ABO-incompatible heart transplants in children aged 2-9 years: A new paradigm in transplant?

Pediatric heart transplantation remains hampered by the limited availability of donor organs. The introduction of ABO-incompatible (ABOi) heart transplantation for infants in the early 2000s expanded the donor pool for individual candidates. Nonetheless, concerns remain about ABOi heart transplantation in children aged over 2 years, and it has not been routinely adopted. At our center we have considered candidates aged 2-9 years for ABOi donors if isohemagglutinin titers were 1:32 or less. We report the outcomes of those who received an ABOi heart transplant. Furthermore, as all transplant-listed children in this age group were tested for isohemagglutinins, the potential for ABOi transplant was investigated.

Data were retrospectively analyzed from all pediatric heart transplants undertaken at our center between 1st January 2013 and 1st June 2023. Primary outcome measures were anti-A and/or anti-B titers at listing and whether an ABOi transplant was performed. Secondary outcome measures were survival and incidence of rejection.

Sixty-two children 2-9 years of age (median age 5.1 years) underwent heart transplantation during the study period. One patient was blood group AB; of the remaining 61 patients, 51 had anti-A and/or anti-B titers measured whilst listed for transplant. Of these, 44 (86%) had isohemagglutinin titers of 1:32 or less at the time of listing, and this dropped to 40 (78%) by the time of transplant. Over the study period, 14 children (age range 2.5-8.9 years, median 4.3 years) underwent ABOi transplant; all 14 patients were well at follow-up with median follow-up time of 4.9 years, range 1.7-8.9 years.

Our data suggests that ABOi heart transplantation is a safe and effective option for older children, at least to 9 years of age. Furthermore, we have shown that the great majority of young children have isohemagglutinin titers in the range that ABOi transplant could be considered. These findings may have a substantial impact on donor availability worldwide. Further work is needed to see if the age range can be extended further.