Comparison of 2D and 4D Flow MRI Measurements for Hemodynamic Evaluation of the Fontan Palliation

Background:The assessment of Fontan circuit’sflow is traditionally evaluated by multiple through-plane phase-contrast MRI acquisitions(2Dflow),while recently,a single volumetric 4D-flow MRI acquisition is emerging as a comprehensive tool for the hemodynamic evaluation in congenital heart diseases.Purpose:To compare 2D and 4D-flow MRI measurements in patients after Fontan palliation and to evaluate parameters affecting potential dis-agreement.Methods:39 patients after Fontan palliation(23 males,age 22±11 years)who underwent cardiac MRI with 2D and 4D-flow MRI acquisition were included in the study.In all patients,bloodflow quantification in the Fontan circuit and aorta by 2Dflow and by 4Dflow MRI acquisition blinding to the 2D results was per-formed.The agreement between 2D and 4D-flow MRI was calculated as the intraclass correlation coefficient(ICC).The mean absolute differences between 4D and 2Dflows were analyzed using linear regression models.Results:4D-flow MRI acquisition time was slightly lower than 2D(7.6±1.8 min vs.9.4±3.3 min,p=0.03).Flow was slightly predominant in the right pulmonary artery(58%of total pulmonaryflow).Conduit/tunnel-pul-monary arteriesflow accounted for 60%of the Fontan circuit.Agreement between 2D and 4D was overall good-to-excellent from ICC:0.81795%CI:0.637–0.907 to 0.93295%CI:0.866–0.965.There was no significant influ-ence of evaluated parameters on the agreement on 4D and 2Dflow.Conclusions:4D-flow MRI represents a valid tool in Fontan’sflow quantification.Further larger studies are needed to confirm our results and to evaluate the impact of advanced 4D-flow MRI parameters on the prognostic stratification in patients after Fontan palliation.

Pulmonary Perfusion Asymmetry in Patients after Repair of Tetralogy of Fallot: A 4D Flow MRI-Based Study

Background:Repaired Tetralogy of Fallot(rTOF)patients may have residual lesions such as main(MPA)and branch pulmonary artery stenosis(BPAS).While MPA stenosis is well studied,few data are available on BPAS in rTOF.We aimed to describe pulmonary perfusion in a large paediatric cohort of rTOF and its impact on right ventricular and outflow-tract hemodynamics using 4D flow CMR.Methods:130 consecutive patients(mean age at CMR 14.3±4.6 years)were retrospectively reviewed.96 patients had transannular patch without valve preservation while 34 patients had conserved annulus or valved conduit.A pulmonary blood flow ratio(right pulmonary artery(RPA)/left pulmonary artery(LPA))between 0.75 and 1.56 was considered normal.Results:Asymmetric pulmonary perfusion was present in 59/130 patients(45%),with 54/59(91%)having left lung hypoperfusion(blood flow ratio>1.56).RPA/LPA perfusion ratio in the whole cohort was independently associated with the LPA Z-score(−0.053,p=0.007),the RPA regurgitant fraction(RF)(0.013,p=0.011)and previous LPA stenting(0.648,p=0.004).Decreasing LPA%perfusion(and conversely increasing RPA%perfusion)was significantly associated with higher MPA diameter Z-score(−0.06,p=0.007).On multivariate analysis,MPA Z-score was independently associated with pulmonary RF(0.48,p<0.001)and with right ventricular indexed volumes(coefficient 3.6,p=0.023).In patients with transannular patch repair,asymmetric pulmonary flow was an independent predictor of right ventricular ejection fraction(RVEF)(−3.66,p=0.04).Conclusions:Pulmonary perfusion asymmetry is frequent in rTOF and is associated with abnormal right ventricular and outflow-tract hemodynamics,including MPA dilatation and decreased RVEF in patients after transannular patch.