Senior Staff Writer
Using equations that incorporate height, weight, age, and sex to predict heart mass may better allocate donor hearts to transplant recipients than considering body mass alone, a retrospective study suggested.
Although differences in body mass were not predictive of survival after heart transplantation, differences in predicted heart mass using those equations were related to survival up to 5 years after the operation, according to Robert Reed, MD, of the University of Maryland School of Medicine in Baltimore, and colleagues.
Specifically, patients who received the most undersized hearts had significantly increased risks of dying at 1 year (HR 1.25, 95% CI 1.02-1.54) and 5 years (HR 1.20, 95% CI 1.04-1.39), the researchers reported online in JACC: Heart Failure.
The study also pointed to heart size as an explanation for the worse transplant outcomes seen among men who receive donor hearts from women. Before adjustment, a sex mismatch between the donor and recipient was associated with increased mortality in male patients, but not in female patients. In a multivariate analysis that included predicted heart mass, a sex mismatch was no longer associated with survival in men.
“Differences in donor-recipient predicted total heart mass modulated the survival associated with donor-recipient sex mismatch and identified donor heart undersizing as an otherwise occult and potentially preventable cause of mortality following orthotopic heart transplantation,” the authors wrote.
In an interview, Reed said that incorporating the equations used in the study into the national organ allocation scheme — which he suspects will be done at some point — likely would not affect access to organs.
“All organs harvested are going to go into somebody, and using our algorithm to better match the donor and the recipient will just allow the organs that are harvested to go into people who are more likely to do well with those organs,” he said.
Although the current system for allocating donor hearts considers body weight differences between the donor and recipient, weight has not been strongly related to heart size. Sex has been associated with heart size, however, and previous studies have shown that a sex mismatch between the donor and recipient is associated with poorer outcomes, particularly for male recipients.
To explore the link between predicted heart size and outcomes from heart transplantation, Reed and colleagues performed a retrospective study of 31,634 adults who underwent transplantation using data from the United Network for Organ Sharing (UNOS). Most of the recipients and donors were male (77% and 71%, respectively).
Most of the patients (70.9%) received their new heart from an individual of the same sex.
Based on differences between the donors and recipients in predicted heart mass using the equations that incorporate height, weight, sex, and age, patients who received the most undersized hearts had increased death rates after the operation.
“Specifically, a mismatch involving donor organs with a predicted total heart mass greater than 10% to 15% below that of the recipient’s predicted total heart mass was associated with [a] markedly increased risk of mortality,” Reed and colleagues wrote.
Accounting for differences in predicted heart size eliminated the survival disadvantage for male patients receiving female organs, which “may suggest that the increased risk results from physiological mechanisms,” according to the researchers. “Otherwise stated, the sex-mismatch issue in male recipients appears strictly related to size mismatch alone, and an appropriately sized heart from a female donor performs as well as does a similarly sized heart from a male donor.”
Valluvan Jeevanandam, MD, chief of cardiac and thoracic surgery at the University of Chicago, said that the equations used in the study could be incorporated easily into the UNOS allocation scheme, but said, “In my opinion, the size doesn’t really matter as much as the heart function. What you want to do is be able to deliver a cardiac output to the recipient that’s sufficient for their circulation.”
“So I think … the predicted mass will be an improvement over sheer [body] weight but I don’t think that is the end-all because there are other parameters that one needs to evaluate as well,” he said.
He also cautioned against using the study to disregard the possibility of transplanting undersized hearts altogether, pointing to his previous research showing that good results could be obtained after transplanting pediatric hearts into adult recipients.
The study was supported in part by a Health Resources and Services Administration contract.
Reed is funded in part by the Alpha-1 Antitrypsin Foundation/Chest Foundation as well as the Flight Attendant Medical Research Institute. The other authors reported funding from the National Institutes of Health, the Department of Veterans Affairs, the Veterans Affairs Medical Center Baltimore GRECC (Geriatric Research Education and Clinical Centers), and the National Heart, Lung and Blood Institute.