Aortic flow patterns and wall shear stress maps by 4D-flow cardiovascular magnetic resonance in the assessment of aortic dilatation in bicuspid aortic valve disease

Abstract

BackgroundIn patients with bicuspid valve (BAV), ascending aorta (AAo) dilatation may be caused by altered flow patterns and wall shear stress (WSS). These differences may explain different aortic dilatation morphotypes. Using 4D-flow cardiovascular magnetic resonance (CMR), we aimed to analyze differences in flow patterns and regional axial and circumferential WSS maps between BAV phenotypes and their correlation with ascending aorta dilatation morphotype.MethodsOne hundred and one BAV patients (aortic diameter ≤ 45 mm, no severe valvular disease) and 20 healthy subjects were studied by 4D-flow CMR. Peak velocity, flow jet angle, flow displacement, in-plane rotational flow (IRF) and systolic flow reversal ratio (SFRR) were assessed at different levels of the AAo. Peak-systolic axial and circumferential regional WSS maps were also estimated. Unadjusted and multivariable adjusted linear regression analyses were used to identify independent correlates of aortic root or ascending dilatation. Age, sex, valve morphotype, body surface area, flow derived variables and WSS components were included in the multivariable models.ResultsThe AAo was non-dilated in 24 BAV patients and dilated in 77 (root morphotype in 11 and ascending in 66). BAV phenotype was right-left (RL-) in 78 patients and right-non-coronary (RN-) in 23. Both BAV phenotypes presented different outflow jet direction and velocity profiles that matched the location of maximum systolic axial WSS. RL-BAV velocity profiles and maximum axial WSS were homogeneously distributed right-anteriorly, however, RN-BAV showed higher variable profiles with a main proximal-posterior distribution shifting anteriorly at mid-distal AAo. Compared to controls, BAV patients presented similar WSS magnitude at proximal, mid and distal AAo (p = 0.764, 0.516 and 0.053, respectively) but lower axial and higher circumferential WSS components (p < 0.001 for both, at all aortic levels). Among BAV patients, RN-BAV presented higher IRF at all levels (p = 0.024 proximal, 0.046 mid and 0.002 distal AAo) and higher circumferential WSS at mid and distal AAo (p = 0.038 and 0.046, respectively) than RL-BAV. However, axial WSS was higher in RL-BAV compared to RN-BAV at proximal and mid AAo (p = 0.046, 0.019, respectively). Displacement and axial WSS were independently associated with the root-morphotype, and circumferential WSS and SFRR with the ascending-morphotype.ConclusionsDifferent BAV-phenotypes present different flow patterns with an anterior distribution in RL-BAV, whereas, RN-BAV patients present a predominant posterior outflow jet at the sinotubular junction that shifts to anterior or right anterior in mid and distal AAo. Thus, RL-BAV patients present a higher axial WSS at the aortic root while RN-BAV present a higher circumferential WSS in mid and distal AAo. These results may explain different AAo dilatation morphotypes in the BAV population.Electronic supplementary materialThe online version of this article (10.1186/s12968-018-0451-1) contains supplementary material, which is availab...

Elevated diastolic wall shear stress in regurgitant semilunar valvular lesions

“…Elevated WSS in BAV has been previously reported . The presence of aortic stenosis was associated with a further increase in WSS .…”

“…Finally, no patients with severe aortic regurgitation were present in the study population. In addition, the cusp fusion type was not described, as the effect of cusp fusion type has been previously investigated …”

“…In valvular heart disease, WSS has been extensively studied in bicuspid aortic valve (BAV), and was shown to correlate with pathological changes in the aorta . The presence of aortic stenosis was associated with further increases in WSS .…”

Familial clustering of bicuspid aortic valve and its relationship with aortic dilation in first-degree relatives

“…This interesting finding may widen our understanding of aortic dilation in FDR but should be interpreted with caution, as this was not the aim of our study. We hypothesise that these mini-raphes may disturb ascending aorta flow in a similar way to BAV24 (see figure 2). In a recent publication, surgical inspection of aortic valves in the setting of thoracic aneurysm and aortic insufficiency found very small raphes (ie, 3–6 mm in length) in valves initially considered to be tri-leaflet.…”

Aorta flow characteristics may provide key information to understand the aorta dilation in bicuspid aortic valve

“…This different phenotype of ascending aorta dilation with dilation in different segments, that is, aortic root, tubular part or aortic arch, may be explained by the eccentric flow, different jet direction, helical flow and wall shear stress of each BAV morphotype. In a recent study,2 our group proved that BAV-RL had an increase in in-plane rotational flow and axial wall shear stress at the aortic root and ascending aorta with an anterior distribution; by contrast, BAV-RN showed an increase in in-plane rotational flow and circumferential wall shear stress at the distal ascending aorta and proximal aortic arch. Characteristically, patients with aortic root dilation phenotype were younger, more likely to be men, had increased aortic regurgitation frequency but low aortic stenosis frequency and BAV-RN morphotype 3.…”