Discordance between 2D and 4D flow in the assessment of pulmonary regurgitation severity: a right ventricular remodeling follow-up study.

OBJECTIVES: Pulmonary regurgitation (PR) is common in adult congenital heart disease (ACHD). 2D phase contrast MRI is the reference method for the quantification of PR and helps in the decision of pulmonary valve replacement (PVR). 4D flow MRI can be an alternative method to estimate PR but more validation is still needed. Our purpose was to compare 2D and 4D flow in PR quantification using the degree of right ventricular remodeling after PVR as the reference standard. METHODS: In 30 adult patients with a pulmonary valve disease recruited between 2015 and 2018, PR was assessed using both 2D and 4D flow. Based on the clinical standard of care, 22 underwent PVR. The pre PVR estimate of PR was compared using the post-operative decrease in right ventricle end-diastolic volume on follow-up exam as reference. RESULTS: In the overall cohort, regurgitant volume (Rvol) and regurgitant fraction (RF) of PR measured by 2D and 4D flow were well correlated but with moderate agreement in the overall cohort (r = 0.90, mean diff. -14 ± 12.5 mL; and r = 0.72, mean diff. -15 ± 13%; all p < 0.0001). Correlations between Rvol estimates and right ventricle end-diastolic volume decrease after PVR was higher with 4D flow (r = 0.80, p < 0.0001) than with 2D flow (r = 0.72, p < 0.0001). CONCLUSIONS: In ACHD, PR quantification from 4D flow better predicts post-PVR right ventricle remodeling than that from 2D flow. Further studies are needed to evaluate the added value of this 4D flow quantification for guiding replacement decision. KEY POINTS: • Using 4D flow MRI allows a better quantification of pulmonary regurgitation in adult congenital heart disease than 2D flow when taking right ventricle remodeling after pulmonary valve replacement as a reference. • A plane positioned perpendicular to the ejected flow volume as allowed by 4D flow provides better results to estimate pulmonary regurgitation.