter would not predict rupture [18]. Furthermore, low stress values have been associated with slow growth rate in small AAAs [19], whereas rapid growth rate of small AAAs can be strongly related with high values of wall stress at the inflection site between the neck and the sac [20]. "
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    ABSTRACT: Inflammation and the associated recruitment of monocytes/macrophages into the aortic wall is critical in the pathology of abdominal aortic aneurysm (AAA) disease. The mechanisms behind this process are ill defined though wall shear stress (WSS) is known to play a role in leukocyte recruitment. In this study patterns of monocyte deposition and the probability of recruitment in AAA are determined numerically and compared with distributions of WSS. Finite element computational fluid dynamic (CFD) modelling was used to model blood hemodynamics, track monocyte behaviour and determine the magnitude of wall shear stress in rigid walled geometries of generalised AAA dimensions. Pulsatile flow was simulated using a one-way coupled Eulerian-Lagrangian simulation with near-wall particle lift and drag modification. Particle tracking was combined with a non-dimensional distance-to-wall dependent residence time model to observe the probability of cell adhesion.Patterns of WSS were closely related to vortex formation and dissipation in the AAA and monocyte NWPRT was highest in areas of vortex dissipation. Since areas of high deposition overlap with sites of high WSS and WSS is a limiting factor in monocyte recruitment, a WSS-limiter was applied to the NWPRT model.
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