3. The changing land scape of heart failure and issues with the 2006 allocation

The management paradigm and spectrum of potential heart transplant recipients has changed dramatically. In 2006, 1203 patients were listed for transplant rising to 3008 by 2015 [8]. As would be expected in a system prioritizing the most urgent patients, Status 1A have received the majority of heart transplants on an annual basis since 1998. According to the Scientific Registry of Transplant Recipients (SRTR), the number (%) of Status 1A listed for transplant has gone from 660 (34.8% of the waitlist) to 1190 (58.4% of the weight list). In the same time period, the Status 1B has gone from 723 (38.8% of the waitlist) to 743 (3.5% of the waitlist), and Status 2 from 509 (26.9%) to 102 (5.0% of the wait list). (Scientific Registry of Transplant Recipients, 2016) In the same period, Status 1A patients increased from 5–13% of all patients listed. Sixtyseven percent of those who received transplants in 2015 were status 1A; however, those listed as 1A were three times more likely to die while on the transplant waiting list.

With refinement therapy for advanced heart failure the expected clinical course of patients listed as 1A have notably diverged. In particular, Mechanical circulatory support (MCS) technology has dramatically expanded driven by improved survival since prioritization was first established [11]. MCS supported patients now includes a wide spectrum ranging from deteriorating CHF to acute cardiogenic shock, while utilizing a larger range of percutaneous 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 no longer suitable as a dichotomous gage for acuity and transplant listing.

Thoracic Organ Transplantation Committee determined there was too little data to provide an accurate reliable score. Therefore, the committee elected to proceed with a modification of the

Donor Heart Allocation

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

A new prioritization that could better reflect the clinical needs of patients in the present day was needed. Analysis demonstrated that patients supported with continuous flow LVAD (cfLVAD) demonstrated a mortality closer to Status 2 patients than those at Status 1A or B (such as those requiring inotropic therapy [9, 10, 15]. Conversely, mortality has remained high among patients with biventricular support or among patients with LVAD related complications [15]. Analysis of waitlist and post-transplant mortality data was used to construct a "straw man" model [10]. The SRTR utilized thoracic surgery allocation modeling (TSAM) to determine the effects of these changes on the newly proposed Status system, which did not

The resulting system contained six statuses. Much of Status 1 was partitioned to better reflect the candidate's relative urgency as reflected by waitlist mortality data. Status 1A candidates were re-stratified into Status 1–3. Status 4 is roughly equivalent to Status 1B, with the addition of patients who would require exception status to apply for transplantation. The new status

To provide higher acuity patients over a wider region, geographic distribution of organs was restructured. In the revised system, offers would be made to Status 1 patients with in the DSA and Zone followed by Zone B. Status 2 patients would then be extended the offer. These changes strike a balance between broadened access to a precious resource and availability to

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

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.

allocation system with plans for a HAS in a future iteration.

suggest a change in waitlist or post-transplant deaths [10].

policy is presented in Table 2 with its equivalent 2006 status.

5. Unmet challenges and future concerns

exist within the SRTR to develop appropriate offsets.

closer patients of lesser acuity [8].

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 patients within the DSA [8].

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 the transplant candidate cohort.

#### 4. The 2018 system

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 Thoracic Organ Transplantation Committee determined there was too little data to provide an accurate reliable score. Therefore, the committee elected to proceed with a modification of the allocation system with plans for a HAS in a future iteration.

A new prioritization that could better reflect the clinical needs of patients in the present day was needed. Analysis demonstrated that patients supported with continuous flow LVAD (cfLVAD) demonstrated a mortality closer to Status 2 patients than those at Status 1A or B (such as those requiring inotropic therapy [9, 10, 15]. Conversely, mortality has remained high among patients with biventricular support or among patients with LVAD related complications [15]. Analysis of waitlist and post-transplant mortality data was used to construct a "straw man" model [10]. The SRTR utilized thoracic surgery allocation modeling (TSAM) to determine the effects of these changes on the newly proposed Status system, which did not suggest a change in waitlist or post-transplant deaths [10].

The resulting system contained six statuses. Much of Status 1 was partitioned to better reflect the candidate's relative urgency as reflected by waitlist mortality data. Status 1A candidates were re-stratified into Status 1–3. Status 4 is roughly equivalent to Status 1B, with the addition of patients who would require exception status to apply for transplantation. The new status policy is presented in Table 2 with its equivalent 2006 status.

To provide higher acuity patients over a wider region, geographic distribution of organs was restructured. In the revised system, offers would be made to Status 1 patients with in the DSA and Zone followed by Zone B. Status 2 patients would then be extended the offer. These changes strike a balance between broadened access to a precious resource and availability to closer patients of lesser acuity [8].
