Patients and Methods:
Patient 1 was a 66-year-old woman with TAV who presented with a 5.1 cm ascending aortic (AAo) aneurysm extending into a 4.3 cm transverse arch with moderate AI on echocardiography. She underwent AAo and proximal transverse arch replacement using a 24 mm Dacron graft and placement of a 21 mm HAART ring. Patient 2 was a 62-year-old woman with TAV who presented with an AAo aneurysm and mild-to-moderate AI on echocardiography. Preoperative cardiac MR demonstrated an aortic root diameter of 3.6 cm, an AAo diameter of 5.2 cm, and a proximal transverse arch diameter of 4.4 cm. The patient underwent AAo and transverse arch replacement with a 26 mm Dacron graft and placement of a 21 mm HAART ring. All patients provided informed consent and the study was approved by the Institutional Review Board of Northwestern University.
To understand the impact of aortic replacement and HAART ring implantation on aortic hemodynamics, 4D flow MRI was performed pre- and post-operatively in patient 1, and post-operatively in patient 2. Post-operative scans were acquired on post-op day 4 and day 2 for patients 1 and 2, respectively. Aortic hemodynamics were visualized using time-resolved 3D pathlines to illustrate blood flow over the cardiac cycle (EnSight, Ansys, USA). 3D velocity streamlines tangent to the time-resolved velocity vector field were used to demonstrate instantaneous hemodynamics in the aorta. All traces were color-coded according to velocity. Peak velocity, forward and retrograde flow, and regurgitant fraction were calculated within planes placed orthogonal to the aortic midline at the levels of the aortic root 1 cm above the AV, in the proximal AAo 1 cm above the sinotubular junction, in the mid AAo at the level of the pulmonary artery, in the AAo just proximal to the brachiocephalic trunk, between the brachiocephalic trunk and the left common carotid artery, between the left common carotid and left subclavian arteries, in the proximal descending aorta (DAo), in the mid DAo at the level of the aortic root, and in the distal DAo. 3D systolic wall shear stress (WSS) magnitude at the surface of the aorta, which has been implicated in aortic wall remodeling, was calculated at peak systole and maximal intensity plots were generated for the AAo and arch4. Peak viscous energy loss (VEL) over the cardiac cycle, a marker of abnormal flow and ventricular loading, was calculated and normalized to segmented aortic volume5. VEL and WSS in HAART patients were compared to an 80-year-old woman with TAV who underwent AAo and proximal transverse arch replacement without HAART ring placement as a control.