Intra-Patient Heterogeneity of Mechanical and Anatomical Properties in Thoracic Aortic Wall: An Ex Vivo Study Comparing Patients with Bicuspid and Tricuspid Aortic Valve Aortopathy

TL;DR

This study compares the variation in aortic wall thickness and mechanical properties in patients with bicuspid and tricuspid aortic valve disease, finding greater mechanical than anatomical heterogeneity.

Contribution

The study is the first to thoroughly investigate intra-patient heterogeneity of aortic wall characteristics in bicuspid and tricuspid aortic valve disease.

Findings

Aortic wall thickness heterogeneity is less significant than mechanical properties heterogeneity.

Maximum elastic modulus heterogeneity is reverse-correlated with patient age in bicuspid aortic valve patients.

No significant differences in intra-patient variability were found between bicuspid and tricuspid aortic valve groups.

Abstract

Background: The ex vivo evaluation of the aortic wall aims to identify potential risk factors predictive of acute aortic syndrome. The comparison of aortic wall properties in patients with bicuspid aortic disease versus those with tricuspid aortic disease has been the subject of many studies. However, the heterogeneity of aortic wall characteristics in individual patients has never been thoroughly investigated. In this study, we focused on comparing the heterogeneity of aortic wall characteristics in patients with bicuspid (BAV) and tricuspid (TAV) aortic valve disease. Materials and Methods: Out of 113 patients enrolled in our cumulative study on the ex-vivo evaluation of the aortic wall, in patients with dilated ascending aorta, 56 patients with >3 specimens taken from the anterior wall were selected for the present study. The heterogeneity of anatomical characteristics (aortic wall thickness) was assessed by measuring the coefficient of variability (cV). In 35 patients, furthermore, mechanical (uniaxial ultimate stress–strain test) characteristics heterogeneity was also evaluated. Intra-patient mechanical and anatomical variability was then compared between the BAV and TAV groups. Results: Heterogeneity of aortic wall thickness was significantly less important compared to heterogeneity of mechanical properties: peak strain (Pstr p = 0.0042), peak stress (PS p = 0.001) and maximum elastic modulus (EM p = 0.001). Only EM heterogeneity was significantly reverse-correlated to patient’s age (p = 0.0005), and this correlation was peculiar for patients with BAV. In BAV patients, furthermore, age > 66 was associated with a significantly superior EM heterogeneity (p = 0.008). A direct comparison of anatomical and mechanical intra-patient variability between BAV and TAV groups, however, did not show significant differences. Discussion: Our study clearly demonstrates that the anatomical and mechanical characteristics of the aortic wall in patients with aortic dilation are not homogeneous. The heterogeneity of aortic wall thickness appears to be less significant than that of mechanical properties, thus confirming a limited correlation between anatomical and mechanical characteristics. The comparison between the BAV and TAV groups revealed limited peculiarities, further suggesting a preservation of the mechanical properties of the aortic wall in patients with bicuspid aortic disease and, therefore, without a peculiar mechanical properties-related increased risk of acute aortic syndrome.

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