Development and Validation of an Adult Medical Urgency Score for US Donor Heart Allocation

Importance One in 5 heart transplant candidates in the US die or are delisted without transplant. Donor hearts are currently allocated by a 6-status therapy-based system criticized for limited risk stratification and susceptibility to gaming. Objective To develop a new heart allocation policy based on an objective medical urgency score that ranks candidates based on the interaction between physiology and mechanical circulatory support. Design, Setting, and Participants Registry-based observational study using data from the US organ transplant system. All adult (aged ≥18 years) heart transplant candidates from January 2019 to August 2025 were included, split into training (2019-2023), validation (2023-2024), and test (2024-2025) datasets. Main Outcomes and Measures A marginal structural model of 6-week mortality without transplant was estimated (the US Candidate Risk Score [US-CRS]). Eight models were compared in held-out data by weighted time-dependent area under the curve (AUC) and calibration by status. Finally, US-CRS was converted into an allocation policy and a match-run simulation of waitlist reordering was performed compared with the current 6-status system. Results Adult heart transplant candidates were partitioned into consecutive training (n = 21 859), validation (n = 7897), and test (n = 8256) datasets (mean [SD] age, 53 [13] years; 74% male). The chosen US-CRS model included 5 laboratory values and 4 therapeutic devices (durable left ventricular assist device, intra-aortic balloon pump, microaxial flow pump, and advanced mechanical circulatory support). In test-set cross-sections of candidates actively waiting on the same calendar date, US-CRS had similar or significantly higher time-dependent AUC than the current 6-status system (mean AUC, 0.807 vs 0.693, respectively) and acceptable calibration by status, especially for candidates who received their status by exception. In match-run analysis (n = 45 530 donor hearts), a US-CRS–based system led to 67% of transplant recipients moving down in rank order and increased observed 6-week transplant-censored mortality for the first candidate on the match run from 11.2% (95% CI, 10.1%-12.5%) under the current system to 15.7% (95% CI, 13.9%-17.6%) under the US-CRS–based system. Conclusions and Relevance In this registry-based study of US heart transplant candidates, a US-CRS–based allocation system prioritized sicker candidates with higher mortality without transplant compared with the current medical urgency statuses.