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 went into effect October 18, 2018. The revised policy reflected the need to reassess prioritization of heart transplantation candidates and eliminate geographic disparities in access. It was designed to equitably allocate donor hearts to patients with the highest risk for mortality across geographic regions and increase the transplantation rate. The OPTN's former three-tier (Status 1A, 1B, and 2) stratification system was expanded to six tiers (Status 1-6) to better categorize candidates and includes statuses for certain high-risk conditions, such as congenital heart disease and dual organ transplantation. Here, we take a closer look at the impact that the 2018 OPTN policy has had on wait-list and posttransplantation outcomes, geographic sharing of donor organs, and use of temporary mechanical circulatory support.
Following the Final Rule
The National Organ Allocation Policy's Final Rule, which establishes the regulatory framework for organ allocation, mandates that OPTN policies promote equitable allocation. One of the goals of the final rule is to ensure the distribution of organs "over as broad a geographic area as feasible…, and in order of decreasing medical urgency." However, the prior OPTN policy was no longer in compliance with these tenets. One unforeseen contributor was the advent of left ventricular assist devices (LVADs). Under the old policy, stable candidates with LVADs were prioritized, however, as outcomes in patients with LVADs improved, such prioritization no longer seemed justified. Moreover, the rapid increase in candidates with LVADs resulted in longer wait times. In addition, despite prior policy revisions, geographic variation in access to transplantation and unacceptably high wait-list mortality among the sickest candidates persisted.
The most significant changes to the OPTN allocation policy were those prioritizing patients with short-term circulatory support devices. Under the previous system, Status 1A, the highest urgency status, comprised critically ill patients, such as those requiring extracorporeal membrane oxygenation (ECMO) and stable patients with LVADs. Both of these patient groups therefore had the same medical urgency and competed for donors equally despite disparate outcomes: Heart transplantation candidates on ECMO have among the highest mortality on the wait list. Lower projected posttransplantation survival has also been observed in ECMO candidates who had renal insufficiency or required mechanical ventilation. Stable patients with LVADs have outcomes similar to those of candidates without LVAD. To address this, the new allocation system reassigned the qualifying criteria for Status 1A to Statuses 1, 2, and 3, in descending order of urgency based on wait-list mortality. Most notably, 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 major concerns with the new policy were the potential for worse posttransplantation outcomes resulting from transplantation in higher-risk patients, lack of consideration of posttransplantation outcomes in the development of the new policy, and an unwarranted increase in the use of ECMO and other short-term devices. Although the true impact of the new policy on posttransplantation survival is not clear, it is clear that the preferred mode of bridging to transplantation has shifted drastically from LVAD to short-term devices. According to the OPTN/Scientific Registry of Transplant Recipients 2019 data report, between 2017 and 2019, candidates with an LVAD decreased from 47.8% to 33.5%, ECMO increased from 1.2% to 6.0%, and IABP more than tripled from 8.3% to 29.7%.
New Policy: What Are the Outcomes?
After the new policy took effect, heart transplantation rates increased substantially for patients in the highest urgency category. In 2018, candidates classified as Status 1A were transplanted at a rate of about 302 per 100 wait-list–years. In 2020, candidates listed as Status 1 underwent transplantation at a rate of 2086 per 100 wait-list–years, and candidates listed as Status 2 at a rate of 1264 per 100 wait-list–years. Since implementation of the new policy, wait-list mortality has declined overall but not significantly, and high-urgency candidates continue to have high wait-list mortality.
Although there has been an approximately 40% reduction in wait-list time, an early analysis of the new policy suggested decreased posttransplantation survival. An update to this analysis showed no difference in survival. Yet, a subsequent analysis demonstrated a statistically significant decrease in 1-year survival of 4.6% and increased rates of new-onset dialysis and stroke after transplantation. Although each of these studies has limitations, their findings are concerning and warrant vigilance. Transplantation candidates receiving ECMO are among those at the highest risk and could negatively affect posttransplantation 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 1-year posttransplantation mortality.
As mandated by the Final Rule, access to organs "shall not be based on the candidate's place of residence or place of listing…" Under the prior OPTN policy, when a heart became available, it was first offered to Status 1A and 1B candidates at transplant hospitals within that donor service area before being extended to geographic zones. Now, when a donor heart becomes available, it is first offered to eligible Status 1 and 2 candidates within a 500-mile radius. While broadening access to organs, this change increased the distance traveled to retrieve an organ and in turn ischemic time, which could potentially worsen posttransplantation mortality. The impact of broadened access, however, is not yet clear.
The new heart allocation system appears to have had an effect on the choice of bridge-to-transplantation devices. For example, one cohort study found that durable LVAD use as a bridge to transplantation decreased from 41.9% to 25.5%, mirrored by more than fivefold and threefold increases in ECMO and IABP, respectively. This shift has led to increased wait times for candidates with durable LVAD. As a result, rather than implanting LVADs as a bridge, many centers have been bridging candidates with short-term devices in anticipation for expedited transplant for high-acuity patients. While this approach may expedite transplantation, it is not sustainable.
Goals Achieved and Continuous Distribution
While the OPTN achieved several of its goals through its extensive policy revisions (eg, broader sharing, increased transplantation in the sickest patients, possibly decreased wait-list mortality), unresolved issues remain, including prioritization of sensitized candidates. However, addressing sensitization was not feasible with the 2018 policy change due to insubstantial data, and it's anticipated that this issue will be addressed in future policy updates.
Further, despite studies (such as those previously mentioned) seeking to clarify posttransplantation outcomes under the new policy, variations in cohorts and methodology limit interpretability and comparison. It is clear that there has been a nationwide change in practice in response to the policy change. This is particularly evident in how short-term devices have replaced LVADs as the preferred bridge to transplantation.
Regarding future updates, the OPTN's next major change to transplant allocation policy will be moving from its current classification-based system to a continuous distribution system. Continuous distribution, the OPTN's new model for organ allocation, will consider multiple attributes of a candidate simultaneously, rather than placing candidates in rank order based on one factor. Attributes will include medical urgency, expected posttransplantation outcome, candidate biology, patient access, and efficiency of organ placement. The OPTN anticipates that this continuous-distribution policy will be more equitable and eliminate current hard boundaries that prevent further prioritization of a candidate.
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Cite this: Alyssa Chang, Monica M. Colvin. Are Heart Transplantation Outcomes Worse After the New OPTN Policy? - Medscape - Oct 11, 2022.