UNOS policy change is associated with attenuated risk of treated rejection in intra-aortic balloon pump-supported patients and no change with other MCS devices.

Objective. Whether the increased use of temporary mechanical circulatory support (tMCS) as a bridge to heart transplantation following the 2018 United Network for Organ Sharing (UNOS) policy change has translated to a different risk of treated rejection episodes is unknown.Approach. We analyzed adult heart transplant recipients listed and transplanted between November 1, 2010 and October 31, 2020 from the UNOS registry. Multinomial logistic regression was used to estimate relative risk ratios (RRRs) for post-transplant treated rejection, using patients who were alive without treated rejection as the reference category, and comparing tMCS device groups with the non-MCS cohort.Main results. A total of 22 634 patients were stratified by tMCS type [intra-aortic balloon pump, percutaneous device, extracorporeal membrane oxygenation, and surgically implanted dischargeable or non-dischargeable ventricular assist devices]. The RRR for treated rejection (vs alive and without treated rejection) was higher in the intra-aortic balloon pump (IABP) cohort compared to the non-MCS cohort in the pre era [RRR: 1.47 (1.25, 1.72);p< 0.001]. However, there was no difference for IABP versus non-MCS patients in the post era [RRR: 1.05 (0.85, 1.28);p= 0.66]. For other bridge-to-transplant therapies compared to the non-MCS cohort, RRRs were not significantly different based on policy era or tMCS sub-type.Significance. The 2018 UNOS policy change was associated with an attenuated relative risk of treated rejection amongst IABP-bridged recipients compared to the non-MCS cohort. These findings suggest that changes in allocation policy and associated shifts in waitlist dynamics may influence post-transplant immunologic risk profiles.