Use of mechanical circulatory support and survival for heart and heart-kidney transplant recipients in the new allocation system

Background: The 2018 United Network for Organ Sharing organ allocation change aimed to distribute donor hearts to the sickest patients on the waitlist. Whether this change differentially affected outcomes in heart-only vs heart-kidney transplant recipients is unknown. Methods: This study used the Scientific Registry of Transplant Recipients to compare outcomes, including survival, of heart-only and heart-kidney transplant recipients from 2015 to 2021, from the old vs new allocation system, including use of mechanical circulatory support (MCS), prior to transplant. Results: During the study period, 16,696 patients underwent heart transplant alone (9,320 in the old and 7,376 in the new system) and 1,156 patients underwent heart-kidney transplant (529 in the old and 627 in the new system). For both heart and heart-kidney transplant populations, there was a 3- to 5-fold increase in the use of temporary MCS. Heart-only recipients had worse survival when temporary MCS was used in the old allocation system. Heart-only recipients with durable MCS had worse survival both in the old and the new allocation system. There was no difference in survival in heart-kidney recipients in the old vs new allocation system, regardless of MCS use. Conclusions: The new heart allocation system was associated with increased use of temporary MCS in both heart and heart-kidney recipients. However, this change only differentially affected survival in heart-only recipients with improved survival if on temporary MCS, but worse survival if on durable MCS. Unlike prior studies, heart-kidney recipients did not have different outcomes after the heart allocation change, which may reflect outcomes in more current times.