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Advisors to the Food and Drug Administration have been meeting today to discuss problems with the latest technology to keep blood flowing to the heart. They're talking about a kind of stent that was developed several years ago. Like older stents, it's used to keep an artery open once doctors have unblocked it. So far, the doctors have said that the new stents, which are coated with drugs, increase the risk of blood clots. But there's no evidence that people with the coated stents are more likely to have a heart attack or die.

NPR's Jon Hamilton reports.

JON HAMILTON: New technologies have done a lot to help patients avoid coronary bypass surgery, but each advance has brought its own problems. Michael Domanski is a cardiologist at the National Institutes of Heath. He says more than 20 years ago doctors discovered they could thread a tiny balloon through the arteries to reach an area that was blocked.

Dr. MICHAEL DOMANSKI (National Institutes of Heath): The idea was to try without opening someone's chest to get the same effect and, in fact, it's been hugely successful.

HAMILTON: But early on, doctors realized this technique of balloon angioplasty wasn't perfect. Ray Gibbons is a cardiologist at the Mayo Clinic and president of the American Heart Association.

Dr. RAY GIBBONS (American Heart Association): The problem that frequently occurred was that over time the blockage would re-accumulate so that the patient would often need another procedure within the next six months.

HAMILTON: Before long, though, doctors came up with what they thought was a perfect solution - stents. They're tubes made of wire mesh. Gibbons says doctors used angioplasty to widen arteries and then kept them open with stents.

Dr. GIBBONS: It turned out that they also had a problem over time of re-narrowing. They were less subject to that problem then balloon angioplasty, but it still occurred.

HAMILTON: That's because scar tissue would form around the stent. If there was too much scarring, it could close off an artery. Once again, doctors turned to technology for a solution. Companies began to make stents coated with drugs that would keep scar tissue from forming. The first model hit the market in 2003, and pretty soon coated stents dominated the field, even though they cost twice as much. Millions of people are now walking around with drug coated stents in their arteries.

Michael Domanski of the NIH says the stents have greatly reduced the number of patients who will need to have an artery reopened, but they've also created a new problem.

Dr. DOMANSKI: There may be a small increase in sudden clots, and that's a serious problem because it produces a heart attack and can produce death.

HAMILTON: No one knows for sure why the coated stents cause these blood clots, but doctors are once again looking for a solution. One clue comes from a study at Duke University. Researchers reviewed the medical records of hundreds of people there who got drug eluting stents at the medical center. All the patients took a drug called Plavix to reduce the chance that clots would form. That's standard practice. But patients who kept taking Plavix longer than six months were far less likely to die or have a heart attack.

David Kong, a cardiologist at Duke, says that suggests that long term use of Plavix could offset the risk of blood clots from coated stents.

Dr. DAVID KONG (Duke University): Certainly the previous recommendations that patients with drug eluting stents receive Plavix for either three or six months are likely insufficient given the data that we know now.

HAMILTON: Some doctors even think patients with the new stents should stay on Plavix for life. Tomorrow, FDA advisors will discuss how to care for patients who've got the new stents. There will be lots of talk about Plavix. But of course there's a new problem to solve. Plavix itself carries a small risk of bleeding.

Jon Hamilton, NPR News.

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