FRIDAY, May 9 (HealthDay News) -- Stents have become a cornerstone of heart-disease treatment, tiny tools that have extended the lives of millions of patients by maintaining the flow of blood through their arteries.

The wire metal mesh tubes, when inserted following artery-clearing angioplasty procedures, can prop open the artery and ensure a constant supply of blood to the heart and throughout the body.

But stents aren't perfect. Scar tissue causes them to re-close in about one in five patients, requiring a follow-up procedure to remove and replace the stent, lest the patient suffers a heart attack, said Dr. Laura Mauri, an assistant professor of medicine at Harvard Medical School and Brigham and Women's Hospital, in Boston.

New stents that were approved by the U.S. Food and Drug Administration in 2003 are coated with a drug to prevent too much scar tissue from forming. But some research has shown that the drug can increase the risk of too little scar tissue forming and a blood clot appearing in the stent.

"If not enough scar tissue forms to cover the stent, the metal can create a blood clot on its own," said Dr. Jack Tu, a senior scientist at Canada's Institute for Clinical Evaluative Sciences and a professor with the University of Toronto. "It's a fine balance. You want some scar tissue to form around the stent, but you don't want too much to form."

As doctors and scientists continue to pursue ways to improve heart health, the debate over drug-coated stents versus bare-metal stents continues to simmer.

In the latest development, the U.S. Food and Drug Administration announced in December that it is preparing to issue new testing requirements for drug-coated stents. The revised rules, created in response to concerns about stent safety, are expected to be more stringent than current rules. They are expected to specify the numbers of patients on whom new drug-coated stents can be tested and for how long, and to offer a recommended length of time patients should take anti-clotting drugs after receiving a stent.

Stents are inserted by collapsing them to a small diameter and placing them over a balloon catheter, according to the American Heart Association. When the balloon is inflated in a blocked artery, the stent expands, locks in place and forms a scaffold that holds the artery open.

The stent stays in the artery permanently, keeping blood flowing and relieving symptoms like chest pain. Within a few weeks of the procedure, the inside lining of the artery grows over the metal surface of the stent.

For patients whose arteries are clogged with plaque, the procedure is a simple one that usually takes a few hours, according to the U.S. National Institutes of Health. They are awake during the procedure but under sedation, and generally the only sensation felt is when the balloon is expanded to push the stent into place.

Drug-coated stents are recommended particularly for patients with an increased risk of suffering from reclosure, Tu said. These patients include people with diabetes and people with smaller-than-normal blood vessels or long lesions left by their heart disease.

"Those are the patients who seem to derive the most benefit," Tu said.

The drug-coated stents have been quite successful in preventing the need for repeat procedures, Mauri said.

"The coated stents have medication on them," she said. "The medicine releases slowly over time and prevents cells from building up that could lead to a blockage."

Tu and Mauri have both conducted large studies showing that the drug-coated stents can be as safe as the bare metal ones that preceded them.

However, even proponents of drug-coated stents note that they have their risks, mainly involving the medications that must be taken with them.

To prevent a blood clot, patients with drug-coated stents must take a strict regimen of anti-clotting medications for at least one year following the procedure.

"Patents who are unable to comply with this regimen should be treated with bare-metal stent implantation," said Dr. Murtuza J. Ali, an interventional cardiology fellow at the Boston University Medical Center.

The patients who can't follow the anti-clotting drug regimen are mainly people who will have to receive bare-metal stents instead, Tu said. "If the person is going to need some sort of surgery over the next year, they may be better off receiving the bare-metal stent," he said.

If the patient isn't diligent about taking the anti-clotting drugs, a heart attack could result over time, Mauri said.

"We know if these medicines are stopped early, there are risks of blood clots forming inside the stent," she said.

More information

To learn more about stents, visit the American Heart Association.

SOURCES: Laura Mauri, M.D., assistant professor of medicine, Harvard Medical School and Brigham and Women's Hospital, Boston; Jack Tu, M.D., Ph.D., FRCPC, senior scientist, Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada, and professor of medicine, University of Toronto; Murtuza J. Ali, M.D., interventional cardiology fellow, Boston University Medical Center; American Heart Association; U.S. National Institutes of Health

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