Effects of aneurysm on the mechanical properties and histologic structure of aortic sinuses.

Background: Aortic root aneurysms are relatively uncommon but their rupture is a detrimental event with acute hemodynamic compromise and high mortality, and there are few available data on their mechanical properties, although aneurysm rupture occurs when hemodynamic stresses exceed wall strength. This study aimed to fill this gap by examining the effect of aneurysm on the mechanical and structural properties of aortic sinuses.

Methods: Sinus tissue was procured from 16 aneurysmal patients during surgical repair and from 18 age-matched nonaneurysmal autopsy subjects, and grouped by age (young versus old), region (left versus right versus noncoronary), and direction (circumferential versus longitudinal). The tissue was submitted to histologic evaluation of elastin/collagen contents and to mechanical testing beyond rupture for the determination of failure properties and material characterization by the Fung-type model.

Results: Contrasting the direction-dependent (anisotropic) material constants and failure properties, and the primarily circumferential reinforcement of elastin/collagen fibers in healthy sinuses, near-similar (isotropic) properties and arbitrarily aligned fibers were found in the aneurysmal right and left coronary sinuses, together with less anisotropic properties in the aneurysmal noncoronary sinus. Variations between aneurysmal and healthy sinuses were comparable in young and old subjects. The former displayed significantly higher failure stress, failure stretch, and peak elastic modulus, justified by their increased elastin/collagen contents.

Conclusions: We submit evidence of more isotropic histomechanical properties in the aneurysmal sinuses that seem consistent with the more axisymmetric stresses exerted on them owing to their more spherical shape, compared with the nondilated healthy sinuses that presented marked anisotropic properties.