Progressive ascending aortic dilatation has been observed after mechanical aortic valve replacement (mAVR), possibly due to altered blood flow and wall shear stress (WSS) patterns induced by their bileaflet design. We examined the effect of mAVR on WSS in the ascending aorta using time-resolved 4D flow MRI. Fifteen patients with mechanical aortic valve prostheses, 10 patients with bicuspid aortic valve disease and 10 healthy individuals underwent thoracic 4D flow MRI. Peak systolic hemodynamic parameters (velocity and WSS) and vessel diameters were assessed in the ascending aorta. In addition, three-dimensional per-voxel analysis was used to compare velocity and WSS between patient groups and healthy controls. Peak aortic diameters were significantly higher in mAVR and BAV patients compared to healthy controls (p = 0.011). Mean aortic diameters were comparable between mAVR and BAV patients. No differences in 4D flow MRI-derived mean blood flow velocity and peak WSS were found between the three groups. Compared to healthy controls, mean WSS was significantly lower in mAVR patients (p = 0.031). Per-voxel analysis revealed no increased WSS in the ascending aortic wall and significantly lower velocity and WSS values in mAVR patients compared to healthy controls. In contrast, regions of significantly increased outer lumen velocities and WSS in BAV patients compared to healthy controls were found. This study shows that there is no increased ascending aortic WSS after mAVR. Our results suggest that, in contrast to BAV patients, there is no indication for intensified follow-up of the ascending aorta after mAVR.
Keywords: 4D flow MRI; Aortic valve prosthesis; Magnetic resonance imaging; Mechanical aortic valve; Wall shear stress.