Abstract Body (Do not enter title and authors here): Introduction
Pulmonary regurgitation and ensuing volume load in repaired tetralogy of Fallot (rTOF) leads to remodeling of the right ventricle (RV) and which has been associated with adverse long-term outcomes. Pulmonary valve replacement (PVR) is associated with variable degrees of RV reverse remodeling. There is evidence that earlier age at PVR is associated with improved clinical outcomes.

Research Question / Hypothesis
The aim was to determine whether age at PVR was associated with the degree of RV reverse remodeling in rTOF. We hypothesized that younger age at PVR would enable a greater degree of RV reverse remodeling.

Materials and Methods
Retrospective single-center cohort study of rTOF patients from the SCOUT-TOF registry (Single Center Outcomes study using CMR – Tetralogy of Fallot) who underwent PVR for an indication of RV dilation and had cardiac magnetic resonance imaging (CMR) performed before and after PVR. Multivariable linear regression assessed the association of age at PVR with percent change of indexed RV end-diastolic volume (RVEDVi) and end-systolic volume (RVESVi) from pre-to post-PVR CMR, adjusted for time since PVR, surgical PVR (vs. transcatheter), sex, and presence of a pulmonary artery stent prior to PVR. For patients with multiple post-PVR CMR studies, the study with the lowest RVEDVi and RVESVi was used.

Results
In total, 105 patients with rTOF were included, 71 (68%) were male. PVR dates ranged from 2005 to 2020. PVR was performed at median age 20 years (IQR 16, 28), with CMR 3.8 years (IQR 1.7, 5.7) post-PVR, with median age at CMR of 30.6 years (IQR). RVEDVi percent change from pre- to post-PVR measurement was -37% (IQR -46, -27) and RVESVi percent change was -38% (IQR -48, -21).

There was no association between age at PVR and percent change in RVEDVi with an estimated mean percent change 0.09% (95% CI -0.28,0.47, p = 0.62) nor between age at PVR and percent change in RVESVi on adjusted models.

Conclusion
In this retrospective study we did not observe an age advantage to volume-based RV reverse remodeling after PVR. Further study to determine whether timing of PVR impacts clinical outcomes and the role of reverse RV remodeling on outcomes is warranted.