In a first-of-its-kind study by the University of Maryland’s School of Medicine, new data has come to light that may significantly alter the process of matching donor hearts to a recipient. For decades organ allocation for heart transplantation has used an individual’s body weight as the standard link between donors and recipients. According to new findings published Jan. 8 in JACC: Heart Failure however, while two people may weigh the same, their hearts could have vastly different sizes — often resulting in a smaller donor heart straining to do the work that is required of it.

Additional Resources Heart Failure and Transplant Section CardioSmart for Your Patients: About Heart Transplant CardioSmart for Your Patients: Size Matters for Patients Undergoing Heart Transplantation

The study analyzed more than 31,000 donor-recipient adult heart transplant pairings from the United Network for Organ Sharing (UNOS) transplant registry between October 1989 and June 2011. The study’s comparison of predicted heart mass showed that risk of death rose considerably when the predicted mass of a donor’s heart was 10 to 15 percent below the predicted mass of the recipient’s heart. Those that had the most undersized hearts were 25 percent more likely to die in the first year after transplant. Researchers have dubbed this occurrence as the “Grinch” effect, referring to Dr. Suess’ infamous curmudgeon whose heart was “two sizes too small.”

“Undersizing a donor heart is very dangerous,” says the study’s co-author Keshava Rajagopal, MD, PhD, a University of Maryland heart and lung transplant surgeon and assistant professor of surgery at the University of Maryland School of Medicine. “It’s like putting a motorcycle engine into a truck.” Over the course of the study researchers also found that the inequality between heart mass amplified between genders, with men who receive women’s hearts proving to be 32 percent more likely to die in the first year after transplantation. “This is entirely because of suboptimal sizing,” says the study’s principal author, Robert M. Reed, MD, assistant professor of medicine at the University of Maryland School of Medicine and a transplant pulmonologist at the University of Maryland Medical Center. “Even if the weights of donor and recipient are similar, the female heart is considerably smaller, while women are more often given men’s hearts that are larger.”

With more than 3,700 people worldwide undergoing heart transplantation on a yearly basis, and about 3,570 people currently on the heart transplant waiting list in the U.S., this new research hopes to provide clinicians with a new calculus for better donor-recipient matching and better-functioning hearts. “This study adds an intriguing analysis to the existing data on optimal selection of appropriate donors for patients awaiting cardiac transplantation,” says Mary Norine Walsh, MD, FACC, medical director of heart failure and cardiac transplantation programs at St. Vincent’s Heart Center of Indiana. “Whether or not cardiac size mismatch alone plays a pivotal role in the known suboptimal outcomes for female cardiac transplant recipients and for male recipients of female donor hearts will await further study.”

Keywords: Registries, Waiting Lists, Tissue Donors, Calculi, Heart Transplantation

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