Regional distribution of delamination strength in ascending thoracic aortic aneurysms

Considering that the biomechanical factors underlying aortic dissection remain poorly understood as does the rationale for the anatomic localization of the dissection channel, we have attempted to determine the regional distribution of delamination/tensile strengths of ascending thoracic aortic aneurysm wall tissue. Whole aneurysms were taken from seventeen patients undergoing elective surgery and cut into a couple of specimens per quadrant and direction. The specimens were subjected to delamination- and tensile-testing, from which average peel tension (=delamination strength) and failure stress (=tensile strength) were assessed. Histology revealed no differences with region and direction in the roughness of the delaminated surfaces of the inner (intima with most of media) and outer layers (leftover media with adventitia). Compared to the right, the left lateral region exhibited significantly higher thickness and peel tension in both directions, but lower failure stress of the inner and outer layers longitudinally. Failure stress of the inner layers mostly but also of the outer layers was significantly higher circumferentially than longitudinally, with significantly higher values for the outer compared to the inner layers. Differing heterogeneity was evidenced in the delamination and tensile strength of aneurysmal tissue, with important implications for dissection propagation. Particularly, the increased resistance to propagation in the left lateral region helps address the question why part of the circumference, characteristically the right lateral wall, is involved by the dissection and the other part of the aortic wall remains intact. The deterioration of delamination strength with aging suggests the greater potential of aged individuals for dissection propagation.