Elsevier

The Annals of Thoracic Surgery

Volume 96, Issue 6, December 2013, Pages 2147-2154
The Annals of Thoracic Surgery

Original article
Adult cardiac
Differential Tensile Strength and Collagen Composition in Ascending Aortic Aneurysms by Aortic Valve Phenotype

https://doi.org/10.1016/j.athoracsur.2013.07.001Get rights and content

Background

Ascending thoracic aortic aneurysm (ATAA) predisposes patients to aortic dissection and has been associated with diminished tensile strength and disruption of collagen. Ascending thoracic aortic aneurysms arising in patients with bicuspid aortic valve (BAV) develop earlier than in those with tricuspid aortic valves (TAV) and have a different risk of dissection. The purpose of this study was to compare aortic wall tensile strength between BAV and TAV ATAAs and determine whether the collagen content of the ATAA wall is associated with tensile strength and valve phenotype.

Methods

Longitudinally and circumferentially oriented strips of ATAA tissue obtained during elective surgery were stretched to failure, and collagen content was estimated by hydroxyproline assay. Experimental stress-strain data were analyzed for failure strength and elastic mechanical variables: α, β, and maximal tangential stiffness.

Results

The circumferential and longitudinal tensile strengths were higher for BAV ATAAs when compared with TAV ATAAs. The α and β were lower for BAV ATAAs when compared with TAV ATAAs. The maximal tangential stiffness was higher for circumferential when compared with longitudinal orientation in both BAV and TAV ATAAs. The amount of hydroxyproline was equivalent in BAV and TAV ATAA specimens. Although there was a moderate correlation between the collagen content and tensile strength for TAV, this correlation is not present in BAV.

Conclusions

The increased tensile strength and decreased values of α and β in BAV ATAAs despite uniform collagen content between groups indicate that microstructural changes in collagen contribute to BAV-associated aortopathy.

Section snippets

Tissue Harvest

Whole, fresh, nondissecting ascending aortic specimens were harvested as an intact tubular structure (Fig 1A) from patients with BAV (age, 54 ± 4 years; diameter, 50 ± 5 mm, mean ± standard deviation; n = 23) and TAV (age, 66 ± 11 years; diameter, 57 ± 14 mm; n = 15) undergoing elective surgery. All tissues were excised after obtaining informed patient consent in accordance with a study protocol approved by our institutional review board. The tissue was harvested from above the sinuses of

Results

A total of 23 ATAAs with BAV and 15 ATAAs with TAV were included in this study. The average maximal orthogonal diameter of the aorta was 50 ± 5 mm for BAV versus 57 ± 14 mm for TAV (p = 0.15). The age discrepancy noted is consistent with the clinical observation that BAV ATAAs present 10 to 20 years earlier than patients with TAV and ATAA [17]. From these ATAAs, 178 samples were tensile tested; 15 of those were either slipped or broke at the clamp, and hence were discarded from data analysis.

Comment

Aortic dissection or rupture represents a mechanical failure of the aortic wall, which can occur when aortic wall integrity is altered. Despite a higher percentage of patients with BAV compared with TAV among the aortic dissection population than among the general population [18], no investigation has been done, to our knowledge, on the condition of ATAA wall tensile strength with respect to valve phenotype. This study found differences in the wall strength between ATAAs from BAV and TAV

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These authors contributed equally to this work.

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