Regional and directional variations in the mechanical properties of ascending thoracic aortic aneurysms

This study aimed to assess regional and directional differences in the mechanical properties of ascending thoracic aortic aneurysms (ATAA). Whole fresh ATAA were taken from twelve patients, undergoing elective surgical repair, and cut into tissue specimens. These were divided into groups according to direction and region, and subjected to uniaxial testing beyond rupture. In the majority of tests, the inner layers of the aortic wall ruptured first; failure stress (measure of tissue strength) and peak elastic modulus (measure of tissue stiffness) were significantly higher circumferentially in all regions. Marked heterogeneity was evident in the mechanical properties of ATAA, with the anterior region longitudinally being the weakest and least stiff of all regions. No correlation was found between failure stress and ATAA diameter or patient age. Failure stress showed inverse correlations with wall thickness and direct correlations with peak elastic modulus. The current information, relating to regional and directional differences, may provide a better understanding of the mechanism responsible for the development of circumferential tears of the inner aortic wall layers in ATAA dissections.