Vanishing Devices: Doctors implant disappearing stents, heart patches
Novel heart devices fashioned primarily from materials that the body can absorb or break down have made their debut in patients.
This week, cardiologists presented the first clinical studies of two such devices at a conference on cardiovascular therapies in Washington, D.C. The body absorbs most of one novel implant, a patch that can fix heart defects, and it degrades the other, a stent that can prop open a narrowed artery.
The vanishing implants offer potential advantages over permanent materials, which can trigger dangerous clots and impede the body’s natural healing process.
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In one study, interventional cardiologist Michael J. Mullen of the Royal Brompton Hospital in London and his colleagues treated people who had a defective opening in the central wall of the heart. Such defects can contribute to strokes (SN: 2/19/05, p.119: http://sciencenews.org/articles/20050219/bob8.asp).
Mullen’s team used an experimental patch to plug the opening in each of 57 volunteers. The device, manufactured by NMT Medical of Boston, is composed of a cobalt-alloy frame that’s covered with sheets of collagen. Tissue grows over the device, sealing the hole and absorbing the collagen. That makes a more natural patch than existing devices, which use sheets of synthetic material.
Six months after the procedure, 96 percent of the volunteers had no remaining sign of the defect, Mullen reported at the meeting and online on Oct. 24 in Circulation. No serious side effects occurred.
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Cardiologist Horst Sievert, director of the CardioVascular Center Frankfurt in Germany, says that bioabsorbability “is the major breakthrough of this technology.”
In a separate study, interventional cardiologists in New Zealand and Europe have implanted degradable stents into 30 patients who had developed dangerously narrow coronary arteries.
Currently, doctors treat such patients with metal stents, which are mesh tubes that prop open arteries.
The danger of an artery renarrowing lasts only about 6 months after a procedure, says study leader John A. Ormiston of the University of Auckland in New Zealand. So, an implanted metal stent, he says, “is a permanent solution to a temporary problem. It’s like a cast on your arm after [a broken] bone has healed.”
That’s a concern because blood clots, which can cause heart attacks, sometimes form on old stents.
The new stent is made entirely of polylactic acid, a polymer. That substance gradually degrades into lactic acid, which the body metabolizes naturally. Abbott Laboratories of Abbott Park, Ill., owns the stent and supported the study.
No major side effects occurred within a month after stent implantation, and the devices propped arteries open nearly as well as metal stents do, Ormiston says. His team plans to track the volunteers’ health for 2 years. It will take the stents 2 to 3 years to disappear, he says.
Further studies need to ensure that a biodegradable stent can permanently reverse artery narrowing, says Raimund A. Erbel of the West German Heart Center Essen in Germany. If so, he says, this type of novel device “is the way of the future.”