5. Unmet challenges and future concerns

and implantable devices. In 2006, 8.9% of candidates were registered with MCS criteria. By 2015, MCS patients increased to 24.4% [8]. MCS has concurrently expanded to distinct applications, with a wide range of expected mortality. Patients with RVAD support experience a log10 higher mortality on the wait list compared to those with LVAD. The increased use of MCS has also resulted in a similarly complex array of complications. Clearly, the MCS per se is

A criticism of the 2006 policy between patient prioritization and geographic proximity was that the allocation rule was inconsistent with the UNOS mandate that access to organs "shall not be based on the candidate's place of residence or place of listing …" [12]. By first offering hearts to waiting list candidates listed as Status 1A and 1B at transplant hospitals within the DSA and then broadened to waiting list candidates in status listed 1A or 1B in surrounding Zones (A and B), geographically close, high acuity patients may have very different access and outcomes. A patient with high acuity patient at a hospital designated as Zone A, although only 25 miles away from the donor institution, could be listed to receive an offer after less acute

The 2006 paradigm for heart allocation places significant emphasis on patients with MCS, and prioritizing them for eventual transplant. As a consequence of this, the system has an inbuilt bias in favor of patients with systolic dysfunction. A large component of patients, such as those with lethal arrhythmia or heart failure with preserved ejection fraction (HFpEF), does not fit within this clinical spectrum [13]. Patients requiring exceptions to the group requiring exceptions is a heterogeneous group. The most common exceptions for status 1A were: (1) candidate is experiencing ventricular tachycardia or ventricular fibrillation; (2) candidate does not have intravenous access for inotropes or cannot tolerate a pulmonary artery catheter; and (3) congenital heart, while the most common exceptions for listing as status 1B were: (1) candidate is experiencing ventricular tachycardia or ventricular fibrillation; (2) congenital heart disease diagnosis; and (3) candidate requires a re-transplant. These six criteria comprise over half of those listed for exception. These patients are inherently susceptible to regional variability as their institution must first elect to apply for exception, which must be approved by the regional. Therefore, they were considered to ensure they not become marginalized in a new system. To be listed for OHT, these patients necessitate applying administrative exception for listing represents a growing component of

In 2016 the UNOS Thoracic Organ Transplantation Committee proposed changes to this allocation system, which were subsequently ratified. One of the first strategies proposed was the design of a heart allocation scoring system [8]. This is an attractive method in that a scoring system could provide a more objective method based on patient related data. This method is not without precedence. The Lung Allocation Score (LAS), which weighs pre-transplant morality risk against post-transplant survival, has been used in the allocation of donor lung grafts [14]. While the concept of a Heart Allocation Score (HAS) was strongly advocated by many, The

no longer suitable as a dichotomous gage for acuity and transplant listing.

patients within the DSA [8].

38 Heart Transplantation

the transplant candidate cohort.

4. The 2018 system

In spite of some substantial intrinsic changes to the heart donor allocation system, some important issues remain unaddressed. Some scenarios of concern were not addressed in the formulation of 2018 prioritization. Among this population of concern include highly sensitized recipients, those with adult congenital heart disease (ACHD), patients requiring multiple organ transplants. Similarly, potential issues regarding geographic redistribution remain.

Highly sensitized patients present a theoretically vulnerable cohort. Because of their high frequency of cross reactivity, they would presumably benefit require a broader donor pool. The 2006 allocation system provided some provisions for out of sequence prioritization of patients with high PRA. Few centers have reported complete PRA data; therefore, little data can be extrapolated to demonstrate the impact of sensitization on survival. Despite multiple attempts to provide appropriate priority for highly sensitized patients, sufficient data did not exist within the SRTR to develop appropriate offsets.

ACHD represents several challenges for allocation. The 2006 system necessitated application for an exception for optimal prioritization, which may be subject to inconsistent regional preferences and biases. The natural history of ACHD is a full spectrum of complex cardiac. There is still room to develop consistent criteria that are comparable to other cardiac diseases.


transplant centers encompassed by these widening circles be factored into this algorithm? Further, all Organ Procurement Organizations do not perform equally, with regional, cultural, and religious differences contributing to willingness to donate as well as inherent differences in OPO practices and efficiencies. Should geography be indexed to create equal access in potential organ offers? Lastly organ acceptance varies greatly from program to program [16]. By offering wider circles of potential organ offers, is the new system incentivizing conservative acceptance practices instead of remedying geographic disparities in heart transplantation for

