Impact of pulmonary artery flow distribution on Fontan hemodynamics and flow energetics

Background: With improved life expectancy following Fontan palliation, there is an increasing population of patients with a total cavopulmonary connection. However, there is a poor understanding of which patients will experience Fontan failure and when. 4D flow MRI has identified several metrics of clinical interest, but longitudinal studies investigating hemodynamics in Fontan patients are lacking. Objective: We aimed to investigate the relationship between flow distribution to the pulmonary arteries and regional hemodynamic metrics in a unique cohort with follow-up 4D flow MRI. Materials and methods: Patients with > 6 months of 4D flow MRI follow-up were included. Flow distribution from the caval veins to pulmonary arteries was measured in addition to regional measures of peak velocity, viscous energy loss (EL_mean and EL_tot), and kinetic energy. Results: Ten patients with total cavopulmonary connection (17.7 ± 8.8 years at baseline, follow-up: 4.4 ± 2.6 years) were included. Five subjects had unequal flow distribution from the IVC to the pulmonary arteries at baseline. Over time, these subjects tended to have larger increases in peak velocity (39.2% vs 6.6%), EL_mean (11.6% vs -38.3%), EL_tot (9.5% vs -36.2%), and kinetic energy (96.1% vs 36.3%) in the IVC. However, these differences were statistically insignificant. We found that changes in EL_mean and EL_tot were significantly associated with changes in peak velocity in the caval veins (R² > 0.5, P < 0.001). Conclusion: Unequal flow distribution from the IVC may drive increasing peak velocities and viscous energy losses, which have been associated with worse clinical outcomes. Changes in peak velocity may serve as a surrogate measure for changes in viscous energy loss.