Bicuspid aortic valve disease is associated with abnormal wall shear stress, viscous energy loss, and pressure drop within the ascending thoracic aorta

Abstract

Bicuspid aortic valve (BAV) disease has significant gaps in its clinical management practices. To highlight the potential utility of advanced hemodynamic biomarkers in strengthening BAV assessment, we used 4-dimentional flow magnetic resonance imaging to investigate altered hemodynamics in the ascending aorta (AAo). A total of 32 healthy controls and 53 age-matched BAV patients underwent cardiac magnetic resonance imaging at 3T, with cine imaging and 4D-flow. Analysis planes were placed along 3D-segmented aortas at the left ventricular outflow tract (LVOT), sinuses of Valsalva, mid-ascending aorta (MAA), and proximal to the first aortic branch. Locations were analyzed for aortic diameter (normalized to body surface area), pressure drop (PD), viscous energy loss (EL), and wall shear stress (WSS) sub-vectors (axial wall shear stress, circumferential wall shear stress [WSS C ], magnitude wall shear stress). Student's t tests, or non-parametric equivalents, compared parameters between cohorts. Univariable and multivariable analyses explored the associations of AAo diameter with hemodynamics within the BAV cohort. Compared to control cohort, BAV patients showed significantly greater PD (MAA: 9.5 ± 8.0 vs 2.8 ± 2.4 mm Hg; P < .01), EL (from LVOT-AA1: 7.39 ± 4.57 mW vs 2.90 ± 1.07 mW; P < .01), and WSS C (MAA: 0.3 ± 0.1 vs 0.2 ± 0.06 Pa; P ≤ .01) throughout the AAo. Correlational analyses revealed an inverse association between AAo diameter and both magnitude wall shear stress and axial wall shear stress. BAV patients exhibited increased PD, EL, and WSS C in the AAo, and an inverse association between AAo diameter and WSS sub-vectors. This demonstrated the impact of PD, EL, and WSS in BAV disease and the importance of altered hemodynamics in aortic remodelling.

4D-flow MRI derived wall shear stress for the risk stratification of bicuspid aortic valve aortopathy: A systematic review

“…BAV had higher reported sample mean WSS mag and WSS circ , and lower WSS ax than TAV, however, the difference in sample mean WSS ax between BAV and TAV was not statistically significant. Across studies, sample mean WSS circ was consistently reported higher in BAV than TAV regardless of the presence of aortic dilatation, BAV phenotypes or the aortic region where the measurements were taken (25,27,31,40,41).…”

Clinical implications of the biomechanics of bicuspid aortic valve and bicuspid aortopathy

“…BAV is associated with an increase in aortic wall shear stress (WSS) (74)(75)(76), the tangential shear force that blood flow exerts on a vessel wall, and thus potentially expression of aortopathy. Four-dimensional flow magnetic resonance imaging (4-D flow MRI) can be used to assess for WSS, the aortic valve, and the thoracic aorta (77).…”

“…Moreover, BAV is associated with a greater total pressure gradient along the aorta distal to the aortic valve and higher viscous energy loss compared to tricuspid valves. An increase in loss of both pressure and energy are known to be related to abnormal helical flow and aortic dilatation in BAV patients (Figure 3) (74,78). BAV also causes increased reverse flow and reduced stasis of blood (70).…”

Intra-cardiac pressure drop and flow distribution of bicuspid aortic valve disease in preserved ejection fraction

“…Lately, 4D-flow MRI, among various diagnostic techniques, has massively enhanced the understanding of multifaceted and pulsatile blood flow patterns within the heart and mediastinal vessels by uncovering and characterizing different flow parameters and advanced flow biomarkers ( 25 , 26 ). 4D flow MRI also offers a more robust and precise computation of temporally and spatially distributed pressure drop within the complex hemodynamic conditions of the region of interest with fewer assumptions than the other methods ( 24 , 27 , 28 ). However, MRI and the recently derived 4D flow technique have limitations that prevent them as the first line of diagnosing, ranging from pricy and cases with contraindication for MRI (patients with implanted pacemakers or defibrillator) to long scan time related to 4D flow MRI.…”

“…Integration of morphological data and 3D cine phase-contrast cardiovascular magnetic resonance (PC-CMR) flow data has allowed addressing unresolved physiological and clinical questions of BAV mediated hemodynamics on the surrounding environment such as LV and thoracic aorta clinically ( 30 – 32 ). However, BAV-induced regurgitation impairment on the left ventricle as a hardworking cardiac chamber during the cardiac cycle needs additional attention ( 33 ).…”