Ascending aortic aneurysm haemodynamics are associated with aortic wall biomechanical properties

Abstract

OBJECTIVES The effect of aortic haemodynamics on arterial wall properties in ascending thoracic aortic aneurysms (ATAAs) is not well understood. We aim to delineate the relationship between shear forces along the aortic wall and loco-regional biomechanical properties associated with the risk of aortic dissection. METHODS Five patients with ATAA underwent preoperative magnetic resonance angiogram and four-dimensional magnetic resonance imaging. From these scans, haemodynamic models were constructed to estimate maximum wall shear stress (WSS), maximum time-averaged WSS, average oscillating shear index and average relative residence time. Fourteen resected aortic samples from these patients underwent bi-axial tensile testing to determine energy loss (ΔUL) and elastic modulus (E10) in the longitudinal (ΔULlong, E10long) and circumferential (ΔULcirc, E10circ) directions and the anisotropic index (AI) for each parameter. Nine resected aortic samples underwent peel testing to determine the delamination strength (Sd). Haemodynamic indices were then correlated to the biomechanical properties. RESULTS A positive correlation was found between maximum WSS and ΔULlong rs=0.75, P = 0.002 and AIΔUL (rs=0.68, P=0.01). Increasing maximum time-averaged WSS was found to be associated with increasing ΔULlong (rs=0.73, P = 0.003) and AIΔUL (rs=0.62, P=0.02). Average oscillating shear index positively correlated with Sd (rs=0.73,P=0.04). No significant relationship was found between any haemodynamic index and E10, or between relative residence time and any biomechanical property. CONCLUSIONS Shear forces at the wall of ATAAs are associated with local degradation of arterial wall viscoelastic hysteresis (ΔUL) and delamination strength, a surrogate for aortic dissection. Haemodynamic indices may provide insights into aortic wall integrity, ultimately leading to novel metrics for assessing risks associated with ATAAs.

Elastin integrity in bicuspid valve-associated aortopathy is associated with altered biomechanical properties and influenced by age

“…However, our study suggests that the effect on the resulting biomechanics may be more complex with the interplay between aortic disease and aging. Given that the BAV aortic wall exhibits considerable regional heterogeneity in enzymatic activity and histopathology ( 5 - 10 ), both of which are influenced by valve-mediated hemodynamics that is itself influenced by patient age ( 36 ), our data provides a direct interrogation of the elastin integrity and mechanical properties, and build on previous work by showing that these relationships in the BAV aorta are further influenced by age, and warrant more nuanced stratification of this heterogeneous patient population.…”

“…BAV aortopathy is characterized by elastin fiber degeneration within the aortic wall, as well as aberrant proximal aortic biomechanics (3,22,23). However, the relationship between the two, especially with respect to age Heterogeneous aortic wall remodeling is welldocumented in the BAV aorta (5)(6)(7)(8)(9)(10). Compared to tricuspid aortic valve (TAV), histopathological studies support a unique remodeling process in the BAV aortic wall where heterogeneous expression of disease corresponds with both the cusp fusion pattern as well as valve-mediated hemodynamics (4,(6)(7)(8)(9)11).…”

“…Heterogeneous aortic wall remodeling is well-documented in the BAV aorta ( 5 - 10 ). Compared to tricuspid aortic valve (TAV), histopathological studies support a unique remodeling process in the BAV aortic wall where heterogeneous expression of disease corresponds with both the cusp fusion pattern as well as valve-mediated hemodynamics ( 4 , 6 - 9 , 11 ).…”

“…Abnormal histopathology within the BAV aortic wall is a well-accepted macroscopic manifestation of microscopic extracellular matrix changes mediated by cellular proteins including matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) (1,3). Our group and others previously showed that valve-mediated hemodynamics influence the expression of aortic remodeling in BAVassociated aortopathy (4)(5)(6)(7)(8)(9)(10), and that regional differences in hemodynamics predict both the regional expression of histopathological disease within these aortas as well as degree of elastin fiber derangement-a key mediator of aortic wall mechanical properties (8,9,11).…”

Modelling blood flow in patients with heart valve disease using deep learning: A computationally efficient method to expand diagnostic capabilities in clinical routine

“…These two hemodynamic parameters are chosen based on their clinical relevance. Static pressure derived TPG is the primary parameter for AS diagnostic and treatment (30) whereas aortic WSS is known to be a factor for aneurysm growth and other vessel degradation mechanisms (40)(41)(42)(43).…”