Ascending aortic length is associated with increased wall shear stress and flow displacement

Background Ascending aortic diameter is traditionally used to guide clinical decision-making in patients with thoracic aortic dilatation; however, ascending aortic length (AAL) has recently emerged as an additional risk marker for adverse aortic events. Purpose The aim of this study was to investigate the association between ascending aortic length and aortic hemodynamics assessed by four-dimensional flow magnetic resonance imaging (4D flow MRI), focusing on wall shear stress (WSS) and flow displacement (FD). Methods This retrospective study included 59 patients undergoing preoperative 4D flow MRI prior to ascending aortic graft surgery for aortic dilatation. Ascending aortic length and aortic diameters were measured from anatomical MRI. Hemodynamic parameters, including maximal, axial, and circumferential WSS as well as FD, were quantified at predefined planes along the thoracic aorta. Patients were stratified according to AAL (≥11 cm vs. <11 cm) and valve morphology (bicuspid vs. tricuspid aortic valve). Associations between hemodynamic parameters, AAL, blood pressure, and clinical characteristics were analyzed. Results Patients with an AAL ≥11 cm demonstrated significantly higher WSS and FD compared with patients with shorter ascending aortas. These hemodynamic alterations were more evident in patients with bicuspid aortic valve than in those with tricuspid valves. Ascending aortic length, adjusted for valve type and sex, was positively associated with mid-tubular FD. In contrast, WSS was associated with systolic blood pressure at the aortic root, independent of valve type. Age, height, and weight showed no significant associations with WSS or FD. Conclusions Increased ascending aortic length is associated with altered aortic hemodynamics, particularly elevated WSS and FD, with more pronounced changes observed in patients with bicuspid aortic valve. These findings suggest that ascending aortic length may provide complementary information for assessment in patients with aortic dilatation.