Portal vein 4D-flow dynamic evaluation in Fontan circulation

Background: In Fontan-associated liver disease (FALD), histological fibrosis is often not accurately reflected due to the influence of portal pressure. The objective ofthis study was to develop new indicators for evaluating FALD using portal vein hemodynamic analysis with 4D-flow MRI.

Methods: After obtaining approval from the institutional ethics committee at Sakakibara Heart Institute in Japan, we performed 4D-flow MRIimaging of the main portal vein in post-Fontan patients and healthy subjects. We measured kinetic energy (KE; unit: mJ/mL), energy loss (EL; unit: mW/mL), wallshear stress (WSS; unit: Pa), and helicity (unit: m⁴/s²). KE and EL were normalized by dividing by the main portal vein lumen volume. Helicity was defined as thevector quantity of clockwise and counterclockwise spirals and calculated as a sum. All parameters were averaged over one cardiac cycle to evaluate portal veinhemodynamics after Fontan surgery. The 4D-flow analysis was performed using iTFlow 3.3 (Cardio Flow Design, Japan).

Results: 4D-flow MRI of the main portal vein was performed in 15 post-Fontan patients (Group F; 19.3±6.4 years, 9 males) and 5 healthy subjects (Group N;35.0±7.0 years, 5 males). Diagnoses in Group F included double-outlet right ventricle (4 cases), pulmonary atresia with intact ventricular septum (4 cases),Ebstein anomaly (2 cases), and one case each of single left ventricle, single right ventricle, tricuspid atresia, transposition of great arteries, and atrio-ventricularseptal defect. All Fontan procedures were total cavopulmonary connections without fenestration. Catheter examinations were performed concurrently in 13cases, with a mean central venous pressure (CVP) of 11.6±4.4 mmHg. KE was significantly higher in Group N (F vs. N; 3.08E-03±1.22E-03 vs. 4.38E-03±4.50E-03,p< 0.05), while WSS was significantly higher in Group F (F vs. N; 1.34±0.27 vs. 1.04±0.26, p< 0.05). EL was higher in Group F and helicity was higher in Group N,but these differences were not statistically significant. In terms of helicity, counterclockwise spiral flow was predominant in both groups. KE showed correlationwith EL (r=0.69) and WSS (r=0.75), and EL demonstrated a weak correlation with CVP (r=0.56).

Conclusion: Despite the limited number of healthy subjects, this study revealed that portal blood flow in post-Fontan patients exhibits higher WSS, lower KE,and reduced spiral flow compared to healthy subjects. We plan to increase the number of cases for more detailed analysis and establish the utility of portal 4D-flow MRI in evaluating FALD.

portal vein 4D-flow