Biomechanical Properties of the Thoracic Aneurysmal Wall: Differences Between Bicuspid Aortic Valve and Tricuspid Aortic Valve Patients

摘要

Cohort and Tissue HarvestingMechanical TestingHistologyResultsCharacteristics of the Study PopulationCollagen OrganizationFE Model SimulationsIncreased Strength and Collagen-Related Stiffness in the BAV Aneurysmal AortaCommentSupplementary DataReferencesThe prevalence for thoracic aortic aneurysms (TAAs) is significantly increased in patients with a bicuspid aortic valve (BAV) compared with patients who have a normal tricuspid aortic valve (TAV). TAA rupture is a life-threatening event, and biomechanics-based simulations of the aorta may help to disentangle the molecular mechanism behind its development and progression. The present study used polarized microscopy and macroscopic in?vitro tensile testing to explore collagen organization and mechanical properties of TAA wall specimens from BAV and TAV patients.MethodsCircumferential sections of aneurysmal aortic tissue from BAV and TAV patients were obtained during elective operations. The distribution of collagen orientation was captured by a Bingham distribution, and finite element models were used to estimate constitutive model parameters from experimental load-displacement curves.ResultsCollagen orientation was almost identical in BAV and TAV patients, with a highest probability of alignment along the circumferential direction. The strength was almost two times higher in BAV samples (0.834 MPa) than in TAV samples (0.443 MPa; p < 0.001). The collagen-related stiffness (Cf) was significantly increased in BAV compared with TAV patients (Cf?= 7.45 MPa vs 3.40 MPa; p?= 0.003), whereas the elastin-related stiffness was similar?in both groups. A trend toward a?decreased wall thickness was seen in BAV patients (p?= 0.058).ConclusionsThe aneurysmal aortas of BAV patients show a higher macroscopic strength, mainly due to an increased collagen-related stiffness, compared with TAV patients. The increased wall stiffness in BAV patients may contribute to the higher prevalence for TAAs in this group.CTSNet classification:26The Appendix can be viewed in the online version of this article [http://dx.doi.org/10.1016/j.athoracsur.2014.04.042] on http://www.annalsthoracicsurgery.org.The ascending aorta is uniquely designed to cope with the large hemodynamic forces and tissue stresses that are created in the left ventricular outflow tract as the heart contracts, and a proper function of its biomechanical properties is of great importance not only for its own structural and functional integrity but also for the entire vascular system. Biomechanical properties of the aortic wall are mainly determined by the ratio between elastin and collagen, the two major structural proteins of the extracellular matrix [