Abstract 4352481: Four-Dimensional Flow Magnetic Resonance Imaging-Derived Vortex Flow and Wall Shear Stress Predict Short-Term Aortic Expansion in Ulcer-Like Projections of Aortic Dissection

Abstract

Background: Ulcer-like projections (ULPs) in aortic dissections are linked with aortic expansion, but predicting the progression is difficult. While earlier studies used computational fluid dynamics, 4D flow MRI allows direct in vivo measurement and visualization of complex blood flow dynamics. Hypothesis: We hypothesized that specific intra-ULP flow patterns, including vortex flow and wall shear stress (WSS) elevation, directly measured by 4D flow MRI, may predict short-term aortic expansion. Methods: We prospectively examined patients with ULP-type aortic dissection. Using 4D flow MRI, we assessed the intra-ULP hemodynamics, obtaining direct in vivo measurements of time-resolved 3D blood flow velocities. The intra-ULP vortex flow was detected using streamlines. WSS distribution on the ULP wall was analyzed, with localized WSS elevation as a key parameter. Patients were followed-up with serial CT or 4D flow MRI to monitor the aortic diameter. The primary endpoint was aortic expansion. Results: Nine patients with ULPs (mean age: 62.4 ± 10.8 years; 77.8% male;)—six with type A dissection and three with type B dissection—were analyzed. Four patients (44.4%; one with type A dissection and three with type B dissection) had vortex flow within the ULP and associated localized WSS elevation. All four patients showed rapid aortic expansion (mean increase: 7.25 ± 1.71 mm) between onset and follow-up CT/MRI over a short period (mean: 4.0 ± 5.4 months; median [range]: 1.5 [1-2] months). Three patients subsequently received thoracic endovascular aortic repair and one underwent total arch replacement. The remaining five patients (55.6%; all with Type A dissection) with no vortex flow and no remarkably localized WSS elevation within the ULP showed no significant aortic expansion (mean increase: 3.0 ± 1.58 mm) over a long period (mean: 41.0 ± 25.0 months; median [range]: 55 [3-61] months); all were managed conservatively. Intra-ULP vortex flow with localized WSS elevation based on direct flow measurements was significantly associated with short-term aortic expansion (p<0.05). Conclusion: Vortex flow within ULPs and localized WSS elevation, directly measured and visualized using 4D flow MRI, are strong predictors of short-term aortic expansion in patients with ULP-type aortic dissection.