Changes of Wall Shear Stress after Congenital Aortic Valve Repair Measured by 4D Flow Cardiovascular Magnetic Resonance Imaging

Objectives: Bicuspid aortic valves (BAV) are known to be associated with aortic valve dysfunction and proximal aortic dilatation. Quantification of transvalvular flow parameters measured by 4D flow MRI have been proposed to correlate with the aortopathy severity of the proximal aorta. However, the impact of aortic valve repair on transvalvular flow patterns and wall shear stress (WSS) distribution has not been evaluated. Herewith we aimed to analyze the impact of different aortic valve repair techniques on the WSS distribution before versus after aortic valve (AV) sparing surgery in congenital AV disease.

Methods: Four-dimensional (4D) flow MRI examination was performed prospectively before and after aortic valve repair in 20 consecutive BAV patients. The following MRI-based measurements were performed: (1) WSS analysis (N/m²) of the thoracic aorta, (2) grading of flow changes (i.e., vortical and helical flow), and (3) regurgitant fraction (%) across the aortic valve. MRI measurements were compared between two subgroups according to the predominant aortic valve pathology (AV-prolapse [n = 13] and AV-restriction [n = 7]).

Results: Mean age of the studied cohort was 38.7 ± 11.9 years and 80% were male. BAV was present in 16 patients and UAV in 4 patients. There were no significant differences in the baseline variables between both subgroups. All patients in the AV-prolapse group presented with prolapse of the fused cusp and annular dilatation (mean annular size of 30.9 ± 2.48 mm). AV repair was performed by central plication sutures and suture annuloplasty to reduce the AV annulus to £25 mm. The AV-restriction group was mainly treated with pericardial patch material (n = 5). Postoperative WSS was significantly reduced in the AV-prolapse group in the ascending aorta (preoperative: 0.764 ± 0.247; postoperative: 0.544 ± 0.166 N/m²; p = 0.008), as well as in the aortic arch (preoperative: 0.865 ± 0.396; postoperative: 0.503 ± 0.205 N/m²; p = 0.003). Further there was a postoperative reduction in the flow vorticity in the AV-prolapse subgroup (grades 2–0). In the AV-restriction group, there were no significant changes in WSS in the ascending aorta (preoperative: 0.795 ± 0.273; postoperative: 0.524 ± 0.196 N/m²; p = 0.099), as well as in the aortic arch (preoperative: 0.703 ± 0.223; postoperative: 0.581 ± 0.259 N/m²; p = 0.278).

Conclusion: AV repair in BAV prolapse results in significant normalization of transvalvular flow patterns and reduction of wall shear stress in the proximal aorta. However, the impact of wall shear stress reduction on the long-term outcome after AV repair needs to be further evaluated.