The study was small, with 50 patients. The follow-up lasted 10 years.
The results are called ''excellent'' by researcher Kunihiko Kosuga, MD, PhD, director of cardiology at Shiga Medical Center for Adults in Moriyama City, Japan.
The research is published in the journal Circulation.
The biodegradable stents will eventually replace the current metal stents, Kosuga predicts. A U.S.-based expert says the study findings are positive. However, he doesn't expect the new stents to be on the market anytime soon. "The timeline for U.S. approval would be at least five or six years," says Kirk Garratt, MD, an interventional cardiologist and clinical director of interventional cardiovascular research at Lenox Hill Hospital in New York.
Other companies are already developing biodegradable stents.
More than a million procedures using heart stents are done annually in the U.S. To open the vessel, doctors perform angioplasty. They insert a balloon-tipped catheter into the artery. A stent is collapsed to a tiny diameter and put over the balloon.
When the catheter gets to the blockage, the balloon is inflated to open the vessel. The stent expands and locks into place. The scaffold it forms holds open the vessel.
Clots can form in the stent. Most metal stents are coated with drugs to reduce the risk of clots.
Biodegradable Stents: Study Details
Kosuga's team followed 44 men and six women. The average age was 61. Together, they got 84 stents.
The new stent is made of a cornstarch-based material called poly-l-lactic acid. It completely resorbs in about three years, the researchers found.
The researchers looked for adverse events, such as clots within the stent area. They looked at re-narrowing of the vessels and deaths from heart disease and other causes.
Among the results:
- The survival rate was 98% for heart-related death.
- The survival rate was 87% for death from all causes.
- Half the patients did not have a major cardiac complication.
- Four patients had heart attacks.
- One year after getting their stent, the affected blood vessel had re-narrowed in 16% of patients.
- Two definite clots were found within the stents. One was related to a drug-coated stent implanted close to the biodegradable stent.
Keiji Igaki, PhD, invented and developed the new stent. He is a co-author on the study, but he had no input on the data analysis.
Biodegradable stents are already used in nine European Union countries and Turkey to treat peripheral artery disease. No countries yet have approved the resorbable stents developed by Igaki for heart arteries.
Biodegradable stents cost more, Kosuga tells WebMD. "The cost of manufacturing is about 10% higher than that of the metallic stent," he says.
Biodegradable Stents: Perspective
"These stents actually look safe," says Vincent Bufalino, MD, a spokesman for the American Heart Association and director of cardiology at Advocate Cardiovascular Institute in Chicago. The new report, he tells WebMD, ''gives us some comfort and a long view of these patients."
However, he says, the rate of re-narrowing found, 16%, is about twice that of metal drug-coated stents.
If the biodegradable stent becomes available, it could reduce the need for the blood-thinning drugs used now, Garratt says.
With the metal stents, "we think the blood clot risk falls off fairly steeply after two or three years. It's not clear if the risk ever goes to zero," Garratt says.
Garratt has served as speaker for Abbott Vascular and for Boston Scientific, which also makes heart stents.