Developing an Absorbable Heart Stent

Novel Design Could Prevent Blood Clot Formation That Plagues Current Stents

From the WebMD Archives

March 26, 2007 (New Orleans) -- The first stent designed to be absorbed by the heart's arteries could overcome a potentially fatal flaw associated with those currently used to prop open clogged arteries, researchers report.

The biodegradable stent, which dissolves over time, appears to prevent the formation of blood clots -- a major concern with the popular drug-coated stents now in use, says Patrick Serruys, MD, a professor of interventional cardiology at Erasmus University in the Netherlands.

In the first small study to test the device, "early results indicated it is safe, effective, and easy to deploy," he tells WebMD.

None of the 26 people implanted with the new stent died, developed a blood clot, or needed a repeat procedure to open a reblocked artery. One person suffered a mild heart attack.

The study, funded by Abbott Laboratories, a maker of stents, was presented at the annual meeting of the American College of Cardiology.

Clots Plague Drug-Coated Stents

Stents coated with drugs to keep arteries from reclogging after being opened in a balloon angioplasty procedure have revolutionized heart care.

In a simple angioplasty, a tiny balloon at the end of a long tube is threaded through an artery in the groin. The doctor shimmies the probe up through the patient's leg and into the arteries of the heart, inflating the balloon at the spot where the vessel has narrowed.

The balloon stretches open the walls of the vessel. Then the balloon is deflated and removed. In about 25% or 30% of patients, the arteries close up again.

To keep the vessel open, doctors now often add a stent to the end of the balloon catheter. The mesh-like metal tubes prop open clogged arteries and restore blood flow. Stents bring the rate of renarrowing down to about 15% to 25%.

In recent years, stents have been coated with a polymer that slowly releases a powerful drug to keep scar tissue from forming.

Unfortunately, the drug also slows the healing process. That's a problem because until the stented blood vessel heals, there's a risk of blood clotsup to two years later that can trigger heart attacks.

Of the 1 million Americans implanted with stents each year, about 80% to 90% now get drug-coated devices, according to the American Heart Association.

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Stent Made of Biodegradable Polyester

The new stent is made of a biodegradable material that slowly releases the drug everolimus to prevent blood vessels from reclogging. Everolimus is not FDA approved for use in the U.S.

Serruys says its design eliminates two possible causes of blood clots: the metal scaffold and the polymer coating.

There are other potential advantages as well. Because the stent is absorbed over time, it may be easier to take MRI or CT images of the stented vessel so doctors can monitor for problems. Also, it will be easier to perform new stenting procedures on the same vessel, he says.

Most importantly, it’s a more natural process, Serruys says.

"When you put a metal cage in a vessel, the fate of the vessel is doomed. It [the stent] controls the size of the vessel, which can never get bounce back and get bigger.

"With the absorbable stent, you have natural healing, and the flexibility of the vessel returns," he tells WebMD.

Studies in animals show that the stent is fully absorbed by the body in 12 to 18 months. Though it is not yet known how long it will take to dissolve in humans, Serruys suspects it will take about two years.

The stent has already been redesigned to make it stronger, Serruys says. Studies using the new device will begin later this year.

Serruys says he has no doubt the stent will eventually be on the market, although it may take years. "This is the beginning of a new era. I am convinced."

Absorbable Stent a Welcome Option

Though more study is needed, doctors say an absorbable stent could prove a welcome option.

"Given the whole question of late-stage blood clots associated with drug-eluting stents, there is a lot of interest in making changes," says Spencer B. King, MD, head of interventional cardiology at Piedmont Hospital in Atlanta.

"If the metal goes away ... it’s certainly possible you’ll have fewer problems," he tells WebMD.

WebMD Health News Reviewed by Louise Chang, MD on March 26, 2007

Sources

SOURCES: American College of Cardiology 56th Annual Scientific Session, New Orleans, March 24-27, 2007. Patrick Serruys, MD, professor of interventional cardiology, Erasmus University, Netherlands. Spencer B. King, MD, chairman, interventional cardiology, Piedmont Hospital, Atlanta.

© 2007 WebMD, Inc. All rights reserved.

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