Biomechanical characterization of ascending aortic aneurysm with concomitant bicuspid aortic valve and bovine aortic arch.

Studies have shown that patients harboring bicuspid aortic valve (BAV) or bovine aortic arch (BAA) are more likely than the general population to develop ascending aortic aneurysm (AsAA). A thorough quantification of the AsAA tissue properties for these patient groups may offer insights into the underlying mechanisms of AsAA development. Thus, the objective of this study was to investigate and compare the mechanical and microstructural properties of aortic tissues from AsAA patients with and without concomitant BAV or BAA. AsAA (n=20), BAV (n=20) and BAA (n=15) human tissues were obtained from patients who underwent elective AsAA surgery. Planar biaxial and uniaxial failure tests were used to characterize the mechanical and failure properties of the tissues, respectively. Histological analysis was performed to detect medial degenerative characteristics of aortic aneurysm. Individual layer thickness and composition were quantified for each patient group. The circumferential stress-strain response of the BAV samples was stiffer than both AsAA (p=0.473) and BAA (p=0.152) tissues at a low load. The BAV samples were nearly isotropic, while AsAA and BAA samples were anisotropic. The areal strain of BAV samples was significantly less than that of AsAA (p=0.041) and BAA (p=0.004) samples at a low load. The BAA samples were similar to the AsAA samples in both mechanical and failure properties. On the microstructural level, all samples displayed moderate medial degeneration, characterized by elastin fragmentation, cell loss, mucoid accumulation and fibrosis. The ultimate tensile strength of BAV and BAA sampleswere also found to decrease with age. Overall, the BAV samples were stiffer than both AsAA and BAA samples, and the BAA samples were similar to the AsAA samples. The BAV samples were thinnest, with less elastin than AsAA and BAA samples, which may be attributed to the loss of extensibility of these tissues at a low load. No apparent difference in failure mechanics among the tissue groups suggests that each of the patient groups may have a similar risk of rupture.