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The Journal of Heart and Lung Transplantation
International Society for Heart and Lung Transplantation.

Major advantages and critical challenge for the proposed United States heart allocation system

      The proposed new United States allocation system incorporates extensive research into an elegant plan designed to reduce wait list mortality while preserving post-transplant outcomes. All architects are to be congratulated. However, the future cannot be reliably modeled from the past as listing practices will evolve in response to new criteria. The new system should provide a major advance if and only if it is combined with a commitment to limit the number of listed patients overall and within each high priority status to the number that could reasonably undergo timely transplantation.

      Keywords

      Modeling the new system

      The proposed new allocation system represents a remarkably strong advance. It incorporates extensive research on the prevalence and outcomes of current candidates with highly detailed classification into a plan designed to reduce mortality while waiting, while preserving excellent outcomes post-transplant. The architects of this plan and the analysts who provided the data in this format merit the highest commendation. We would like to take this opportunity to discuss some specific challenges and possible opportunities for refinement of the proposed system.
      The modeling for the proposed new system also reflects considerable expertise and thought based on current listing practice. However, it cannot overcome the fundamental reality that future listing behavior cannot be modeled based on previous listing behavior if the rules are changing. Analogous to the Heisenberg uncertainty principle, the process of defining the conditions will alter them. Listing practices will quickly evolve in response to future priority criteria.
      This adaptive behavior became strikingly evident after the last major change in status IA criterion to require an indwelling pulmonary artery catheter with high-dose intravenous inotropic therapy. At that time, such therapy was said to be was too invasive to ever be used unless absolutely warranted by the acuity of hemodynamic compromise. Nonetheless, hospital units evolved to house patients waiting weeks to months with indwelling pulmonary artery catheters in order to get access to donor hearts, even despite numerous auditing challenges and some severe penalties. Clear evidence of this ongoing adaptation is found in the 18% of exceptions in the current status IA listing that are due to inadequate access for indwelling catheters. This is primarily the result of too many such catheters being inserted and maintained in central veins. Another example of adaptation to new rules is the increasing use of intra-aortic balloon pump (IABP) support through the subclavian artery to allow ambulation during long waiting times in hospital.

      Policing escalation for priority?

      Can we create tight clinical specifications to prevent escalation that is not medically urgent? The hemodynamic criterion of a cardiac index of 2.2 liters/min/m2 is much too loose, because many people with these cardiac indices are functioning comfortably at home, although with restricted outside activity. Lowering it to below 2.0 liters/min/m2 is more restrictive, but that can still be influenced by the decision regarding continuation or downtitration of a β-blocker, which is part of optimal recommended therapy. Reluctance to escalate diuretic therapy aggressively can also affect multiple risk parameters for advanced heart failure. Treating to the priority is almost as fundamental as studying to the test. The more the stakes are perceived as life-and-death, the more intense the pressure to measure up.
      Enforcing behavior that is contrary to incentives is unrealistic. Ideally, the transplant community should converge into harmony with uniform listing practices, but transplant physicians also feel deeply their obligation to serve as advocates for their individual patients. It should be recognized that treating to the priority may be perceived in some cases as in the best interest of the patient who needs a transplant to avoid death in the near future when there is otherwise a small chance of timely transplantation. Setting up tribunals to assess this practice is certainly possible, but what are the statutes, and who should judge?
      Consider the common situation of a patient at risk on home inotropic therapy with progressively worsening renal function and early evidence of right heart dysfunction. Even if the patient could get by with a left ventricular assist device (LVAD) alone, the mortality at 1 year for bridge to transplant on continuous-flow devices is approximately 12%, and approximately 30% of the survivors at 1 year have been removed from the active list for transplant, most due to complications.
      • Teuteberg J.J.
      • Stewart G.C.
      • Jessup M.
      • et al.
      Implant strategies change over time and impact outcomes: insights from the INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support).
      It would be hard to determine whether this risk is preferable to the risk of spending a couple of days or weeks on extracorporeal membrane oxygenation (ECMO) or a ventilator in hopes of getting a transplant without first going through another major cardiac surgery and then the wait for device complications. Without placing a value judgment on such evolving behavior, it should be recognized that most centers will give serious consideration to developing “ambulatory ECMO” programs as an alternative to urgent placement of a durable device if transplantation is the clear objective.

