Editorial for “Multiyear Interval Changes in Aortic Wall Shear Stress in Patients with Bicuspid Aortic Valve Assessed by 4D Flow MRI”

Bicuspid aortic valve (BAV) is the most common congenital heart disease consisting on partial or total fusion of two aortic valve leaflets.1 One of the main clinical consequences of BAV is the development of dilation of the aortic root or ascending aorta (AscAo), which frequently results in prophylactic intervention to prevent aortic dissection or rupture. Current clinical management of BAV aortopathy is grounded on reducing modifiable risk factors and on periodic imaging to assess the progression of aortic dilation. Nonetheless, several studies addressed the limitations of current management, especially with respect to the assessment of risk,2, 3 and thus of risk–benefit balance, that should be considered in the decision of prophylactic intervention. In the last years substantial efforts have been dedicated to research in aortopathy in BAV patients. Among the various approaches, the study of aortic flow with 3D, time-resolved phase contrast magnetic resonance imaging (MRI), often referred to 4D flow MRI, stood out. This image technique provides a time-resolved velocity field in the aorta, which can be manipulated to extract a comprehensive description of blood flow. Through several independent cross-sectional studies, a clear description of the abnormalities of aortic blood flow was created.1 These abnormalities include the misalignment between blood velocity and aortic main direction, the presence of vortical flow patterns, and blood motion-induced stress on the aortic wall, notably in terms of wall shear stress (WSS). Abnormalities in systolic WSS were shown to be associated with colocalized medial elastin degradation,4 decreased elastic aortic wall fiber thickness,5 and progressive dilation,6 while scan–rescan studies showed good reproducibility,7 positioning this biomarker as top priority for its introduction in clinical care. In the present issue of the Journal of Magnetic Resonance Imaging, Maroun et al8 presented evidence on the long-term longitudinal evolution of WSS in BAV patients. The study analyzed a multi-year follow-up of 20 patients, each of them having undergone five 4D flow MRI studies over a mean follow-up of 5.5 years. On each study, the authors measured the relative area of elevated WSS, meaning the percentage of AscAo wall where WSS was higher than the top 95% value of an age- and sex-matched group of 10 healthy individuals. One of the key results was that area of elevated WSS was relatively stable over such long-term follow-up, which sustains the robustness of WSS in patients with stable aortic diameter, an important aspect for serial measures in clinical practice and a good test of negative predictive value. If confirmed by other studies with larger cohorts, present results could be important for the implementation of 4D flow MRI in clinical practice. From one hand, the relative stability of areas of elevated WSS might permit to bypass 4D flow MRI in certain clinically indicated MRI scans of patients presenting limited growth, given that one WSS assessment every few years could be enough to represent the status of this biomarker over that period. On the other hand, present results should be extrapolated with caution to cases of patients developing fast dilation, particularly regarding 1) whether WSS may permit the early detection of such high-risk evolution and 2) whether this rapid dilation is accompanied by substantial changes in WSS profiles. Future research may consider these aspects to further consolidate WSS as imaging biomarker in BAV aortopathy. As a secondary result, the authors reported the relatively low reproducibility of serial assessment of diameter (low bias but 1 mm/year wide limits of agreement), which is especially problematic in case of serial assessment over a relatively short period. This highlight a previously known problem with substantial impact in everyday clinical practice,9, 10 which should receive much more attention from the community. For quantitative, precision medicine to be realized in aortic diseases, the reproducibility and sensitivity of the assessment of aortic diameter should be substantially improved. Dr Guala received funding from “la Caixa” Foundation (LCF/BQ/PR22/11920008).