Abnormal Blood Flow Dynamics Assessed with 4D Flow MRI Are Associated with Shape and Torsion of the Reconstructed Aortic Arch in Patients with Hypoplastic Left Heart Syndrome after Palliation

Objectives: The reconstructed aortic arch of patients with hypoplastic left heart syndrome (HLHS) has an important impact for long-term prognosis. Four-dimensional (4D)-flow magnetic resonance imaging (MRI) allows determining a variety of novel fluid dynamic parameters (e.g., helical blood flow pattern and vorticity in defined volumes of the vessel). Therefore, we thought to test the hypothesis that the abnormal aortic arch geometry after the Norwood operation affects blood flow dynamics and secondary, also right ventricular function and geometry.

Methods: Twenty-three HLHS patients (median age: 4.5; 2–17 years; all NYHA I) underwent comprehensive MRI examinations including 4D-flow acquisitions 1.8 (0.4–14.1) years after completion of the Fontan circulation. Volumetric data were used to estimate right ventricular (RV) function. With an in-house analysis software (C++ based), novel parameters of blood flow dynamics were calculated within the cardiac cycle along the entire thoracic aorta from the neoaortic valve toward diaphragm and were correlated with geometric parameters (such as geometric torsion which describes the abnormal twisting of the aortic arch)

Results: Peak effective torsion (geometric torsion multiplied with curvature) of the neoaortic root correlated significantly with peak helicity density of the blood flow (p < 0.01, adj. R2 = 0.33, rho = 0.59). The peak helical blood flow (expressed as helicity density) showed a significant correlation with diameter changes along the aorta (p = 0.03, adj. R2 = 0.18, rho = 0.46) as well as with the maximum diameter of the aorta (p = 0.04, adj. R2 = 0.15, rho = 0.44). While RV functions (EF 57% ± 10%), volumes and mass did not correlate with any of the flow parameters, the mass-to-volume ratio, a parameter of eccentric geometric remodeling of the RV, correlated inversely with the peak helicity density (p = 0.05, adj. R2 = 0.14, rho = −0.43).

Conclusion: Our data show that abnormal blood flow patterns in the reconstructed aortic arch in HLHS after three-stage palliation are strongly associated with abnormal geometric torsion of the arch, aortic diameter differences, and eccentric RV shape. Our findings may trigger modifications of surgical aortic arch reconstruction to optimize fluid-dynamic conditions in future patients.