UNOS 2018 Heart Allocation Policy: Evaluation of Status 1 and 2 Extensions on Heart Transplant Outcomes

The new United Network of Organ Sharing (UNOS) allocation policy emphasizes those supported by mechanical circulatory support devices (MCSD). We evaluated the outcomes based on temporary mechanical circulatory support (TMCS) devices that have a timeline restriction (Status 1: Veno-Arterial Extra-Corporeal Membrane Oxygenation (VA-ECMO) and Status 2: Intra-Aortic Balloon Pump (IABP) and Impella) and extension status among Status 1 and 2 patients.

The UNOS database was used to identify adult patients (age > 17) listed for heart transplants as Status 1 or 2 at any point during their listing from October 2018 to June 2024.

Among Status 1 patients, extensions have stayed steady throughout the years but with significant regional variations across the UNOS region (0%-30.2%). Those extensions granted had worse waitlist outcomes but comparable post-transplant survival. Among Status 2 patients, the use of IABP and Impella has significantly increased over the years, with the use of extensions increased during our study period. The majority of the patients were supported on IABP. Again, regional variations existed with the UNOS region that ranged from 12% to 25% use of the extension. Those who were extended had better waitlist survival, with comparable post-transplant outcomes (p < 0.05).

The timeline restriction for Status 1 and 2 patients with TMCS are not seen in practice with more patients remaining in their respective status through extensions. Extension criteria as well as timeline restriction should be revisited in the UNOS heart allocation policy.