Characterizing growth and early hemodynamic inefficiencies: Phase-contrast magnetic resonance imaging analysis of the aorta in post-Fontan hypoplastic left heart syndrome.

OBJECTIVE: To address the lack of routine hemodynamic assessment during aortic reconstruction in patients with hypoplastic left heart syndrome (HLHS) with a momentum-based metric from phase-contrast magnetic resonance imaging (MRI) data (4D Flow). METHODS: 4D Flow data were acquired in 100 subjects, including 22 Post-Fontan HLHS subjects (15 children, mean age 8.0 ± 1.7 years and 7 adolescents, mean age 15.1 ± 1.9 years) and 78 control subjects (mean age 7.6 ± 1.0 years). Comparative anatomic and functional analyses were performed in 4 segments: ascending aorta (AA), transverse arch (TA), and proximal and distal descending aortas (DA1 and DA2). Aortic growth was evaluated by its diameter indexed by body surface area, and early energy inefficiency was assessed by the advective pressure drop (PDA). RESULTS: Post-Fontan HLHS children presented with early hemodynamic inefficiency at the TA-DA1 transition (median PDA increment 81% larger in HLHS children than in controls; P = .01). The inefficiency in this region was further increased in the adolescent group (by an increment of 74% compared to the HLHS children; P = .022) despite the absence of anatomic obstruction and an average growth trajectory in line with that of controls. CONCLUSIONS: Early hemodynamic inefficiencies in the TA-DA1 transition in the HLHS aorta have been characterized. The PDA metric allows for a noninvasive and robust characterization of inefficiencies with distinctive spatial and amplitude precision. Further studies will improve our understanding of the association between PDA and outcomes.