4D flow yields similar clinical results compared to 2D phase contrast for decision making regarding pulmonary valve replacement in repaired tetralogy of Fallot.

2D CMR is critical for monitoring PR fraction (PRF) and biventricular size in patients with a history of repaired tetralogy of Fallot and guides decisions about pulmonary valve replacement (PVR). However, its clinical utility is limited, increasing enthusiasm for newer techniques such as 3D time-resolved phase contrast (4D flow) MRI. We investigated whether using 4D flow to calculate PRF would yield similar clinical decisions about PVR in rTOF compared to conventional 2D CMR. All patients with rTOF who underwent standard CMR plus retrospectively gated 4D flow between February 2021 - June 2023 were identified. Clinical information was collected from the EMR. 2D cine SSFP, phase contrast (PC) data, and 4D flow imaging data were analyzed using standard post-processing analysis. Clinical decisions ("intervention vs. no intervention") were determined using a standardized algorithm, and inter-rater agreement was assessed using the coefficient. 33 patients were included. PRF correlated strongly between 2D PC and 4D flow (r=0.83) and with PRF determined by stroke volume (r=0.70). The mean absolute difference between 2D and 4D PRF was -3.4% (± 9.3%). Inter-rater agreement for the decision was moderate (=0.58) using only 2D PC and 4D flow, and was strong (=0.76) when using 2D PC with SV and 4D flow with SV. Though clinical indications for PVR in rTOF vary, 4D flow generates accurate measurements of PRF and yields similar clinical decisions about intervention in rTOF. Further study of ventricular volume assessment by 4D flow adoption could lead to a shorter, more comprehensive CMR exam for TOF patients.