TUESDAY, Jan. 18, 2005 (HealthDayNews) -- Belgian researchers are reporting a successful first trial that could change the definition of a stent -- the metal tube that is implanted to keep an artery open.
Current stents are implanted permanently to prevent an artery from closing again. But the researchers said they have used a metal stent that is absorbed by the body in a matter of weeks. And this stent does a better job of keeping arteries open than the permanent kind, the scientists added.
"The stent we use is 90 percent magnesium, which you find in normal blood and normal tissue," said Dr. Marc Bosiers, head of the department of vascular surgery at A.Z Sint-Blasius Hospital in Dendermonde. The other 10 percent is made up of rare earth elements. Eight years of animal tests and a trial with 20 persons have shown that the body starts absorbing the stent within a week to 10 days, and the stent is completely absorbed in no more than 60 days, he said.
The human trial also showed that a larger percentage of arteries that received the absorbable stent remained open six months later than the reported success rate with conventional stents, Bosiers said.
The researchers presented the findings Jan. 18 at the 17th International Symposium on Endovascular Therapy in Miami Beach, Fla.
The people in the trial all had severely blocked arteries below the knees, a condition called peripheral arterial disease that can lead to amputation. Six months after the implant, long after the stents had been absorbed, 15 of 19 arteries remained open. (One patient died of pneumonia unrelated to the procedure.) Typically, only 40 percent of below-the-knee blocked arteries remain open six months after a conventional stent has been implanted, Bosiers said.
Why should a stent that is absorbed by the body do better than one that remains in place? A permanent stent can cause chronic inflammation and damage to the blood vessel wall that induces growth of new tissue that eventually re-blocks the artery, Bosiers said.
The absorbable stent "does not stay long enough to be an inducer of chronic inflammation," he said. "You only need [an absorbable] stent for 10 to 14 days, but a conventional one must stay in the body for the rest of your life."
The trial reported at the meeting "was a first study to look at safety and efficacy," Bosiers said. "If the material is absorbed in the vessel wall, where does it go?" Extensive blood and tissue tests found that "nothing toxic was to be seen," he said.
The Belgian researchers are now initiating two large-scale trials designed to get regulatory approval for use of the absorbable stent in European medical practice, Bosiers said. One trial of treatment of below-the-knee arteries is being done at 10 European high-volume centers. The other will use the stent in blocked coronary arteries, he said.
"If we have a positive outcome in the below-the-knee study, we could go commercial with the stent in Europe at the beginning of 2006," Bosiers said. "We will be starting parallel studies in the United States by the end of the year. In these things, Europe is always a little bit ahead because the regulations are not as strict, but we hope to go commercial in the United States by 2007."
Dr. Deepak L. Bhatt, director of the interventional cardiovascular fellowship program at the Cleveland Clinic Foundation, said the trial results are "only a proof of concept, but a very important proof of concept. This is very likely to be the future of stenting. If it pans out, it will be a major advance."
The below-the-knee results are exciting because "right now we don't have great therapies for that sort of patients," Bhatt said. But an absorbable stent would have uses all over the body, because there are many cases in which a patient needs stenting but one cannot be implanted because it might interfere with treatment of later problems, he said.
Current stents are coated with drugs to prevent clotting. "Our next step will be to combine an active coating on a bioabsorbable medium," Bosiers said.
That prospect could truly expand the definition of a stent, Bhatt said. "We would be at a whole new level where a stent becomes a drug-delivery system," he said.
Learn more about stents from the American Heart Association.