Donor Heart Allocation

41

http://dx.doi.org/10.5772/intechopen.74819

Therapeutic escalation has been a concern with the current system and will likely continue to be a concern with new allocation systems. Some have postulated that some centers will utilize temporary mechanical support in clinical scenarios that previously were treated with medical bridging (inotropes) or durable mechanical circulatory support in an effort to prioritize their patients. Despite stricter requirements for data and verification, no system will be able to prevent behavior aimed at simply improving the chances of heart transplantation by choosing one therapy over another. Further comparing the transplant needs of a patient on ECMO with a patient with a total artificial heart/durable biventricular support is difficult; given the initial condition may have been cardiogenic shock for both patients. Similar patients may be treated differently in centers with implications for transplant access that is the result of the center choices not patient acuity- a difference that is hard to incorporate into

The 2018 UNOS allocation system is rooted in the 2006 allocation reflects the evolution of the practice of heart failure since explosion of mechanical circulatory support. This next iteration of the allocation system focuses on present era mortality rates among like pools of candidates and seeks to improve regional sharing for more acute patients. It seeks to reduce waiting list mortality rates by allocating organs to the most critically ill candidates, rectify issues with specific patients groups, and incorporate broader geographic sharing to optimize access and limit regional disparities while keeping post-transplant survival (within each status) comparable to the current system. Future allocation systems will likely evolve toward a global heart

\*, Mohammad Choudhary<sup>1</sup> and Scott C. Silvestry<sup>2</sup>

2 Florida Hospital Transplant Institute, Orlando, Florida, United States

1 Downstate Medical Center, Division of Cardiothoracic Surgery, State University of

\*Address all correspondence to: louis.stein@downstate.edu

New York, Brooklyn, New York, United States

acutely ill patients?

allocation policy.

6. Conclusion

allocation score.

Author details

Louis H. Stein<sup>1</sup>

Table 2. 2006 status with 2018 status and corresponding indications. The duration of listing varies by indication. 1: Renewable every 7 days. 2: Renewable every 14 days. 3: Discretionary 30-day period. 4: If Status 1 is not renewed. 5: If Status 2 is not renewed. 6: 14 days if clinical evidence of driveline infection, 42 days if bacteremia requiring antibiotic, 90 days if device pocket infection or recurrent bacteremia. 7: 14 days if two hospitalizations in 6 months, 90 days if 3 times in past 6 months. 8. Renewable every 90 days 9. 180 days.

The current practice of combined organ transplant involving Heart-Lung or Heart-other is inconsistent at best. Patients for combined organ would be listed at a minimum as status 5 but the majority of patients would qualify for higher status. The actual allocation of combined thoracic/thoracic-abdominal organs is inconsistently applied and varies from OPO to OPO despite policies aiming to clarify this practice. Current efforts within the transplant community seek to standardize these practices.

Although the geographic distribution of organ offers has been addressed in the 2018 paradigm, the exact unit of correction is unclear. Equal 500 mile circles do not yield equal access to potential organ offers. Should geography be indexed to population? Should the number of transplant centers encompassed by these widening circles be factored into this algorithm? Further, all Organ Procurement Organizations do not perform equally, with regional, cultural, and religious differences contributing to willingness to donate as well as inherent differences in OPO practices and efficiencies. Should geography be indexed to create equal access in potential organ offers? Lastly organ acceptance varies greatly from program to program [16]. By offering wider circles of potential organ offers, is the new system incentivizing conservative acceptance practices instead of remedying geographic disparities in heart transplantation for acutely ill patients?

Therapeutic escalation has been a concern with the current system and will likely continue to be a concern with new allocation systems. Some have postulated that some centers will utilize temporary mechanical support in clinical scenarios that previously were treated with medical bridging (inotropes) or durable mechanical circulatory support in an effort to prioritize their patients. Despite stricter requirements for data and verification, no system will be able to prevent behavior aimed at simply improving the chances of heart transplantation by choosing one therapy over another. Further comparing the transplant needs of a patient on ECMO with a patient with a total artificial heart/durable biventricular support is difficult; given the initial condition may have been cardiogenic shock for both patients. Similar patients may be treated differently in centers with implications for transplant access that is the result of the center choices not patient acuity- a difference that is hard to incorporate into allocation policy.
