Biomechanics of Aortic Dissection: A Comparison of Aortas Associated With Bicuspid and Tricuspid Aortic Valves

Figures

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  Figure 1. Aortic specimens excised at the time of surgery are taken for ex vivo biomechanical testing. A, Specimen sampled at both inner and outer curvatures. B, Squares are sampled for (C) biaxial tensile testing and rectangular strips are sampled for (D) delamination testing.

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  Figure 2. Definitions of biomechanical parameters. A, Tangent modulus of elasticity and energy loss is derived from the stress‐strain curve. B, Anisotropy index quantifies the relationship between parameters measured in the longitudinal vs circumferential directions. C, Delamination strength is derived from the average force after the first peak during delamination testing.

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  Figure 3. Biomechanical properties across patient groups. A, Delamination strength (S d) of aneurysms is significantly lower than normal aortas and higher than dissected aortas. Inner curvature (IC; blue solid circles) samples were used for this analysis as it was only the inner curve of the aorta that was available for delamination testing in dissected aortas. B, S d is the same on the IC vs the outer curvature across patient groups. C and D, Aneurysms with bicuspid aortic valves have higher modulus of elasticity (E) than normal aortas and aneurysms with tricuspid aortic valves, especially when measured in the longitudinal direction. E and F, Aneurysms with tricuspid aortic valves have higher energy loss (ΔUL) than either normal aortas or aneurysms with bicuspid aortic valves as measured in both the circumferential and longitudinal directions. G, The anisotropy index (AI) of the modulus of elasticity (E), was the same across groups. H, The AI of ΔUL was more negative for normal aortas than aneurysmal aortas. BAV indicates bicuspid aortic valve; circ, circumferential; long, longitudinal; OC, outer curvature (grey open circles); and TAV, tricuspid aortic valve. Statistics shown are 1‐way…

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  Figure 4. The relationship between delamination strength (S d) of the ascending aorta and clinical parameters. A, S d decreases with age. B, S d is the same between sexes and whether there is a positive smoking history. S d is lower in patients with hypertension. C, S d decreases as aortic diameter increases, D, and this relationship is similar when indexing aortic size to body surface area (BSA). E, Neither aortic stenosis (AS) or aortic regurgitation (AR) had a relationship with S d. F, No relationship was seen with either β‐blockers (BB) or angiotensin‐converting enzyme (ACE) inhibitors/angiotensin receptor blockers (ARBs) and S d. B through F, outer curvature (OC; grey open circles) data shown as inner curvature (IC; blue solid circles) data similar. Statistics shown are linear regression and 2‐way ANOVA post‐test results (Bonferroni): *P<0.05, **P<0.01, ***P<0.001.

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  Figure 5. Biomechanical parameters were evaluated for their associations with delamination strength (S d) of the ascending aortic tissue. The inner curvature (IC) panel includes the relationships between S d and (A) energy loss (ΔUL), (B) aortic stiffness (modulus of elasticity, (E) and (C) anisotropy index (AI) on the inner curve of the aorta. The outer curvature (OC) panel includes the relationships between S d and (D) ΔUL, (E) aortic stiffness, and (F) AI on the outer curve of the aorta. S d decreased as ΔUL of the tissue increased. No relationship was seen between aortic stiffness and S d. There was a significant relationship between AI of ΔUL measured on the OC of the ascending aorta and S d. Statistics shown are 1‐phase decay for (A and D), and linear regression for the rest: ***P<0.001. circ indicates circumferential; and long, longitudinal.

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  Figure 6. Aortic biomechanics is related to underlying aortic wall microstructure. A, Relationship between delamination strength (S d) of ascending aortic tissue during ex vivo biomechanical testing and content of elastin evaluated from colorimetric analysis of Movat pentachrome staining of histological sections of the same aortic specimens. Statistics shown are linear regression: ***P<0.001. B, An example of a histological section from an aortic specimen with higher S d and higher elastin content. There were intact elastin (black) lamellae with preserved vascular smooth muscle cells (purple/pink) and relatively low contents of collagen (yellow). C, An example of a histological section from an aortic specimen with lower S d and lower elastin content. There was profound medial degeneration with extensive elastin (black) fragmentation, loss of smooth muscle cells (purple/pink), and elevated content of collagen (yellow).