Introduction: Three-dimensional Phase-Contrast (4D Flow) MRI is a valid non-invasive technique to capture the temporal and complex 3D blood velocity field in the aortic root. Here, through advanced 4D Flow MRI processing, we quantified the aortic flow dynamics after valve sparing root replacement, comparing the effects of aortic grafts with or without recreation of the Valsalva sinuses on the neo-root postoperative fluid dynamics.
Methods: We enrolled patients submitted to valve sparing root replacement with a straight tubular prosthesis (n=8) or with a prosthesis with Valsalva neo-sinuses (n=8), also including 6 control subjects. 4D Flow MRI acquisitions were performed on a 3.0T MR unit in oblique-sagittal orientation to encompass the entire thoracic aorta. In-house processing was exploited to segment the aortic lumen, extract the 4D Flow velocity field and quantify bulk flow variables in the ascending and descending aorta. We computed flow velocity, regional wall shear stress (peak and mean WSS, axial and circumferential components), blood vorticity and local normalized helicity (LNH).
Results: Physiologic-like sinus vortices were clearly visible in the aortic root when using the prosthesis with Valsalva neo-sinuses while localized intrados malrotations were noticed using the straight tubular graft (Fig.1). Both the techniques reported a not negligible alteration (p<0.001) of aortic physiologic right-handed aortic helix. Recreation of the sinuses of Valsalva resulted in significantly lower wall shear stress (WSS) than the straight tubular graft, both in the proximal and distal aorta, as pointed out by mean WSS (p < 0.001) and the corresponding axial and circumferential components (Fig.2).
Conclusions:Recreation of the sinuses of Valsalva during valve sparing root replacement is associated with significantly lower WSSs in the aortic root. Lower WSSs in the distal thoracic aorta is a novel finding with potential implications on distal aortic remodeling.