Research published in the Journal of the American Medical Association Nov. 12 suggests that, despite the Organ Procurement and Transplant Network’s (OPTN) overhaul of the U.S. heart allocation system in 2018, CV transplant programs still suffer from variability in survival benefit and a lack of standardized guidelines for ranking candidates.
The study, penned by William F. Parker, MD, MS, and colleagues at the University of Chicago, also questioned whether transplant centers exercise too much power over which patients receive donor hearts and which don’t. More than 7,300 patients in the U.S. are on a waiting list for a new heart any given year, but because demand so greatly exceeds supply just 3,200 transplants are performed over the course of those 12 months.
The three-tiered heart allocation system was developed as a means for triaging the thousands of patients who join CV waiting lists each year and is meant to prioritize those who need donor hearts the most. The problem is that, unlike some organ allocation systems that use objective measures to score and categorize patients, the heart system lacks a set of streamlined criteria for categorizing patients, instead relying on a status-based system that ranks people according to the intensity of treatment they’re receiving.
In 2016, the OPTN recognized there were “major problems” with the system, noting the rules seemed to incentivize centers to overuse high-intensity therapies like high-dose inotropes so their patients would achieve priority status for a transplant. Two years later the network rolled out an update to the heart allocation system, expanding the number of status levels from three to six and implementing a cardiogenic shock requirement designed to further restrict access to the top priority status levels.
“Despite the major policy change, the association between transplant center candidate selection and management practices on the effectiveness of the original three-tier heart allocation system has not been well-studied,” Parker and co-authors wrote in JAMA. “Furthermore, the potential benefits of the new six-tier system have not been quantified.”
Parker and colleagues initiated a study of 29,199 candidates on transplant waiting lists at 113 American centers between 2006 and 2015. They focused on the idea of survival benefit—the difference between survival after heart transplant and waiting list survival without transplant at five years—as a primary metric, estimating each center’s survival benefit with a mixed-effects proportional hazards model.
During the study period, 68% of patients underwent a heart transplant, while 27% died or underwent another transplant operation. Sixty percent of the 9,384 patients who didn’t receive a heart transplant died—2,644 while on the waiting list and 3,025 after they’d been delisted.
The authors said estimated five-year survival was similar among transplant recipients—around 77%—regardless of where they underwent surgery. Patients who didn’t receive a new heart saw five-year survival rates of around 33%, reflecting a 44% survival benefit with a successful transplant.
The average survival benefit for centers varied during the study period, ranging from 30% at low survival benefit centers to 55% at high survival benefit centers. Just over a quarter of centers demonstrated an overall survival benefit lower than the mean, while another quarter demonstrated an overall survival benefit higher than the mean. Compared with low survival benefit centers, high benefit centers performed heart transplants for patients with lower estimated waiting list survival rates.
In short, Parker and co-authors wrote, for every 10% decrease in estimated transplant candidate waiting list survival at a center, there was an increase of 6.2% in the five-year survival benefit associated with heart transplant.
‘More loopholes and inefficiencies’
Alexander T. Sandhu, MD, MS, of Stanford University, and colleagues said in a related editorial that while Parker et al.’s results suggest the OPTN’s updated six-tier system did result in some more balance in survival benefit across centers in the U.S., there’s still significant variability. As Parker’s team put it, “adding more tiers and complexity to the therapy-based system may simply create more loopholes and inefficiencies.”
The editorialists argued that transplant centers are still incentivized to overuse therapies like extracorporeal membrane oxygenation and intra-aortic balloon pumps to achieve higher waiting list status—something that might be helped by consolidating transplant programs and reducing regional competition.
“Transplant outcomes may be improved by centralizing this process at hospitals that already perform heart transplants for patients with highest illness severity while demonstrating similar post-transplant survival compared with centers that perform heart transplants for lower acuity patients,” Sandhu et al. wrote. “This type of major reform would encounter important challenges with respect to patient access, development of adequate infrastructure and contracting with payers. However, these challenges may be outweighed by the importance of ensuring optimal donor heart allocation.”
A solid fix, Sandhu and colleagues said, would be developing a continuous risk score that’s able to estimate the expected net benefit of transplant based on a patient’s unique metrics. Allocation scores are used for liver and lung transplants in the U.S., and in Europe a Cardiac Allocation Score is in the works.
“The transplant community owes it to donors and their families to continually improve the organ allocation system to ensure that society is deriving the maximum good from their precious gift of life,” the editorialists wrote.