Outcomes in the 2018 UNOS donor heart allocation system: A perspective on disparate analyses

The United Network for Organ Sharing (UNOS) implemented a revised donor heart allocation system on October 18, 2018 with principle aims to reduce waitlist mortality, enhance geographic organ sharing, and improve organ distribution equity. Five recently published analyses compared outcomes of heart transplant (HT) recipients transplanted under the revised versus previous system. All demonstrated increased pre-transplant temporary mechanical circulatory support use and graft ischemic times under the revised system. However, despite using data from the same UNOS Registry, three analyses demonstrated increased risk of post-transplant mortality under the revised system, while two others found no significant difference in mortality risk. These studies differed in their analytic cohorts, study periods, follow-up duration, and statistical methodologies. Additionally, some may have introduced survivor bias or violated non-informative censoring. Given these variable findings, longer-term outcome assessment is warranted before the HT community can truly understand the impact of the 2018 UNOS system revision on post-transplant outcomes.