Post-stenotic dilation: Evaluation of ascending aortic dilation with 4D flow MR imaging

Abstract

Post-stenotic aortic dilation is a long-observed phenomenon that has been linked to elevatedmechanical stress on thewall of the ascending aorta caused by flow disturbance downstream of a stenotic lesion [1]. Uniquely detailed visualization of flow in the ascending aorta is possible with MR blood flow imaging using three-dimensional (3D), cine phase-contrast sequences, or 4D flow. The technique can also be used to estimate thewall shear stress experienced by vascular endothelium [2]. We have used 4D flow to characterize abnormal systolic flow and shear stress in a number of patients with post-stenotic aortic dilation. Normal systolic flow in the ascending aorta is laminar, with fastest flow in the vessel center, and shear stress evenly distributed around the aortic circumference (Fig. 1A). In patients with post-stenotic dilation, however, systolic flow is eccentric, displaced from the centerline toward the vessel wall, and follows a helical path through the ascending aorta. Consequently, wall shear stress is asymmetrically elevated. This altered fluid-mechanical environment in the ascending aorta is seen with both stenotic tricuspid and bicuspid aortic valves (TAV and BAV; Fig. 1B, C). Elevated wall shear stress, particularly positive shear stress