Evaluation of the OPTN Six-Status Heart Allocation System and a Combined Prognostic Model for Waitlist Risk Evaluation

In December 2016, the Organ Procurement and Transplantation Network (OPTN) approved a bylaw that restructured the national heart allocation policy from a three-status to a six-status system. This new allocation system, which aimed to assign the highest priority to the patients with the highest mortality risk, went into effect on October 18, 2018. Since then, studies have identified limitations with the current system. However, no changes have been made to improve the national heart allocation system. Given the clear importance and impact of ranking patients based on medical urgency, we carefully evaluated the six-status heart allocation system to determine its correlation with observed mortality, or calibration, and its ability to predict six-month patient mortality risk and waitlist survival. The primary outcome of this study was the validation of the calibration and prognostic performance of the current heart allocation system. The secondary outcome is a simple model that greatly improves upon the current system's ability to accurately (>80%) predict waitlisted patient mortality. With a mean calibration slope of 0.94 (0.66, 1.21) and an area under the receiver operating curve of 0.71 (0.47, 0.87), the current allocation system is poorly calibrated, has only moderate statistical discrimination, and underestimates patient risk in the most critically ill patients. Hazard and time-series regression analysis confirmed that the six-status system does not adequately rank patients based on medical urgency. Our combined model demonstrates that the national allocation system can be improved. While the current heart distribution system accounts for some patient risk factors, a more objective and accurate model is needed to achieve the OPTN's strategic objective to more reliably model and predict patient risk and survival likelihood. Our model more accurately predicts patient waitlist mortality and will better inform waitlist management and improve waitlist survival by prioritizing medical urgency.