New children's heart valve

Feb 16 2006

New valves and stents made of super-elastic, shape-memory metal alloy combined with less invasive procedure mean quicker recovery for children with heart disease.

Children with congenital heart defects may soon have an alternative to invasive open heart surgery that will mean less time in the hospital, a quicker recovery and no need to break open the breastbone, thanks to a new collaboration between researchers at the UCLA Henry Samueli School of Engineering and Applied Science and pediatric cardiologists at Mattel Children's Hospital at UCLA.

Using a super-elastic, shape-memory metal alloy called "thin film nitinol," UCLA engineers are developing a collapsible heart valve for children that can be loaded into a catheter, inserted into a vein in the groin area, guided into place and then deployed in a precise location within the heart. As the valve is released from the catheter, it springs back to its original shape and begins to function.

"What is really novel about the valve UCLA Engineering has created is the memory retaining alloy and butterfly design that opens or hinges from the middle of the valve rather than the edges," said UCLA mechanical and aerospace engineering professor Gregory Carman, who, along with UCLA researcher Lenka Stepan, crafted the valve. "The unobtrusive leaflets within the valve mean there is no obstruction to blood flow. This smaller, low-profile design is well suited for children and, over time, will potentially allow children born with heart valve defects to experience less pain and live much fuller lives."

Dr. Daniel Levi, assistant professor of pediatric cardiology at Mattel Children's Hospital at UCLA, designed the valve and joined Carman and Stepan to create and develop the revolutionary new device.

"Using catheters and collapsible valves, heart valves can be replaced without stopping the heart, without cutting the chest open and without long recovery times," Levi said. "This will represent a huge improvement in care for children living with a very difficult condition."

A defective heart valve fails to fully open or close, letting blood leak back into the heart chamber. This condition most often is treated surgically, and the valve is replaced with a human donor valve, a porcine valve or a mechanical one. All heart valve replacements have a limited life span and must be replaced eventually, but for children, there are even greater complications: the valves do not grow as children grow, which could mean as many as three or more open-heart surgeries during childhood and adolescence alone.

Open-heart surgery typically requires three to four days in intensive care, at least one or two weeks in the hospital and a lengthy recovery period at home. In contrast, patients who have valves replaced via catheter could go home as early as the following day, with little pain.

While catheter-based valve replacement procedures already are revolutionizing valve replacement for larger patients, smaller children have not yet benefited from this technology. Although many companies are competing to develop the ideal transcatheter heart valve, most of these valves are bulky and can be used only in adults. Thin film nitinol could allow doctors at UCLA to make a transcatheter heart valve suitable for use even in small children.

"By collaborating with UCLA Engineering, we are creating a pediatric heart valve that has great strength and biocompatibility. It could mean a shortened procedure, a lower level of risk, and much less stress on the patient and their family. It also will mean a lower cost to the health care system," Levi said. "Our valve is presently being designed for replacement of the pulmonary valve, but eventually may also be able to be used for the aortic valve."

The UCLA team also has used thin film nitinol successfully in other biomedical applications such as stents -- short narrow metal mesh tubes inserted into an artery or bile duct to keep blocked passageways open -- as well as in other applications.

"Although the medical community has used bulk nitinol for the past decade in stents and other implantable biomedical devices, thin film nitinol has yet to be incorporated into a commercially available biomedical device," Carman said.

"Recent studies we've conducted have shown that thin film nitinol can be used to cover stents and to provide a barrier in preventing regrowth of tissue into stented arteries and veins. Beyond its use in either percutaneously or surgically placed valves, I anticipate that thin film nitinol will have a wide variety of applications in the development of future implantable biomedical devices for both adults and children," Levi added.

In order to bring their new valves and stents for children to market, UCLA's Mattel Children's Hospital and researchers at UCLA Engineering are seeking to collaborate with industry, but both Levi and Carman say it will still be a number of years before the valves will be commercially available.

To date, the research done by Carman and Levi has been supported by a grant from the National Institute of Child Health and Human Development, part of the National Institutes of Health. Thin film nitinol originally was developed for defense applications with support from both the Air Force Office of Scientific Research and the Defense Advanced Research Projects Agency.