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ORLANDO -- The key to expanding the pediatric donor heart pool may be thinking about the problem on an entirely different plane, researchers here said.
Jonathan Plasencia, a PhD candidate at Arizona State University in Tempe, and colleagues, used CT and MRI images to create a three-dimensional reconstruction of donor heart for a "virtual transplant" to see if the size matched.
They then expanded that idea to create a "healthy heart library" where virtual reconstructions of healthy hearts are catalogued by size, and doctors can see if a prospective donor is a size match for their recipient.
Action Points
- Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
The presentation was part of a featured news conference at the American Heart Association meeting.
"If the heart matches the same size for what we want to do with our virtual transplant, we can do that, or we can scale based on volume size," Plasencia said in an interview with ľֱ. "We don't need to stay on a 2-D image plane -- we can move to a 3-D image plane now with engineering tools and start to consider assessment better."
Currently, size-matching strategies for donor hearts are done by weight of the recipient, but they do not take into account if the donor is overweight or underweight, or if the measurements of the donor heart will actually fit into the thoracic cavity of the recipient. To get around this, doctors will skew the weight range they list to the (UNOS) by doing a cardiothoracic ratio from an x-ray image.
, president of the American College of Cardiology (ACC), said that potential size mismatch is an issue not just in the pediatric population, but the adult population.
"They have it pretty well developed -- taking 3-D reconstructions and doing overlays to try to estimate the transplant to body mismatch," he said.
Pediatric transplants generally have restrictions for donor to recipient body-weight ratio of 0.75-3.00 times the recipient weight in infants ≤18 months and 0.75-1.50 times the recipient weight in children >18 months. Using the healthy heart library for three case studies, Plasencia's group found that by taking donor heart volume into account, the "ideal" donor ratio was actually 2 to 3.5 times the recipient weight.
In one case, a newborn with dilated cardiomyopathy received a heart that he would not have been able to receive, as it was from a donor 3.5 times his weight ratio, which is outside the acceptable range.
, medical director of transplantation at Children's National Health System in Washington told ľֱ that about 40% of hearts in this country do not get used because of worries about a size mismatch, and a third of patients die waiting for a heart.
"This kind of a library may allow us to say 'OK, we have a kid with a 7-cm heart, we could safely take a much bigger donor,'" she said. "The ultimate goal would be to maximize the use of our donors, because there's definitely viable donors that we don't use because we can't match them, so this could be one more way to do it."
Plasencia said the library is small with only about 50 data points and with a patient weight range of 22.5-100 kg (about 50-200 lbs), but they hope to continue expanding it.
"We'll minimize the discard of well-functioning organs, and because we're not throwing away good organs, we reduce the wait list or ratio to mortalities," he stated.
Disclosures
Plasencia and co-authors disclosed no relevant relationships with industry.
Primary Source
American Heart Association
Plansencia J, et al "Expanding the donor pool in pediatric heart transplant with a novel three dimensional technique" AHA 2015; Abstract 17469.