EXPLANATION


Pediatric patients with refractory heart failure placed on the cardiac transplantation waiting list have significant mortality due to long wait times related to the scarcity of donor organs. Furthermore, a proportion of patients with certain ABO blood types have even longer waitlist times. Specifically, recipients with type O blood have the longest waitlist time and can only receive O-type donor organs because of the presence of both anti-A and anti-B antibodies (isohemagglutinins). The immaturity of the immune system in infants prompted the first incompatible blood type (ABOi) heart transplantations in the 1990s.


Currently, ABOi heart transplants in young children are routinely performed. Reports in the literature indicate that the long-term outcomes of both compatibility groups are similar. In July 2016, the Organ Procurement and Transplantation Network (OPTN) expanded the candidacy for ABOi heart transplantation from patients younger than one year of age to include patients one to two years of age, as well as increasing the isohemagglutinin titers from 1:4 to 1:16 in this age group. After this policy change, a study using the Scientific Registry of Transplant Recipients database demonstrated that the percentage of ABOi transplantations increased by 2.7-fold, and the waiting times decreased by 68% for children listed for ABOi transplants compared to those listed for ABO compatible (ABOc) transplants. The survival rates were similar in children who received an ABOi versus ABOc heart transplant.


In March 2023, the OPTN Executive Committee approved further policy changes, which allowed transplant programs to indicate they were willing to accept an ABOi donor heart and/or donor heart-lung for status 1A and 1B candidates placed on the waiting list before their 18th birthday. Transplant programs must report isohemagglutinin titers equal to or less than 1:16 to the OPTN every 30 days on behalf of such candidates. Previously, candidates had to be registered before their 2nd birthday.


Pediatric status assignments include status 1A, 1B, 2, and inactive. To be listed status 1A, a pediatric candidate must be less than 18 years of age at the time of registration and require therapy with one or more of the following: 1) continuous mechanical ventilation; 2) an intra-aortic balloon pump; 3) a stent or prostaglandin infusion to maintain ductal-dependent circulation; 4) multiple inotropic infusions or a single inotrope at high dose to treat hemodynamically unstable heart failure; or 5) a mechanical circulatory support device. Pediatric status 1A must be recertified every 14 days.


The correct answer is B. The patient described in the stem is 17 years old, status 1A, and has a recent isohemagglutinin titer of 1:32. Although the other criteria set by the most current OPTN policy are met, the isohemagglutinin titer is greater than 1:16. Therefore, this patient is a candidate for an ABOc, but not ABOi heart transplantation.


REFERENCES


Bansal N, West LJ, Simmonds J, Urschel S. ABO-incompatible heart transplantation-evolution of a revolution. J Heart Lung Transplant. 2024. 43(9):1514-1520.


Milligan C, Daly KP. ABO-Incompatible heart transplantation: where science, society, and policy collide. J Card Fail. 2024;30(3):486-487.


Amdani S, Deshpande SR, Liu W, Urschel S. Impact of the pediatric ABO policy change on listings, transplants, and outcomes for children younger than 2 years listed for heart transplantation in the United States. J Card Fail. 2024;30(3):476-485.


Organ Procurement and Transplantation Network. Notice of OPTN Policy Changes. Modify heart policy for intended incompatible blood type (ABOi) offers to pediatric candidates. Updated June 26, 2023. Accessed July 27 2024. https://optn.transplant.hrsa.gov/media/05vnqa0k/optn_heart_aboi-offers_pn_june-2023.pdf


Organ Procurement and Transplantation Network Policies. Updated July 25, 2024. Accessed July 30, 2024. https://optn.transplant.hrsa.gov/media/eavh5bf3/optn_policies.pdf