In 2018, the United Network of Organ Sharing (UNOS) and the Organ Procurement and Transplantation Network (OPTN) implemented a new allocation system for donor hearts with extended geographical sharing. The new system places patients in new medical urgency status classifications – Adult Status 1 through 6 – with specific status qualification criteria at listing.
The primary goals of the new heart allocation system are to better stratify candidates to reduce waitlist mortality, improve access to donor hearts for critically ill candidates and reduce the burden of exception requests.
OPTN data shows that the new heart allocation system has resulted in broader sharing, increased use of temporary mechanical circulatory support devices, significantly decreased median days to transplant and increased transplant rates for medically urgent candidates.
There was no significant change in waitlist mortality overall, but the new statuses do more accurately stratify medically urgent candidates, with Adult Status 1, 2 and 3 each having lower waitlist mortality than the previous status classifications. In addition, one-year transplant survival was unchanged, with one-year patient survival in the pre-implementation era at 91.1 percentcompared to 91.59 percent in the post-implementation era.
“Under the new system, hearts are going to the highest statuses,” says Shelley Hall, MD, FACC, FHFSA, FAST, Chief of Transplant Cardiology, Mechanical Circulatory Support and Advanced Heart Failure, Baylor University Medical Center at Dallas (Baylor Dallas), part of Baylor Scott & White Health and president of the Texas Chapter of the American College of Cardiology. “Under the former system, patients with the Status 1A classification accounted for 68 percent of all heart transplants. Today, patients with the equivalent Status 1-3 are receiving more than 80 percent of heart transplants.
“This has caused many transplant programs to change their behavior,” Dr. Hall continues. “Rather than stabilize patients with a durable left ventricular assist device or LVAD, patients are being placed temporarily on veno-arterial ECMO or an intra-aortic balloon pump, which gives them a higher status. In these cases, the patients go right to transplant. This has created an organ deficit for patients in the lower statuses. Currently, it looks like patients are either going to be transplant candidates or durable LVAD candidates, not both.”
In addition, the new heart allocation system has caused transplant teams to travel more as a result of increases in national and regional shares. Costs have increased because transplant programs often have to pay two organ procurement organizations. Total ischemic time has slightly increased from the previous low total ischemic time of three hours. Also, the massive volume of exception requests is now reviewed by other regions’ boards rather than the region’s own board, which has led to more anonymity and less accountability for decisions made.
“More exceptions are being filed than ever before. It’s rampant,” Dr. Hall says. “One transplant center’s definition of sick is not always the same as other centers. This part of the process has failed miserably. We need to address the problems in the current system and make modifications as feasible while we’re developing the continuous distribution system for hearts.”
In 2018, the UNOS/OPTN board of directors approved a “continuous distribution” model as a framework for future policy development and allocation of all organ types. This new framework moves organ allocation from pure recipient factors, and, instead, creates a rank-ordered classification from a combination of specific donor-recipient matching elements.
Candidates will be ranked by a total score determined by multiple factors called “attributes” or “elements,” such as medical urgency, patient outcomes, candidate biology, patient access and efficiency of organ transport. Doing so will dissolve hard boundaries that exist in the current, category-based system and help ensure that no single factor determines a patient’s priority on the waiting list. Work is projected to start in early 2023 on heart continuous distribution, and most likely will take three years to develop.
“Development of this process for hearts will be more complicated than other organs, which is one of the reasons it is the last to be developed,” Dr. Hall says. “Unlike the lung allocation score or model for end-stage liver disease score, we don’t have a continuous scoring system for hearts to build upon. And all of the assistive devices are a unique wrinkle for heart. We will have to determine how to weight them against each other.
“Our current allocation also is collecting a ton of risk stratification data in the hope we can identify key risk factors that will help in developing the continuous distribution system. The goal is always to develop the fairest, most equitable way to transplant the sickest patients. With a finite resource of donors and an ever-increasing list of candidates, even the best allocation systems merely rearrange the line order but never shorten the line.”