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

Abstract

Background Current methods for aortic dissection risk assessment are inadequate for patients with ascending aortic aneurysms associated with either bicuspid aortic valves (BAVs) or tricuspid aortic valves (TAVs). Biomechanical testing of aortic tissue may provide novel insights and biomarkers. Methods and Results From March 2017 to August 2019, aneurysmal ascending aortas (BAV=23, TAV=23) were collected from elective aortic surgery, normal aortas from transplant donors (n=9), and dissected aortas from surgery for aortic dissection (n=7). These aortas underwent delamination testing in simulation of aortic dissection. Biaxial tensile testing was performed to determine modulus of elasticity (aortic stiffness), and energy loss (a measure of efficiency in performing the Windkessel function). Delamination strength ( S d ) was lowest in dissected aortas (18±6 mN/mm) and highest in normal aortas (58±16 mN/mm), and aneurysms fell in between, with greater S d in the BAV group (37±10 mN/mm) than the TAV group (27±10 mN/mm) ( P <0.001). Bicuspid aortopathy was associated with greater stiffness ( P <0.001), while aneurysms with TAV demonstrated greater energy loss ( P <0.001). S d decreased by 7.8±1.2 mmol/L per mm per decade of life ( r 2 =0.45, P <0.001), and it was significantly lower for patients with hypertension ( P =0.001). S d decreased by 6.1±2.1 mmol/L per mm with each centimeter increase in aortic diameter ( r 2 =0.15, P =0.007). Increased energy loss was associated with decreased S d ( r 2 =0.41), whereas there was no relationship between S d and aortic stiffness. Conclusions Aneurysms with BAV had higher S d than those with TAV, suggesting that BAV was protective. Energy loss was lower in aneurysms with BAV, and inversely associated with S d , representing a potential novel biomarker.

Gender differences in the dissection properties of ascending thoracic aortic aneurysms

“…The delamination strength values in the present study are much lower than a previous study, which investigated the effect of valve morphology on the dissection properties of ATAAs [ 9 ]. Our delamination strength values of the elderly female patients are similar to the dissection data of ATAAs measured by Chung et al [ 10 ]. and Angouras et al [ 22 ].…”

“…It has been suggested that delamination strength is an important biomechanical indicator, which is helpful to assess the initiation and propagation of AD [ 6 , 9 , 10 ]. Thus, aortas that require lower forces to dissect may have a higher propensity of dissection.…”

“…Hence, particular attention needs to be paid to elderly female patients in the clinical treatment of ATAAs as they may have a higher risk of AD initiation. Although a previous study indicated that delamination strength of the ATAAs was decreased as patient age increased [ 10 ], their dissection data were primarily derived from peeling through the longitudinal strips of aortic tissue. Note that some male patients with ages between 55 and 60 years have remarkably lower delamination strength for their ATAAs ( Fig.…”

Should We Operate on Thoracic Aortic Aneurysm of 5-5.5cm in Bicuspid Aortic Valve Disease Patients?

“…Also, though thoracic aortic aneurysms are more common in BAV patients compared to TAV patients, recent benchtop biomechanical data shows higher longitudinal and circumferential tensile strength and collagen stiffness in resected proximal thoracic aortas of BAV patients compared to TAV patients [ 9 , 10 ]. In addition, a recent study show that in an ex vivo setup, BAV proximal aortic aneurysms have greater resistance to aortic dissection compared to TAV aortic aneuryms [ 11 ].…”

Is this the final answer for the aortopathy with bicuspid aortic valve

“…15 The study of this bicuspid valve and aortopathy continues to attract attention and new findings are being reported. Recently, it has been experimentally demonstrated that bicuspid valves are more dissectionresistant, 16 and the relationship between shear stress and aortic enlargement have been reported using more accurate imaging. 17 Depending on further research, the guidelines for the bicuspid valve may well change in the future, and we hope that more studies using a common definition 18 among researchers will accumulate.…”