The days of performing open-heart surgery to replace defective
heart valves may soon be coming to a close, thanks to the ongoing
development of a transcatheter collapsible heart valve by UCLA
researchers.
The new valve may one day enable researchers to insert a
catheter into the groin area of the patient and channel the valve
to the heart area, where it will be implanted and resume the form
in which it was originally designed.
This procedure would be done instead of traditional open-heart
surgery, which involves the risky procedure of cracking open the
patient’s breastbone.
Researchers on the project have been focusing on the
valve’s use in pediatric cardiology, an area they say is
largely overlooked by other researchers.
Dr. Daniel Levi, assistant professor of pediatric cardiology at
Mattel Children’s Hospital at UCLA and a researcher for the
project, said the valve they are designing is specifically for
smaller patients, predominantly children born with heart
defects.
Levi said it is possible, though less common, for children to
have acquired valve problems due to infection or disease, as many
adults have.
Heart valve problems can lead to heart failure, as incomplete
valve closure causes blood to leak back into the heart chamber,
making the heart work harder to pump blood out. The extra energy
expenditure can leave patients tired. Children with valve problems
often have inadequate amounts of oxygen in their blood and
increased respiratory problems.
Dr. Thomas Klitzner, division chief of cardiology at Mattel
Children’s Hospital, said that until surgery can be performed
the only options for treatment are medications designed to make the
heart beat stronger and pump blood more effectively to increase
blood flow to the lungs and rest of the body.
But this treatment can only do so much.
“Medicines are helpful, but they’re not nearly as
effective as interventional purposes (such as surgery),” he
said.
Klitzner said the youngest patient he has seen receive heart
valve surgery in 25 years of medical work was 5 months old.
Levi said the ultimate goal is to create a valve that does not
require open-heart surgery, which involves stopping the heart,
making a large incision that may leave a scar, and cracking open
the breastbone, which puts the patient at greater risk for
infection.
But even this new valve is not the same as having a properly
working heart valve.
“This is not the kind Mother Nature makes, but the point
is it’s a lot less invasive to place this valve,” Levi
said. “The key will be to build a valve that we can put in
with a catheter as good as the one with surgery. We don’t do
the patient any good unless our valve is as good.”
Levi said the “special” thing about this particular
heart valve is nitinol, a material composed of nickel and titanium
and similar to rubber in its elasticity.
Greg Carman, a mechanical and aerospace engineering professor at
the UCLA Henry Samueli School of Engineering and Applied Science
and researcher for the project, said his lab is able to provide
access to thin-film nitinol about 5-10 microns thick, which is
about 1/10th the thickness of a human hair. This gives researchers
the ability to make valves able to fit into a catheter.
Carman said a protective coating is applied to the nitinol to
prevent the material from harming the body. Nitinol is already used
as material for making stents, which are tubes that provide support
for heart blood vessels.
Lenka Stepan, a fourth-year biomedical engineering graduate
student and researcher for the project, said they are continuing to
work to make the valve more durable and go through several
blood-flow cycles without deteriorating.
Along with the benefits of nitinol, researchers said the less
invasive nature of a catheter procedure is one of its main appeals.
Children often go through a series of procedures to replace the
valves as they outgrow them or as the valves wear down.
Klitzner said going through repeat procedures poses many dangers
to patients.
“The danger of the initial surgery depends on how sick the
child is from the underlying condition. With subsequent surgeries
(there is an) increased difficulty of taking out a foreign
structure once scar tissue is formed and there’s been the
formation of new blood vessels which can cause extra time to get
the valve out and extra bleeding,” he said.
But researchers hope the new valve and it’s less invasive
procedure will minimize these risks.
In addition to the physical hazards of multiple surgeries,
Klitzner said there are resulting psychological and emotional
effects.
“One is the scar (from opening the chest cavity) which for
many children is difficult. They get teased,” he said.
Klitzner said that with a catheter procedure there are several
other advantages, including decreased hospital stay, especially in
intensive care. This decreases the cost associated with heart valve
replacement and frees up hospital beds for sicker patients.
Risks associated with the catheter procedure include blood loss,
infection, entry site pain, swelling and discomfort.