Wall Tensile Stress Maps of Human Aneurysmal Aorta Demonstrate a High Biaxiality Ratio Corresponds with Wall Tissue Microstructure and Local Oxidative Stress Response Distinctly for Bicuspid and Tricuspid Aortic Valve Patients.

PURPOSE

We sought to estimate imaging-derived aortic biomechanical properties and correlate regional tensile stress, extracellular matrix (ECM) architecture, and cellular biology to improve upon diameter-based aortic surgery guidelines.

METHODS

Electrocardiogram (ECG)-gated computed tomographic angiography (CTA) was utilized to model regional aortic wall biomechanical properties. Using an established constitutive model, we derived wall tensile stress and strain maps from CTAs of patients who underwent ascending aortic replacement for aneurysmal disease. We quantitatively and qualitatively assessed ECM microarchitecture, matrix metalloproteinase (MMP) activity, and aortic smooth muscle cell (SMC) behavior in regions of low and high biaxiality ratio (B), defined as the ratio of longitudinal to circumferential tensile stress. Patients with a tricuspid aortic valve (TAV) and bicuspid aortic valve (BAV) were considered separately.

RESULTS

Gated CTAs demonstrated heterogeneous aortic wall strain. Regions of high B qualitatively exhibited disarrayed elastin fibers and localized ECM degeneration. MMP activity was significantly increased in regions of high vs low B in TAV patients only. SMCs isolated from regions of high B exhibited significantly decreased viability in response to oxidative stress in BAV but not TAV patients. There were no differences in SMC contractility or expression of SMC phenotypic markers in regions of low and high B.

CONCLUSION

Non-invasive mapping of relative wall tensile stress qualitatively colocalized with ECM microarchitectural disruption and decreased SMC viability distinctly for BAV and TAV patients. This observation contributes to our improved understanding of the relationship between aortic wall structure and biomechanics in ascending aortic disease for patients with different valve types. Biaxial tensile stress mapping, combined with dynamic imaging (i.e., echo, ECG-gated CTA), may contribute to tailored risk stratification for thoracic aortic aneurysm.