      Limiting the waiting list to align with donor heart supply

      We have already seen the inexorable trend toward escalation to the highest priority in the current system, which has been a major driver of efforts for revision. With any new system, including the currently proposed one, there would be an initial dispersion of priorities in the top 3 or 4 tiers, but upward escalation would soon become evident. Prepare to track the increasing use of ECMO, IABP, and non-dischargeable VADs. Anticipate ingenious ways to prevent deconditioning of patients on this support for extended periods of time.
      A fundamental condition for the success of the new allocation system is that patients who are considered to have sufficiently severe illness to warrant transplantation can expect to undergo transplantation within a reasonable period of time. This is certainly not true now, when many patients across the country are waiting more than 6 to 12 months in status IA, originally intended for patients with less than 7 days to live without transplant.
      Region 1 currently provides a model of the future for other regions: more than 90% of all hearts go to status IA patients. There is virtually no transplantation for status IB patients, except for blood type AB, and status II patients are essentially parked until they become sicker. Although region 1 presents the extreme evolution of this problem, other regions are converging on this crisis.
      • Stevenson L.W.
      Crisis awaiting heart transplantation: sinking the lifeboat.
      Several regions are supporting their highest priority candidates through evaluation in other regions where waiting times are more favorable. This travelling for transplant clearly discriminates against patients with fewer personal resources, and is thus an extreme violation of the ethical mandate of equal access to donor organs.
      In addition to the overall balance of patients who are listed and receive a transplant, the expected waiting time within a priority level would need to match the severity of illness, so the number of patients in each level would need to be smaller than in the level below in a steep pyramid. For instance, the likelihood of transplantation would need to be within a few days for patients on ECMO; for patients on an IABP, it should ideally be less than 1 month, and perhaps a few months on multiple inotropes or with a serious LVAD complication. Nothing about the new system will guarantee that it will be realistic in the future unless this tier of arithmetic is considered.
      The only way to prepare for the success of this system or any priority system is to limit the number of patients who are listed to more closely approximate the number of hearts likely to become available. This would need to be true for the overall number of listed patients, which in the United States currently exceeds the number of donors by almost 50% each year. Adding the patients already listed to the number likely to be listed this year equals almost 7,000 adult patients, for an anticipated supply of about 2,200 hearts.
      • Stevenson L.W.
      Crisis awaiting heart transplantation: sinking the lifeboat.
      Although we realize that limiting the pool of listed patients was not part of the charge to the United Network of Organ Sharing committee, we believe that strong consideration should be given to simultaneously addressing this critical component of the supply-and-demand equation. No priority system can correct this severe supply-and-demand imbalance. Over time the balance would also need to be maintained within each of the high priority statuses to make sure that not more people are entering the status than would reasonably expect to receive transplantation before an adverse event while waiting.
      The transplant community should commit to a coordinated effort to limit the number of patients listed annually to the number that can reasonably receive hearts in a year. This would need to be done as a nationwide effort to avoid local competition and program shopping for the less ideal patients undergoing evaluation. This collaboration would seek to characterize patients most likely to derive lasting benefit from transplantation. It would counterbalance the recent trend to advocate expanding transplant eligibility despite traditional comorbidities associated with the significant although small aggregate reduction in post-transplant survival. The complexity of this effort is high, but it is indeed an obligation of the transplant community committed to equitable access for a precious resource.
      The new allocation system promises to provide a major advance to the transplant community, if combined with a commitment to limit the number of listed patients overall and within each high priority status to the number that could reasonably undergo timely transplantation. With these complementary strategies, the maximal benefit from this truly miraculous therapy can be realized.

      Disclosure statement

      The authors have no conflicts relevant to this article.
      All authors are co-principal investigators of INTERMACS and R.L.K., J.B.Y., J.K.K., and S.A.H. are past presidents of the International Society of Heart and Lung Transplantation. These views represent the views of the authors but not that of the official position of the ISHLT or the JHLT.

      References

        • Teuteberg J.J.
        • Stewart G.C.
        • Jessup M.
        • et al.
        Implant strategies change over time and impact outcomes: insights from the INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support).
        JACC Heart Fail. 2013; 1: 369-378
        • Stevenson L.W.
        Crisis awaiting heart transplantation: sinking the lifeboat.
        JAMA Intern Med. 2015; 175: 1406-1409