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Increased Peak Wall Stress in Women with Abdominal Aortic Aneurysms
Eric K. Shang, M.D., Derek P. Nathan, MD, Robert C. Gorman, MD, Joseph H. Gorman, III, MD, Grace J. Wang, MD, Edward Y. Woo, MD, Ronald M. Fairman, MD, Benjamin M. Jackson, MD. University of Pennsylvania, Philadelphia, PA, USA.
OBJECTIVE: Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) is a superior predictor of clinical outcomes compared to maximum transverse diameter. Women with AAAs have higher rupture risks at equivalent diameters, with material properties and geometric differences implicated as possible etiologies. The purpose of this study was to investigate possible differences in the PWS of AAAs, which reflects individual aneurysm geometry, between the two genders. METHOD: A total of 20 consecutive men and 20 consecutive women with infrarenal AAAs undergoing CTA were identified. Custom MATLAB image processing algorithms extracted variable wall thickness patient-specific AAA geometries from raw DICOM images. Peak wall stress was calculated by loading the resulting aortic reconstructions with a constant 120 mmHg blood pressure using commercially available FEA solvers in an effort to isolate the role of aneurysm geometry. RESULTS: No significant differences were found between men and women's mean ages (74.5±9.2 vs 75.4±8.2, P=0.75), and maximum transaortic diameters (47.0±7.7 vs 48.5±9.0, P=0.56). PWS was found to be significantly higher in women (277±51 vs 214±62 kPA, P=0.001, see Figure). While mean aortic wall thickness was not significantly different (2.17±0.22 vs 2.26±0.35 mm, P=0.33), women had significantly increased maximum Gaussian curvature (0.031±0.013 vs 0.024±0.010 mm-2, P=0.03). CONCLUSION: PWS calculated using FEA was significantly higher in women with comparably sized aortic aneurysms. Maximum gaussian curvature, a measure of aneurysm morphology, was significantly different between the two groups. These results suggest aneurysm geometry contributes to gender differences in AAA prognosis, and that PWS-derived risk stratification may be gender independent.
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