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

Abstract

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 (ELmean and ELtot), 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%), ELmean (11.6% vs -38.3%), ELtot (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 ELmean and ELtot 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.

Characterization of baseline hemodynamics after the Fontan procedure: a retrospective cohort study on the comparison of 4D Flow MRI and computational fluid dynamics

“…Quantification of PFD is crucial in the treatment of Fontan circulation since hepatic flow distribution has been found to be associated with the development of pulmonary arteriovenous malformations ( Yang et al, 2012 ; Bächler et al, 2013 ). The quantification of PFD can be accomplished using two methods: the flow rate calculation method ( Tang et al, 2014 ; Frieberg et al, 2022 ) and the calculation method using particle trace ( Bächler et al, 2013 ; Ha et al, 2019 ; Weiss et al, 2023 ). We found a strong correlation (r = 0.71) between 4D Flow MRI and CFD for PFD from the SVC, while a moderate correlation (r = 0.40) was observed for PFD from the conduit.…”

“… 2. VD (per unit volume) ( Cibis et al, 2015 ; Wei et al, 2017 ; Weiss et al, 2023 ): Where denotes the dynamic viscosity, is the time-averaged velocity component of the fluid (either x, y, or z directions), is the viscous dissipation per voxel volume or cell volume, is the number of voxels or cells within the field of view. 3.…”

“… 3. Pulmonary flow distribution (PFD) from the SVC or conduit to the LPA or RPA ( Figures 2A, B ) ( Bächler et al, 2013 ; Ha et al, 2019 ; Weiss et al, 2023 ): Where is the number of traces from A to B.…”

“…4D Flow MRI enables the quantification of hemodynamic parameters such as kinetic energy (KE), pulmonary flow distribution (PFD), and energy loss which can aid in understanding the hemodynamics of Fontan circulation ( van der Woude et al, 2021 ; Rijnberg et al, 2022a ; Weiss et al, 2023 ). Furthermore, 4D Flow MRI has been used to identify the correlations between hemodynamic energetics and clinical outcomes in Fontan circulation ( Kamphuis et al, 2019 ; Kamphuis et al, 2021 ; Rijnberg et al, 2022b ).…”

“…Efficient blood flow distribution is especially critical for infants immediately after undergoing the Fontan procedure. However, most studies have been conducted on a wide age range of patients, from childhood to adulthood ( Haggerty et al, 2014 ; Khiabani et al, 2014 ; McLennan et al, 2019 ; Rijnberg et al, 2021 ; Frieberg et al, 2022 ; Weiss et al, 2023 ), and there is a lack of baseline characterizations of infants and their correlation to follow-up results.…”