Biomechanical changes in abdominal aortic aneurysms involve a prolonged post-failure phase

BackgroundPrevious studies characterizing the tensile strength of abdominal aortic aneurysms (AAAs) have disregarded the post-failure phase during which rupture propagates.ObjectiveTo identify aneurysm-induced changes in the post-failure phase of the intact infra-renal aortic wall, examining its three layers.MethodsWe analyzed ex vivo tensile tests on tissues from 27 AAA patients and 27 age-matched autopsy subjects.ResultsThe failure stress of the intact wall circumferentially and the intimal failure stress in both circumferential and longitudinal directions were significantly lower (p < 0.05) in AAAs than in non-aneurysmal aortas (NAAs). Failure stretch showed no significant changes. However, the pre-failure stretches of the intact wall and media circumferentially were higher (p < 0.05) in AAAs, as were the post-failure stretches of the intact wall and media in both directions and the adventitia circumferentially. The pre-extensions of the media and adventitia were also higher (p < 0.05) when coupled to the intact wall.ConclusionsThe study demonstrates an earlier onset of damage in AAAs and a strength decrease, indicating weakening. The medial and adventitial layers contribute more in determining AAA intact-wall properties. Their greater capacity for post-failure stretch may delay rupture progression outward, preserving the integrity of the entire aortic thickness despite initiation in the weakened intima.