Children who need heart transplants can spend months or years waiting for a suitable donor heart. Fortunately, the pediatric cardiology team at Lucile Packard Children’s Hospital Stanford has a new strategy for shortening the wait.
The technique enables children to accept larger donor hearts than doctors would have considered for them in the past. Traditionally, heart transplant teams made size-matching decisions on the basis of total body weight and height, but this method left children with few options.
"Unfortunately for smaller children, there are more donor adolescent and adult hearts because they are more likely to get in accidents," said pediatric cardiologist John Dykes, MD.
However, many children who need transplants can safely receive a larger heart than height- and weight-based matching suggests. There are two reasons, Dykes explained: Kids in heart failure stop growing, so their hearts are bigger than their heights and weights imply. And the disease process in many forms of heart failure causes the heart to expand far beyond its normal dimensions. Measuring the actual volume of the heart would work better, the team realized.
So, to help figure out which donor hearts might work for an individual recipient, Dykes and his colleagues are comparing CT scans of donor and recipient hearts, which they process with software made by a Silicon Valley-based company called TeraRecon to estimate heart volume.
"The logistically complicated part is, at the time of the donor offer, how do we CT scan and measure the donor’s heart in real time?" Dykes said. Key to the effort is Stanford’s 3D and Quantitative Imaging lab, whose staff respond around the clock to offers of donated organs. Over the last year, Dykes has been establishing a process for obtaining the scans needed from the organ procurement organizations, the groups that manage organ donation offers.
"If they file a CT scan to our 3D lab, we can put it in [the software], do a quick estimate of the donor’s heart size, and in 15 minutes we have a total cardiac volume that we can compare with the recipient," Dykes said.
The Stanford team is also using data they’ve collected on children awaiting transplant to better understand how the dimensions of the heart change in different forms of heart failure.
Meanwhile, for individual patients, the comparison is "like a virtual transplant," Dykes said. The surgeon looks carefully at images and volume estimates for both hearts to see if there would be room to close the patient’s chest at the end of the surgery.
"We want to make sure the total cardiac volume of the donor is less than the recipient," Dykes said. The new process takes a bit more effort than the old height- and weight-based method, but he says everyone involved knows it's worthwhile. "They understand that what we're trying to do is place the organ safely," he said.
Image of a patient's heart from volume estimation software courtesy of Stanford's 3D and Quantitative Imaging Lab