Are exceptions justified in the current heart allocation system?

In the current six-tiered heart allocation system, waitlisted candidates frequently receive an exception to any of the top four allocation statuses. Studies have shown varying results regarding the mortality risk of exceptions compared to standard criteria listings in the top two statuses. It remains unclear whether exception statuses in the current allocation system are justified. We performed a retrospective cohort study on all adults waitlisted for heart transplant between November 1st 2018 and December 31st 2022, contained in the United Network for Organ Sharing database. The waitlist mortality and transplantation rate of all exception status and standard criteria listings were compared and ranked, using status 6 as the reference status, in univariable and multivariable Cox models including status as a time-dependent variable. A total of 17116 heart waitlist candidates were included in the study. The waitlist mortality rates of exceptions in status 1 and 2 were lower than, but close to, the mortality rates of their standard criteria counterparts: status 1 standard HR 43.47 (p<0.001), status 1 exception HR 31.48 (p<0.001), status 2 standard HR 10.21 (p<0.001), status 2 exception HR 7.76 (p<0.001). The mortality rate of exceptions in status 3 and 4 was higher than, but also close to, the mortality rate of their standard criteria counterparts: status 3 standard HR 2.61 (p<0.001), status 3 exception HR 4.18 (p<0.001), status 4 standard HR 1.31 (p=0.104) and status 4 exception HR 2.13 (p<0.001). Based on waitlist mortality over a longer study period than previous analyses, high-priority exceptions are appropriately placed in the current heart allocation system. The current allocation system requires a large fraction of candidates to seek exceptions, suggesting that we should focus on objective data to risk stratify all heart waitlist candidates, and thereby reduce the need for exceptions.