Donor Right Ventricular Oversizing Is Independently Associated With Severe Primary Graft Dysfunction After Heart Transplantation: A Multicenter Retrospective Analysis.

BACKGROUND: Predicted heart mass (PHM) is widely used for donor-recipient size matching in heart transplantation, yet its relevance to early graft performance in the modern allocation era remains uncertain. Emerging data suggest that left and right ventricular mismatch may exert distinct physiologic effects that are obscured by total PHM. METHODS: We performed a multicenter retrospective cohort study of adult heart transplant recipients in the UNOS database from September 2023 to June 2025. Donor-recipient mismatch was calculated for total PHM and separately for LV and RV predicted mass. The primary outcome was severe PGD within 24 h. RESULTS: Among 5,270 recipients, 387 (7.3%) developed severe PGD. Total PHM mismatch was not associated with PGD (global p = 0.39). In contrast, RV oversizing demonstrated a significant, nonlinear association with PGD (global p = 0.01), with increased risk emerging at approximately +15% RV oversizing. LV mismatch showed a weaker association, with elevated risk only at extreme undersizing. Separating PHM into ventricular-specific components significantly improved risk classification compared with total PHM (overall NRI 18.9%; 95% CI, 15.4%-21.4%). A ventricular asymmetry phenotype characterized by concurrent LV undersizing and RV oversizing, though uncommon, was associated with markedly higher PGD risk (adjusted OR 2.79; 95% CI, 1.46-5.33). No effect modification by pulmonary vascular resistance was observed. CONCLUSIONS: Ventricular-specific sizing, particularly RV mismatch, provides superior discrimination for severe PGD and highlights RV oversizing as an underrecognized contributor to early allograft failure. These findings support a shift toward biventricular, donor-recipient matching.