Abstract
BACKGROUND: In the US, donor hearts for transplant are currently allocated to the candidates with the highest risk of death on the waiting list, based on a categorical status-based system. The upcoming continuous distribution system provides an opportunity to implement a post-transplant risk score that may help avoid futile transplants. METHODS: In this observational study of the Scientific Registry of Transplant Recipients (SRTR), a novel US transplant risk score (US-TRS) was developed and validated using a mixed-effects Cox proportional hazards model. Study participants included adult heart transplant recipients between October 18, 2018, and February 28, 2022, split temporally into training (first 70% of recipients) and test (last 30% of recipients) datasets. We included 8 of 9 French Transplant Risk Score (French-TRS) components plus additional US variables that improved the Akaike Information Criterion (AIC) in the training data. In the test dataset, we assessed US-TRS 1-year post-transplant survival predictions with Uno's concordance index (c-index) and restricted mean survival time (RMST) and compared these results to other post-transplant risk scores, including the French-TRS, the Index for Mortality Prediction After Cardiac Transplantation (IMPACT) score, and recipients' waitlist status at transplantation. RESULTS: The study cohort consisted of 9,071 heart transplant recipients (mean age 54 [SD 13] years, 72% male), of which 828 (9.1%) died and 29 (0.3%) underwent retransplant within 1 year of transplant. The final US-TRS model included recipient age, bilirubin, estimated glomerular filtration rate (eGFR), albumin, durable left ventricular assist device (LVAD), diabetes, mechanical ventilation, congenital heart disease, donor age, donor sex, and donor-recipient size mismatch. The c-index in the test dataset was 0.671 (95% CI, 0.665-0.687) for the US-TRS model, 0.620 (95% CI, 0.611-0.632) for the French-TRS model, 0.598 for the calculated IMPACT score, and 0.551 (95% CI, 0.540-0.576) for waitlist Status at transplant. US-TRS estimated excellent survival for most recipients, but a minority (17%) of recipients were high risk with an estimated 1-year survival probability of 78% and an average estimated RMST of 311.9 days in the first year. CONCLUSIONS: In this registry-based study of US adult heart transplant recipients, a multivariable risk score outperformed existing models in predicting 1-year post-transplant survival and may be useful for integrating post-transplant survival into the upcoming continuous distribution framework.