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

Abstract

Objectives Studies have shown that patients harboring bicuspid aortic valve (BAV) or bovine aortic arch (BAA) are more likely to develop ascending aortic aneurysm (AsAA) than the general population. A thorough quantification of the AsAA tissue properties for these patient groups may offer insight into the underlying mechanisms of AsAA development in these patients. 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. Materials and methods 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 the medial degenerative characteristics of aortic aneurysm. Individual layer thickness and composition were quantified for each patient group. Results The circumferential (CIRC) response of the BAV samples was stiffer than both AsAA (p = 0.473) and BAA (p = 0.152) tissues at low load. The BAV tissues were nearly isotropic while AsAA and BAA tissues were anisotropic. The areal strain of BAV samples were significantly less than AsAA (p = 0.041) and BAA (p = 0.004) tissues 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 tissues were also found to decrease with age. Conclusions The BAV tissues were stiffer than both AsAA and BAA tissues, and the BAA tissues were similar to the AsAA tissues. The BAV samples were thinnest with less elastin than AsAA and BAA samples, which may attribute to the loss of extensibility at low load of these tissues. No apparent difference in failure mechanics among the tissue groups suggests that each of the patient groups may have a similar risk of rupture.

Biomechanical properties of the thoracic aorta in Marfan patients

“…Additionally, the circumferential and longitudinal directions of the MFS samples were determined by visual inspection, possibly affecting results. However, the MFS results obtained in this study are consistent with other ex vivo studies (14,15,24) and thus the visual judgment of axial and circumferential directions is not believed to have significantly affected the results presented herein. Lastly, quantitative microstructural analysis may provide additional support for the presented histological findings.…”

“…Additionally, Pham et al found BAV patients, which have been structurally and mechanically linked to MFS patients (13,14,23), to have significantly more isotropic aortic tissue than other AsAA patients, as also found in MFS patients in the current study (24). Pham also found a trend of age-related thickening in BAV tissue, agreeing with our MFS findings.…”

Stent and leaflet stresses in 26-mm, third-generation, balloon-expandable transcatheter aortic valve

“…BAV had greater collagen 291 stiffness but equivalent elastin stiffness as TAV-aTAA to account for the overall greater wall strength. In 292 contrast, Sun et al 27 demonstrated that failure mechanics between BAV and TAV-aTAA were equivalent, 293 BAV was stiffer than TAV-aTAA, had less elastin, and was thinner. Histologically, studies 28 have 294 demonstrated accumulation of mucoid material, elastin fragmentation, and change of smooth muscle cell 295 orientation in BAV-aTAA compared with TAV-aTAA.…”

Patient-specific finite element analysis of ascending aorta aneurysms

“…In a previous study from our group (30), the tissue elastic and failure strength properties were characterized for AsAA tissues resected from patients undergoing elective AsAA repair. Patients with concomitant bicuspid aortic valve (BAV) and bovine aortic arch (BAA) were studied specifically to gain a better understanding of why these patients may be more susceptible to AsAA and dissection (10,14,42).…”

“…The main limitation of the analytical method (23) was that an idealized cylindrical AsAA geometry was assumed and thus the effect of the patient's specific AsAA geometry on the vessel wall stress was not taken into account. To address this limitation, in the present study, patient-specific AsAA FE models were constructed for a total of 27 patients studied previously (23,30), for whom cardiac computed tomography (CT) scans were obtained. Utilizing this unique matching dataset of individual patient imaging data, and AsAA tissue elastic and failure properties (30), AsAA rupture risk was assessed on a truly patient-specific level using FE.…”