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Effect of aneurysm on the mechanical dissection properties of the human ascending thoracic aorta - PubMed

Comparative Study

Effect of aneurysm on the mechanical dissection properties of the human ascending thoracic aorta

Salvatore Pasta et al. J Thorac Cardiovasc Surg. 2012 Feb.

Abstract

Objectives: The acute dissection of an ascending thoracic aortic aneurysm (ATAA) represents a devastating separation of elastic layers occurring when the hemodynamic loads on the diseased wall exceed the adhesive strength between layers. At present, the mechanics underlying aortic dissection are largely unclear, and the biomechanical delamination properties of the aneurysmal aorta are not defined. Individuals with bicuspid aortic valve (BAV) are particularly predisposed to ascending aortic aneurysm formation, with a marked risk of aortic dissection. The purpose of this study was to evaluate and compare the dissection properties of nonaneurysmal and aneurysmal human ascending thoracic aorta from patients with BAV morphology or normal tricuspid aortic valve (TAV) morphology using biomechanical delamination testing.

Methods: The influence on the delamination strength (S(d)) of the aorta associated with BAV was compared with that in patients with TAV. After complete delamination of ATAA tissue samples, tensile tests were performed on each delaminated half for comparison of their tensile strengths.

Results: The results showed that the aneurysmal aortas with BAV and TAV have lower S(d) than nonaneurysmal aortas and that ATAA with BAV has a lower S(d) than that with TAV. We have found a significant difference in S(d) between longitudinal and circumferential directions of the nondiseased aorta, suggesting anisotropic dissection properties.

Conclusions: The tensile testing results suggest that the weaker intimal half of the aortic wall might fail before the outer adventitial half. Scanning electron microscope analyses suggest different failure modalities of dissection between the two morphologies, and the lower S(d) in ATAAs appears to be associated with a disorganized microstructure. BAV ATAAs have a lower S(d) than TAV ATAAs, suggesting a greater propensity for aortic dissection.

Published by Mosby, Inc.

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Figures

FIGURE 1.
FIGURE 1.

A, Photograph of representative specimen for delamination test showing through-thickness incision for creating initial dissection plane. B, Schematic experimental setup of delamination testing.

FIGURE 2.
FIGURE 2.

Delamination profiles for A, three longitudinal (LONG) and B, three circumferential (CIRC) strips cut from same bicuspid aortic valve (BAV) aneurysm harvested from 56-year-old male patient with aortic diameter of 46 mm. Dashed lines represent average of mean values of peel tension (Tpeel) for all LONG and CIRC strips and taken as delamination strength (Sd) in LONG and CIRC directions for patient, respectively.

FIGURE 3.
FIGURE 3.

A, Delamination strength in both longitudinal (LONG) (black squares) and circumferential (CIRC) (white squares) orientations. *Significantly different from LONG nonaneurysmal aorta (P<.05). **Significantly different from CIRC nonaneurysmal aorta (P<.05). †Significantly different from CIRC nonaneurysmal aorta (P<.05). B, Delamination strength of aneurysmal aorta with bicuspid aortic valve (BAVext, age) extrapolated (calculated) at age of each of patients with tricuspid aortic valve (TAV) in both LONG (black squares) and CIRC (white squares) directions for n = 8 specimens. *Significantly different from LONG nonaneurysmal aorta (P<.05). **Significantly different from CIRC nonaneurysmal aorta (P<.05). †Significantly different from CIRC nonaneurysmal aorta (P<.05). C, Delamination strength of aneurysmal aorta with BAV (BAVext, dia) extrapolated at aneurysm diameter of each patient with TAV in both LONG (black squares) and CIRC (white squares) directions for n = 8 specimens. *Significantly different from LONG aneurysmal aorta with BAVext (P<.05). **Significantly different from CIRC aneurysmal aorta with BAVext (P<.05). D, Tensile strength in LONG and E, CIRC directions for intimal surface and delaminated plane (INT-DEL) halves (black squares) and adventitial surface and delaminated plane (ADV-DEL) halves (white squares). *Significantly different from INT-DEL LONG BAV ascending thoracic aortic aneurysm (ATAA) (P<.001). **Significantly different from INT-DEL LONG BAV ATAA (P = .016). †Significantly different from INT-DEL CIRC TAV ATAA (P = .024).

FIGURE 4.
FIGURE 4.

A, Representative scanning electron microscope (SEM) images of fracture surfaces of nonaneurysmal and ascending thoracic aortic aneurysm (ATAA) with bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV) in longitudinal (LONG) and circumferential (CIRC) direction. B, High magnification image of CIRC TAV ATAA for intimal surface and delaminated plane (INT-DEL) half showing bundles of broken elastin fibers (F) existing between elastic sheets (E). Fibers act as bridge between halves in fracture modality called “fiber bridging” in delamination testing.

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