In 2016, the Organ Procurement and Transplantation Network (OPTN), which is administered by the United Network for Organ Sharing (UNOS), approved a new heart allocation policy that came into effect on October 18. 2018. The revised policy reflected the need to reassess prioritization of heart transplant candidates and eliminate geographic disparities in access. It was designed to fairly allocate donor hearts to patients with the highest mortality risk across all geographic regions and increase the transplant rate. The previous OPTN three-tier (Status 1A, 1B and 2) stratification system has been expanded to six tiers (Status 1-6) to better categorize applicants and includes statuses for certain high-risk conditions, such as as congenital heart disease and bi-organic diseases. transplantation. Here, we take a closer look at the impact that the OPTN 2018 policy has had on post-transplant waiting lists and outcomes, the geographic sharing of donor organs, and the use of temporary mechanical circulatory support.
Follow the final rule
The final rule of the National Organ Allocation Policy, which establishes the regulatory framework for organ allocation, states that OPTN policies promote equitable allocation. One of the purposes of the final rule is to ensure the distribution of organs “over as wide a geographic area as possible…and in descending order of medical urgency.” However, OPTN’s previous policy was no longer consistent with these principles. An unforeseen contributor has been the advent of left ventricular assist devices (LVADs). Under the old policy, stable candidates with LVAD were prioritized, however, as outcomes in patients with LVAD improved, such prioritization no longer seemed warranted. In addition, the rapid increase in the number of candidates with LVADs has resulted in longer waiting times. Moreover, despite previous policy revisions, geographic variations in access to transplantation and unacceptably high mortality on waiting lists among the sickest candidates have persisted.
The most significant changes to OPTN allocation policy were those that prioritized patients with short-term circulatory assist devices. In the previous system, status 1A, the highest emergency status, included critically ill patients, such as those requiring extracorporeal membrane oxygenation (ECMO), and stable patients with LVADs. These two groups of patients therefore had the same medical emergency and competed for donors equally despite disparate results: candidates for heart transplantation under ECMO have the highest mortality on the waiting list. Lower projected post-transplant survival was also observed in ECMO candidates who had renal impairment or required mechanical ventilation. Stable patients with LVAD have similar results to candidates without LVAD. To address this issue, the new allocation system reassigned the qualification criteria for Status 1A to Statuses 1, 2, and 3, in descending order of urgency based on waitlist mortality. Specifically, under the new system, candidates on ECMO are now classified as status 1, and those with an intra-aortic balloon pump (IABP) as status 2.
Some of the main concerns with the new policy were the potential for worse post-transplant outcomes resulting from transplantation in high-risk patients, the lack of consideration of post-transplant outcomes in the development of the new policy, and an unwarranted increase in use of ECMO and other short-term devices. Although the true impact of the new policy on post-transplant survival is unclear, it is clear that the preferred mode of transition to transplantation has changed dramatically, from LVADs to short-term devices. According to the 2019 OPTN/Scientific Registry of Transplant Recipients data report, between 2017 and 2019, candidates with LVAD decreased from 47.8% to 33.5%, ECMO decreased from 1.2% to 6 .0% and the IABP more than tripled from 8.3% to 29.7%.
New policy: what are the results?
After the new policy took effect, heart transplant rates increased significantly for patients in the highest urgency category. In 2018, applicants classified as 1A were transplanted at a rate of approximately 302 per 100 waiting list years. In 2020, candidates listed in status 1 underwent transplantation at a rate of 2086 per 100 waiting list years, and candidates listed in status 2 at a rate of 1264 per 100 waiting list years. Since the implementation of the new policy, waitlist mortality has declined overall, but not significantly, and high urgency applicants continue to have high waitlist mortality.
Although there was a reduction of about 40% in waiting time, an initial analysis of the new policy suggested a decrease in survival after transplantation. An update of this analysis showed no difference in survival. Yet, subsequent analysis demonstrated a statistically significant decrease in 1-year survival of 4.6% and increased rates of dialysis and recent-onset stroke after transplantation. Although each of these studies has limitations, their findings are concerning and warrant vigilance. Transplant candidates receiving ECMO are among the most at risk and could negatively affect post-transplant outcomes. In addition to the increase in candidates with ECMO, there is now a higher proportion of candidates with congenital heart disease, a group with historically high post-transplant mortality at 1 year.
As required by the final rule, access to organs “shall not be based on the candidate’s place of residence or place of registration…” Under previous OPTN policy, when a heart became available, it was first offered to applicants for status 1A and 1B at transplant hospitals in that donor service area before being expanded to geographic areas. Now, when a donor heart becomes available, it is first offered to eligible status 1 and 2 applicants within a 500 mile radius. While expanding access to organs, this change increased the distance traveled to retrieve an organ and, therefore, ischemic time, which could potentially worsen post-transplant mortality. The impact of expanded access, however, is not yet clear.
The new cardiac allocation system appears to have had an effect on the choice of transition devices to transplantation. For example, a cohort study found that sustained use of LVAD as a gateway to transplantation increased from 41.9% to 25.5%, reflected in more than five- and three-fold increases in ECMO and ‘IABP, respectively. This change has resulted in increased wait times for applicants with a durable LVAD. As a result, rather than implanting LVADs as a bridge, many centers have bridged candidates with short-term devices in anticipation of expedited transplantation for high-acuity patients. Although this approach may expedite transplantation, it is not sustainable.
Goals achieved and continued distribution
Although the OPTN has achieved many of its goals through its broad policy revisions (e.g., wider sharing, increased transplantation in the sickest patients, possibly decreased wait-list mortality ), unresolved issues remain, including the prioritization of sensitized candidates. However, it was not possible to address outreach with the 2018 policy change due to insubstantial data, and it is expected that this issue will be addressed in future policy updates.
Moreover, despite studies (such as those mentioned previously) seeking to clarify post-transplant outcomes under the new policy, variations in cohorts and methodology limit interpretability and comparison. It is clear that there has been a change in practice nationwide in response to the change in policy. This is particularly evident in how short-term devices have replaced LVADs as the preferred gateway to transplantation.
As for future updates, OPTN’s next major change to the transplant allocation policy will be to move from its current classification-based system to a rolling distribution system. Continuous Distribution, OPTN’s new organ allocation model, will consider multiple attributes of a candidate simultaneously, rather than ranking candidates in rank order based on a single factor. Attributes will include medical urgency, expected post-transplant outcome, candidate biology, patient access, and organ placement efficiency. OPTN anticipates that this continuous distribution policy will be more equitable and eliminate the current rigid boundaries that prevent further prioritization of a candidate.
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