Aortic hemodynamics in patients with and without repair of aortic coarctation: In vivo analysis by 4D Flow-sensitive magnetic resonance imaging

Objectives: The purpose of this study was to characterize hemodynamic alterations and flow-derived vessel wall parameters in aortic coarctation (CoA) patients with and without operative repair by time-resolved, 3-dimensional, and 3-directional velocity sensitive, phase-contrast magnetic resonance imaging (4D PC MRI) in comparison with healthy subjects. Methods and material: Twenty-four patients, 12.5 ± 6.4 years after CoA repair, 4 patients without treatment for CoA, and 19 healthy subjects were examined. The study was approved by the institutional review board and signature of written informed consent was obtained from the participants. Echocardiography was performed in patients before participation. MRI studies were conducted by applying flow-sensitive 4D phase-contrast MRI at either 1.5 T (n = 5 patients) or 3 T (all 19 healthy subjects, n = 23 patients). Blood flow visualization was used to evaluate overall aortic helicity, presence of pronounced or additional localized helix flow, and vortex development. Quantitative evaluation comprised the calculation of regional time-averaged absolute wall shear stress (WSSmag), peak velocities, and oscillatory shear index at 8 locations distributed along the thoracic aorta and additionally at the site of CoA. Inter- and intraobserver variabilities of calculations were determined. Results: Volunteers and patients demonstrated the same amount of overall aortic helicity. In contrast, the number of additional localized helix flow or vortex formation was significantly increased in patients (25/28 patients vs. 5/19 normal controls, Fisher exact test: P < 0.001). Vortices in the orifices of the supra-aortic branches were detected in 64.3% (18/28) of patients but in only 11.8% (2/19) of controls (P < 0.001). Quantitative analyses revealed a significant increase in overall aortic WSS _mag (0.44 ± 0.17 N/m²² in patients vs. 0.27 ± 0.08 N/m² in volunteers, P < 0.005) and a decrease in overall oscillatory shear index. Repeated quantitative analysis showed moderate interobserver and low intraobserver variability. Correlation with echocardiography showed good agreement with MRI which tended to underestimate peak velocities (r = 0.76; Bland-Altman analysis, limits of agreement = -0.57-2.16 m/s, mean = 0.79 m/s). Conclusion: Alterations in aortic hemodynamics after CoA repair are not limited to the specific region of repair, but can be found in the entire aorta. The presented findings highlight the systemic nature of the disease and the need for a systemic diagnostic approach which can be provided by flow-sensitive 4D PC MRI. Furthermore, valuable additional insights on the hemodynamic consequences of coarctation have been shown that may help understanding secondary complications such as restenosis, aneurysm formation, and arterial hypertension.