Eric K. Shang, Derek P. Nathan, Ronald M. Fairman, Edward Y. Woo, Grace J. Wang, Robert C. Gorman, Joseph H. Gorman III, Benjamin M. Jackson
Hospital of the University of Pennsylvania, Philadelphia, PA.
OBJECTIVES: Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) predicts clinical outcomes better than diameter alone. Prior models assume uniform wall thickness (UWT). We hypothesize that the inclusion of locally variable wall thickness (VWT) into FEA of AAAs will improve its ability to predict clinical outcomes.
METHODS: Patients with AAAs (n=26) undergoing radiologic surveillance were identified. Custom MATLAB algorithms generated UWT and VWT aortic geometries from CTA images, which were subsequently loaded with systolic blood pressure using FEA. PWS and aneurysm growth (as a proxy for rupture risk and the need for repair) were examined.
RESULTS: The average radiologic follow-up time was 22.0±13.6 months and the average aneurysm growth rate was 2.8±1.7 mm/year. PWS in VWT models significantly differed from PWS in UWT models (238±68 vs. 212±73 kPa, p=0.025). In our sample, initial aortic diameter was not found to be correlated with aneurysm growth (r=0.26, p=0.19). A stronger correlation was found between aneurysm growth and PWS derived from VWT models as compared to PWS from UWT models (r=0.86 vs r=0.58, p=0.032 by Fisher's r to Z transformation (see Figure 1)).
CONCLUSIONS: The inclusion of locally variable wall thickness significantly improved the correlation between PWS and aneurysm growth. Aortic wall thickness should be incorporated into future FEA models to accurately predict clinical outcomes.
AUTHOR DISCLOSURES: R. M. Fairman: Nothing to disclose; R. C. Gorman: Nothing to disclose; J. H. Gorman III: Nothing to disclose; B. M. Jackson: Nothing to disclose; D. P. Nathan: Nothing to disclose; E. K. Shang: Nothing to disclose; G. J. Wang: Nothing to disclose; E. Y. Woo: Nothing to disclose.
Plots showing the relationships between aneurysm expansion and initial aortic diameter, peak wall stress from uniform wall thickness models and peak wall stress from variable wall thickness models.
Posted April 2013