Age Is Superior to Aortopathy Phenotype as a Predictor of Aortic Mechanics in Patients with Bicuspid Valve

Objectives

Bicuspid aortic valve (BAV) aortopathy is defined by three phenotypes—root, ascending, and diffuse—based on region of maximal aortic dilation. We sought to determine the association between aortic mechanical behavior and aortopathy phenotype versus other clinical variables.

Methods

From 08/01/2016 to 03/01/2022, 375 aortic specimens were collected from 105 patients undergoing elective ascending aortic aneurysm repair for BAV aortopathy. Planar biaxial data (191 specimens) informed constitutive descriptors of the arterial wall that were combined with in vivo geometry and hemodynamics to predict stiffness, stress, and energy density under physiologic loads. Uniaxial testing (184 specimens) evaluated failure stretch and failure Cauchy stress. Boosting regression was implemented to model the association between clinical variables and mechanical metrics.

Results

There were no significant differences in mechanical metrics between the root phenotype (N=33, 31%) and ascending/diffuse phenotypes (N=72, 69%). Biaxial testing demonstrated older age was associated with increased circumferential stiffness, decreased stress, and decreased energy density. On uniaxial testing, longitudinally versus circumferentially oriented specimens failed at significantly lower Cauchy stress (50th [15th, 85th percentiles]: 1.0 [0.7, 1.6] MPa vs. 1.9 [1.3, 3.1] MPa; P<0.001). Age was associated with decreased failure stretch and stress. Elongated ascending aortas were also associated with decreased failure stress.

Conclusions

Aortic mechanical function under physiologic and failure conditions in BAV aortopathy is robustly associated with age and poorly associated with aortopathy phenotype. Data suggesting that the root phenotype of BAV aortopathy portends worse outcomes are unlikely to be related to aberrant, phenotype-specific tissue mechanics.