Pediatric donor hearts are in short supply, especially for infants and small children, because few children die in situations where organs can be donated. Matching requires consideration of several factors, including geographic location, immunocompatibility, and body size of the donor and recipient. This matching system is intended to work fairly, giving priority to transplants to sicker children.
The current waiting list relies on several factors to rank a child and uses only three categories of urgency. The most urgent status is 1A, then 1B, then 2. Factors used to determine a child's category include the type of heart disease the child has (congenital heart disease present at birth or heart disease, which is a heart muscle problem that usually develops after birth). symptoms, etc.) and medications you are receiving.
The research team analyzed data on all 12,408 infants and children under 18 who underwent heart transplantation in the United States between January 20, 1999 and June 26, 2023. To see if the current waiting list system is working as intended, the researchers used statistical techniques borrowed from economics that are typically used to study markets.
“From an economics perspective, we look at this fundamentally as an allocation problem,” Swett said. “We have a scarce resource in the form of donor hearts, and we want to make sure we get it to the candidates who can make the most of it. For pediatric heart transplants, waiting mortality rates are extremely high. So we usually want to prioritize sicker patients.”
The research team investigated how transplant candidates are actually ranked on waiting lists and how candidates would be ranked if the order of the list was based on medical urgency. compared.
We also considered whether improvements in waitlist outcomes were chronologically consistent with allocation changes implemented in 2006 and 2016 that were aimed at creating more equitable waitlists.
Waitlist categories not working as expected
One reason that the likelihood of death on the waitlist decreased during the study period is that the health status of children on the waitlist has also improved in recent years. They are less likely to receive support from a ventilator or extracorporeal membrane oxygenator during transplant. (works like a heart-lung machine) or kidney dialysis, the study found.
However, the medical conditions of children in each of the three waiting list categories varied widely. In fact, the study found that these three categories showed significant overlap in mortality risk. In other words, some critically ill children were classified as priority 2, while other less sick children were classified as 1A status. This means that a heart donor may be offered in place of a child who is less sick.
The study also found that because the three waiting list categories were so broad, sicker children in the same category were sometimes offered their hearts before sicker children because of longer wait times. It is stated here.
We have a rare resource in the form of donor hearts, and we want to make sure we give it to the candidates who can make the most of it.
Experts agree that long wait times should not determine transplant priority. “This could encourage programs to list patients early to allow for wait times,” Almond said.
Surprisingly, the researchers found that changes to waiting list rules in 2006 and 2016 were not associated with rapid improvements in mortality rates, as would be expected if rule changes promoted improvements. I discovered it.
Rather, mortality rates have gradually decreased since 1999. This includes advances in ventricular assist devices (mechanical pumps that support a child's heart while waiting for a transplant) and medical improvements such as increased awareness of when to register a child as a transplant candidate. contributed. Over time, the researchers found that differences in outcomes between patients of different races decreased, and that change translated into improved overall outcomes.
During the study, doctors also realized that organ transplants are safe in infants whose immune systems are still immature, even if their blood types are mismatched. Studies show that phasing in this practice reduces waiting mortality for the youngest patients seeking heart transplants, especially infants with blood type O, who were previously the most difficult recipients of heart transplants. It turned out that.
The study results suggest that waiting list systems should be revised to take into account a wider range of medical factors than currently thought, such as kidney function, liver function, and whether the patient is malnourished, using a combination of factors. This suggests that you need to make an allocation. The authors say each child will be given a numerical risk score that will replace the current three categories.
“The important thing is to be able to aim for and improve the allocation score on an ongoing basis and take into account the innovations that are happening in patient care over that time,” Swett said.
Almond said the revisions should also consider whether patients are healthy enough to benefit and recover from a transplant. It would give priority to the children most in need, who have the best chance of recovering from major surgery.
“This is very difficult because if a patient is on full life support and their organs are failing, they are in critical condition and may not survive the waiting list period. And if you get a transplant, you might not have a good outcome because you have the same risk factors,” Almond said.
In September 2023, UNOS will have a new lung transplant allocation system It will be based on continuous scoring, and the organization is drafting similar systems for other organs. that plans Proposals on how to allocate hearts should be ready for consideration in 2025.
“Finding a way to do this well is very complex, but there still seems to be room for improvement,” Almond said.
Researchers from Stanford University's Department of Pediatrics and Cardiothoracic Surgery, Stanford University's Department of Economics, and the University of Texas Southwestern Medical School contributed to the study.
No funding was received for this study.
