Blood flow characteristics in the ascending aorta after aortic valve replacement - A pilot study using 4D-flow MRI

Background Aortic remodeling after aortic valve replacement (AVR) might be influenced by the postoperative blood flow pattern in the ascending aorta. This pilot study used flow-sensitive four-dimensional magnetic resonance imaging (4D-flow) to describe ascending aortic flow characteristics after various types of AVR. Methods 4D-flow was acquired in 38 AVR patients (n = 9 mechanical, n = 8 stentless bioprosthesis, n = 14 stented bioprosthesis, n = 7 autograft) and 9 healthy controls. Analysis included grading of vortex and helix flow (0-3 point scale), assessment of systolic flow eccentricity (1-3 point scale), and quantification of the segmental distribution of peak systolic wall shear stress (WSS_peak) in the ascending aorta. Results Compared to controls, mechanical prostheses showed the most distinct vorticity (2.7 ± 0.5 vs. 0.7 ± 0.7; p < 0.001), while stented bioprostheses exhibited most distinct helicity (2.6 ± 0.7 vs. 1.6 ± 0.5; p = 0.002). Instead of a physiologic central flow, all stented, stentless and mechanical prostheses showed eccentric flow jets mainly directed towards the right-anterior aortic wall. Stented and stentless prostheses showed an asymmetric distribution of WSS_peak along the aortic circumference, with significantly increased local WSS_peak where the flow jet impinged on the aortic wall. Local WSS_peak was higher in stented (1.4 ± 0.7 N/m²) and stentless (1.3 ± 0.7 N/m²) compared to autografts (0.6 ± 0.2 N/m²; p = 0.005 and p = 0.008) and controls (0.7 ± 0.1 N/m²; p = 0.017 and p = 0.027). Autografts exhibited lower absolute WSS_peak than controls (0.4 ± 0.1 N/m ² vs. 0.7 ± 0.2 N/m²; p = 0.003). Conclusions Flow characteristics in the ascending aorta after AVR are different from native aortic valves and differ between various types of AVR.