Cardiac size and sex-matching in heart transplantation : size matters in matters of sex and the heart.

OBJECTIVE: This study evaluated whether worsened outcomes in sex mismatch are related to mismatch of organ size in heart transplantation.
BACKGROUND: Sizing for organ allocation in heart transplantation currently incorporates only body weight differences between the donor and recipient. Weight correlates poorly to cardiac size, and donor–recipient weight differences are not associated with differential survival. Heart size correlates with sex, and donor–recipient sex mismatch conveys worse-than-expected outcomes.
METHODS: We performed a retrospective cohort study of 31,634 donor–recipient adult heart transplant pairings from the United Network for Organ Sharing transplantation registry. We used predictive models to calculate the predicted total heart mass (pHM) for recipient and donor pairs. We assessed organ size mismatch by calculating the percent difference between the donor and recipient pHM as [(pHM(recipient) – pHM(donor))/(pHM(recipient))]*100.
RESULTS: The most-undersized pHM septile demonstrated higher mortality during the first year post-transplantation (hazard ratio [HR]: 1.27; p < 0.001), which remained robust in adjusted models (HR: 1.25; p = 0.03). Survival did not vary across septiles of weight differences. On univariate analysis, sex mismatch was associated with higher mortality in male patients, but not in female patients. Controlling for differences in pHM reversed these associations. Adjusted models demonstrated worse survival associated with sex mismatch in female patients (1-year HR: 1.28; p = 0.02) but no difference in male patients (1-year HR, 1.00; p = 1.0).
CONCLUSIONS: Differences in donor–recipient pHM modulated the survival associated with donor–recipient sex mismatch and identified donor heart undersizing as an otherwise occult and potentially preventable cause of mortality following orthotopic heart transplantation.