Loss of Mechanical Directional Dependency of the Ascending Aorta with Severe Medial Degeneration

Abstract Biomechanical characterization of the aortic wall may help risk stratify patients with aneurysms. We investigated the degree of anisotropy, the directional dependency of mechanical properties, in control and aneurysmal ascending aortic tissue. We hypothesized that medial degeneration and aortic wall remodeling as found in aneurysmal tissue, alters energy loss in both the circumferential and longitudinal directions thereby reducing anisotropy. Aneurysmal and control ascending aortic tissue excised during surgery was subjected to biaxial tensile testing. Stress–strain relationships were collected in the circumferential and longitudinal directions; from this data, the mechanical properties of energy loss and the apparent modulus of elasticity were derived and the associated anisotropy indices were calculated. Movat pentachrome histological staining was performed and aortic wall medial degeneration was quantified. Energy loss was greater in the circumferential than the longitudinal direction demonstrating significant anisotropy in both normal and aneurysmal aortas ( P