This fall, a clinical trial at Boston Children’s Hospital will use patients’ own umbilical veins instead of plastic tubing for Blalock shunt operations on patients with
Clots in Blalock shunts pose a serious threat. “All of the blood flow to the lungs is dependent on that shunt staying open,” says Sitaram Emani, MD, who is leading the trial along with his colleague David Hoganson, MD.
If there is a clot, the blood oxygen level can drop so low that the infant needs emergency surgery to survive. “We now know clots occur more often than we thought — up to 20 percent of newborns have some form of clotting,” says Emani. “That’s why we’re so meticulous about using blood thinners.”
But of course, blood thinners have their own risks.
“When you're essentially poisoning the whole system with anti-clotting agents,” Emani explains, “blood in places where it’s supposed to clot doesn’t clot.”
A vein of hope
That’s where the umbilical vein comes in.
Like all blood vessels, the umbilical vein is lined with endothelium, a protective layer that helps blood flow smoothly through the vessel without clotting. Furthermore, umbilical veins can be set aside at birth and stored for later surgical use in a special device that provides nutrients.
“We have proven that not only can we get usable vein (with endothelium) from the cord at the time of delivery, but we can keep that tissue alive long enough to be used in single ventricle surgery, which is typically four to five days after birth,” says Emani. He and Hoganson presented these results at the American Association for Thoracic Surgery Annual Meeting this spring.
Emani and Hoganson also proved that the preserved veins were clot-resistant and were strong enough to withstand the mechanical pressure of blood circulation in the body.
Umbilical veins can be adjusted for size by placing an adjustable stent on their outside, which has no direct contact with blood. “We can then go back in when the child is a little bigger, and balloon-dilate the stent to expand the tissue,” explains Emani.
The hope is that preserved umbilical veins can be used in a variety of cardiac interventions. Emani predicts they may be useful to treat pulmonary atresia, aortic valve disease or any condition that requires reconstruction of valves or arteries in newborns.
“This is really just the beginning in terms of using placental and umbilical tissue for cardiac reconstruction,” he says.