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Commentaries

The Conundrum of Equitable Organ Allocation in Heart Transplantation

The Moving Target of Candidate Risk Score

Potena, Luciano MD, PhD1; Khush, Kiran K. MD, MAS2

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doi: 10.1097/TP.0000000000001841
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In Brief

Heart transplantation remains the therapeutic strategy that provides the greatest survival benefit for patients with advanced heart failure.1 However, the large and growing discrepancy between the need for transplantation and the critical shortage of suitable donor organs underscores the importance of developing appropriate and updated allocation strategies that continue to preserve justice and equity of access to this life-saving therapy.

Periodic revisions to organ allocation systems are necessary to reflect changing patient populations and treatment strategies. Of note, the challenges in this setting are related not only to the difficulty in standardizing the prognostic evaluation of patients, but also to the need for adjusting for the unfavorable allocation imbalance in blood group 0 candidates, and for the potential biases related to the behavior of physicians altering the intentions of allocation schemes.2 In the United States, for example, donor lungs were initially allocated to candidates based on time spent on the waitlist, blood type, and proximity of the donor to the candidate. Because mortality rates vary for different lung diseases, this system discriminated against candidates who were most likely to die while awaiting transplantation, such as those with idiopathic pulmonary fibrosis. This consideration, along with increasingly long waiting times, led to the implementation of the Lung Allocation Score (LAS) in 2005—a calculation of illness severity along with anticipated posttransplant survival that is designed to place the sickest candidates with the best chance of survival on the top of the waitlist. Adoption of the LAS decreased the size of the waitlist by reducing the incentive for early listing, and improved access to lungs for candidates at greatest risk of dying. Importantly, this was the first time “utility” of the transplant was included as part of an organ allocation policy.3

Similarly, the heart allocation policy is currently being revised in the United States to address the high waitlist mortality in the highest acuity (status 1A) patients. By increasing the granularity in classifications of heart failure severity, the new system aims to better reflect current use of mechanical assist devices and to address the disadvantages experienced by specific categories of patients, such as those with restrictive cardiomyopathies.4 The revised policy proposes a 6-tier system that gives highest priority status (tier 1) to candidates on mechanical ventilation, extracorporeal membrane oxygenation, and nondischargeable mechanical circulatory support (MCS). Subsequent tiers 2 and 3 classify patients by medical urgency, mainly by use of MCS, including use of ventricular assist devices, intra-aortic balloon pumps, and total artificial hearts. Although simulation models have predicted reduced waitlist mortality with the new allocation scheme, concern exists for increased use of these expensive and invasive therapies to prioritize patients and for a potential increase in posttransplant mortality.5 A heart allocation score analogous to the LAS was initially considered, but was abandoned due to the belief that it would take too long to develop and implement, would be too inflexible to modify during a time of rapidly changing MCS technology, and would lead to inaccurate estimation of mortality due to lack of adequate data collection.4 Thus, estimates of posttransplant mortality are not incorporated into the revised US heart allocation policy.

In Europe, on the other hand, the Eurotransplant consortium attempted to develop a cardiac allocation system that balances waitlist mortality with expected posttransplant survival, per validated risk scores. Although promising, simulations of this score showed that it was not applicable to patients with ventricular assist devices, thus limiting its utility to less than 50% of current candidates.6

In this issue of Transplantation, Jasseron et al7 analyzed the CRISTAL French National Transplant Database to develop a candidate risk score that prioritizes patients according to their medical urgency and risk of death while awaiting transplantation. In a retrospective cohort study that included all adult patients listed for a first heart transplant in France between 2010 and 2014, the authors derived and then validated a risk score that predicted 1-year waitlist mortality, and included a substantial number of patients on MCS. As opposed to classifying disease severity based on medical practice or medical assessment (such as need for hospitalization or inotropic support), which can be subjective, the authors focused on objective measures, such as comorbidities (diabetes mellitus) and laboratory test results (measures of liver and kidney function). This approach may be helpful to avoid “gaming” to prioritize individual patients and to provide objective evaluation of the short-term risk of death in candidates awaiting transplantation. The goal of this approach is to advocate the principle of distributive justice by providing more resources to those at greater immediate need.

The applicability of the score to patients with MCS, and the use of objective disease-driven parameters to derive it, clearly represents a step forward in the definition of a reliable allocation policy. The major weaknesses of the study are that the authors only used the candidate characteristics present at the time of initial listing, although candidates may wait months to years for transplantation, and the score may no longer accurately represent a candidate’s clinical status at the time of an organ offer. Another limitation is that expected posttransplant mortality has not been considered. Despite the authors’ statement that “access to transplantation will be denied to candidates with an expected 1-year posttransplant survival of 50% of lower,” it is unclear how expected survival will be calculated, and it can be argued that even thresholds below the 50% mark may represent unacceptable 1-year mortality risk, jeopardizing the equity of the system by allocating valuable organs to patients who are too ill to derive benefit from the procedure.

Effective prioritization of patients at high risk of dying is an ethical pillar that aims to guarantee justice in the management of the transplant waitlist. Organ allocation to patients at risk of excessive posttransplant mortality, on the other hand, does not preserve equitable access to care for less sick patients on the list, who may gain greater benefit from transplantation. Despite improvements, further efforts are needed to hit the moving target of the transplant candidate risk score, thereby achieving effective utilization of valuable and increasingly scarce donor organs for heart and other solid organ transplant procedures.8

REFERENCES

1. Lund LH, Edwards LB, Dipchand AI, et al. The Registry of the International Society for Heart and Lung Transplantation: Thirty-third Adult Heart Transplantation Report-2016; focus Theme: primary diagnostic indications for transplant. J Heart Lung Transplant. 2016;35:1158–1169.
2. Schnier KE, Turgeon NA, Kaplan B. A primer of neoclassical (traditional) and behavioral economic principles for organ transplantation: part 1. Transplantation. 2015;99:2024–2028.
3. Colvin-Adams M, Valapour M, Hertz M, et al. Lung and heart allocation in the United States. Am J Transplant. 2012;12:3213–3234.
4. Meyer DM, Rogers JG, Edwards LB, et al. The future direction of the adult heart allocation system in the United States. Am J Transplant. 2015;15:44–54.
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6. Smits JM, de Vries E, De Pauw M, et al. Is it time for a cardiac allocation score? First results from the Eurotransplant pilot study on a survival benefit-based heart allocation. J Heart Lung Transplant. 2013;32:873–880.
7. Jasseron C, Legeai C, Jacquelinet C, et al. Prediction of waitlist mortality in adult heart transplant candidates: the candidate risk score. Transplantation. 2017;101:2175–2182.
8. Schnitzbauer AA, Bechstein WO. Equitable distribution in rare indications for liver transplantation: the dilemma of the too small tablecloth continues! Transpl Int. 2017;30:451–453.
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