The Effects of Anisotropy on the Stress Analyses of Patient-Specific Abdominal Aortic Aneurysms

Abstract

The local dilation of the infrarenal abdominal aorta, termed an abdominal aortic aneurysm (AAA), is often times asymptomatic and may eventually result in rupture-an event associated with a significant mortality rate. The estimation of in-vivo stresses within AAAs has been proposed as a useful tool to predict the likelihood of rupture. For the current work, a previously-derived anisotropic relation for the AAA wall was implemented into patient-specific finite element simulations of AAA. There were 35 AAAs simulated in the current work which were broken up into three groups: elective repairs (n = 21), non-ruptured repairs (n = 5), and ruptured repairs (n = 9). Peak stresses and strains were compared using the anisotropic and isotropic constitutive relations. There were significant increases in peak stress when using the anisotropic relationship (p < 0.001), even in the absence of the ILT (p = 0.014). Ruptured AAAs resulted in elevated peak stresses as compared to non-ruptured AAAs when using both the isotropic and anisotropic simulations, however these comparisons did not reach significance (p(ani) = 0.55, p(iso) = 0.73). While neither the isotropic or anisotropic simulations were able to significantly discriminate ruptured vs. non-ruptured AAAs, the lower p-value when using the anisotropic model suggests including it into patient-specific AAAs may help better identify AAAs at high risk.

Systematic Review of Circulating, Biomechanical, and Genetic Markers for the Prediction of Abdominal Aortic Aneurysm Growth and Rupture

“…Aortic peak wall stress (PWS) was investigated as a marker for AAA rupture in 9 studies 60, 62, 63, 64, 66, 72, 73, 74, 75. In 7 studies, significantly higher PWS (ranging 1.29–1.66‐fold higher) was found in ruptured (and symptomatic) AAA patients than in asymptomatic AAA patients (2 low risk, 4 medium risk, and 1 high risk of bias; total n=536).…”

Patient-Based Abdominal Aortic Aneurysm Rupture Risk Prediction with Fluid Structure Interaction Modeling

“…57,60 This strongly suggests that isotropic wall material models may underestimate the risk of rupture, and that anisotropic material models should be employed for a more accurate prediction of rupture risk. The ILT in all simulations appeared to have provided a cushioning effect.…”

Intracranial Aneurysmal Pulsatility as a New Individual Criterion for Rupture Risk Evaluation: Biomechanical and Numeric Approach (IRRAs Project)

“…5 The problem is the lack of data on mechanical properties of cerebral arteries and aneurysms; most of the studies based on an FSI 6-10 framework do not use experimental mechanical behavior of the aneurysm wall as input. A few exceptions exist for abdominal aorta aneurysms 11,12 but not for intracranial aneurysms until recently when, in a study by Costalat et al, 13 the aneurysm wall properties were characterized and a classification of aneurysm wall behavior was carried out. One of the main conclusions of this work was that the clinical status of the aneurysm (unruptured, preruptured, and ruptured) was strongly correlated with the mechanical behavior of the aneurysm wall and, hence, a classification was proposed (stiff, intermediate, and soft).…”