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Ascending Thoracic Aortic Aneurysm Wall Stresses in Bicuspid vs Tricuspid Aortic Valves
Yue Xuan, Raymond Liu, Henrik Haraldsson, Michael D Hope, David A Saloner, Julius M Guccione, Liang Ge, *Elaine Tseng
UCSF Medical Center and SFVAMC, San Francisco, CA

OBJECTIVES:
Guidelines for repair of bicuspid aortic valve (BAV) associated ascending thoracic aortic aneurysms (aTAA) have been changing, most recently to the same criteria as tricuspid aortic valve (TAV)- associated aTAA unless family history of dissection or sudden death exists. However, rupture or dissection occurs when wall stress exceeds wall strength. Recent studies suggest similar strength of BAV vs TAV aortic aneurysms; however comparative wall stresses between BAV and TAV are unknown. Our hypothesis was that BAV and TAV aTAA had similar wall stresses and our objective was to compare based upon patient-specific aTAA geometries, the wall stresses of BAV vs TAV-aTAA.
METHODS:
Patients with >4.5cm diameter aTAAs were recruited for the study and underwent ECG-gated computed tomography angiography. 3D geometry was reconstructed for each patient to determine patient-specific geometry, which was loaded to systemic pressure after determining pre-stress 0mmHg geometry. Finite element analyses were performed using LS-DYNA solver with user-defined fiber-embedded material model to determine aTAA wall stresses.
RESULTS:
BAV and TAV aTAA patients (BAV=16, TAV=20) were included in the study. Peak first principal wall stress on BAV-aTAA patients was 808269 vs 865328 kPa (p=0.34) for TAV-aTAA patients at systolic pressure, while at diastolic pressure, peak first principal wall stress for BAV-aTAA was 502155 vs 555199 kPa (p=0.27) for TAV-aTAA patients. The peak 1st principal stress was not significantly correlated to the aneurysm diameter (fig 1, R2=0.034 for BAV aneurysms and 0.244 for TAV aneurysms). Peak second principal wall stress on BAV-aTAA patients was 37072 vs 412140 kPa (p=0.21) for TAV-aTAA patients at systolic pressure, while at diastolic pressure, peak second principal wall stress for BAV-aTAA was 25658 vs 275100 kPa (p=0.31) for TAV-aTAA patients at diastolic pressure.
CONCLUSIONS:
For this population of >4.5cm thoracic aortic aneurysms, the 1st and 2nd principal wall stresses was comparable between BAV and TAV-associated aTAA. Given the lack of correlation between peak wall stress and aneurysm diameter, this study highlights the need for patient-specific aneurysm wall stress analysis to determine clinical risk of aortic dissectionn.


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