Donor Right Ventricular Oversizing Is Independently Associated With Severe Primary Graft Dysfunction After Heart Transplantation: A Multicenter Retrospective Analysis.
Ahmad A, Wang C, et al. • Clinical transplantation • 2026
Ventricular-specific sizing, particularly RV mismatch, provides superior discrimination for severe PGD and highlights RV oversizing as an underrecognized contributor to early allograft failure, supporting a shift toward biventricular donor-recipient matching.
Key Findings
Results
Total predicted heart mass (PHM) mismatch was not associated with severe primary graft dysfunction (PGD) after heart transplantation.
Among 5,270 adult heart transplant recipients, 387 (7.3%) developed severe PGD within 24 hours.
The global p-value for total PHM mismatch and PGD was 0.39, indicating no statistically significant association.
Data were drawn from the UNOS database covering September 2023 to June 2025.
This finding suggests that total PHM, the widely used current standard for donor-recipient size matching, does not predict early graft failure.
Results
Right ventricular (RV) oversizing demonstrated a significant, nonlinear association with severe PGD, with increased risk emerging at approximately +15% RV oversizing.
The global p-value for RV oversizing and PGD was 0.01.
The association was nonlinear, with risk increasing at the threshold of approximately +15% RV oversizing.
This association was independent of other covariates as determined by multivariable analysis.
RV oversizing was identified as an 'underrecognized contributor to early allograft failure.'
Results
Left ventricular (LV) mismatch showed a weaker association with severe PGD, with elevated risk only at extreme undersizing.
Unlike RV oversizing, LV mismatch did not show a broad association with PGD across the range of mismatch values.
Elevated PGD risk from LV mismatch was observed only at the extreme end of undersizing.
This contrasts with the more prominent and clinically relevant nonlinear effect observed for RV mismatch.
Results
Separating PHM into ventricular-specific components significantly improved risk classification for severe PGD compared with total PHM.
The overall Net Reclassification Improvement (NRI) when using ventricular-specific sizing over total PHM was 18.9%.
The 95% confidence interval for the NRI was 15.4% to 21.4%.
This improvement in risk classification supports the clinical utility of biventricular assessment over aggregate heart mass metrics.
Results
A ventricular asymmetry phenotype characterized by concurrent LV undersizing and RV oversizing was associated with markedly higher PGD risk.
The adjusted odds ratio for severe PGD in recipients with concurrent LV undersizing and RV oversizing was 2.79.
The 95% confidence interval was 1.46 to 5.33.
This phenotype was described as 'uncommon' in the study population.
This phenotype represents the combination of two independently unfavorable ventricular mismatch directions occurring simultaneously.
Results
No effect modification by pulmonary vascular resistance (PVR) was observed on the relationship between RV oversizing and severe PGD.
The analysis specifically tested whether PVR modified the association between RV oversizing and PGD.
The absence of effect modification suggests that RV oversizing contributes to PGD through mechanisms that are not dependent on recipient pulmonary vascular resistance.
This finding has implications for understanding the physiologic mechanism by which RV oversizing leads to early graft dysfunction.
Methods
The study was a multicenter retrospective cohort analysis using the UNOS database in the modern allocation era.
The study included 5,270 adult heart transplant recipients.
Data were collected from September 2023 to June 2025, representing the modern UNOS allocation era.
Donor-recipient mismatch was calculated separately for total PHM, LV predicted mass, and RV predicted mass.
The primary outcome was severe PGD within 24 hours of transplantation.
What This Means
This research suggests that the way doctors currently match heart donors to recipients by size may be missing important information. The standard approach uses a measure called 'predicted heart mass' (PHM) to estimate overall heart size compatibility between donor and recipient. However, this study of over 5,000 heart transplant patients found that total heart mass matching was not actually linked to a serious early complication called primary graft dysfunction (PGD), where the transplanted heart fails to work properly within the first 24 hours. Instead, when researchers looked at the left and right chambers of the heart separately, they found that having a donor right ventricle (the chamber that pumps blood to the lungs) that is too large relative to the recipient's — specifically more than about 15% larger — was significantly associated with increased PGD risk.
The study also found that when a donor heart had both an undersized left ventricle and an oversized right ventricle at the same time (a pattern called 'ventricular asymmetry'), the risk of severe PGD was nearly three times higher than in patients without this pattern. Measuring the two chambers separately was substantially better at identifying which patients were at risk for this complication compared to just using the combined heart mass measurement, improving risk classification by about 19%. Importantly, these effects were not explained by the recipient's pulmonary vascular resistance, a measure of how hard the right side of the heart has to work.
This research suggests that current heart transplant size-matching practices, which rely on a single combined heart mass estimate, may be leaving important risk factors undetected. Moving toward a 'biventricular' matching approach — where the left and right ventricles are assessed separately — could help identify higher-risk donor-recipient pairings before transplantation and potentially guide clinical decisions to improve early outcomes after heart transplantation.
Ahmad A, Wang C, Petrovic M, Williams A, Trahanas J, Bommareddi S, et al.. (2026). Donor Right Ventricular Oversizing Is Independently Associated With Severe Primary Graft Dysfunction After Heart Transplantation: A Multicenter Retrospective Analysis.. Clinical transplantation. https://doi.org/10.1111/ctr.70675