Drugs may make stents deadly, study says

MILWAUKEE — After months of alarm over the small but potentially fatal risk of blood clots forming in the coronary arteries of people who have been implanted with drug-coated stents, researchers say they may have discovered why the tiny devices can become deadly.

Drug-coated stents may hinder the heart's natural ability to form tiny collateral blood vessels that can salvage heart muscle by rerouting the blood supply, according to a new study.

This little-understood process, which is known as nature's bypass system, seems to be stunted by the medicine that coats the stents, but not by bare-metal stents, according to Swiss researchers whose study will be published Tuesday in the Journal of the American College of Cardiology.

In a study of 120 patients, there was 30 percent to 40 percent less collateral blood-vessel function in those implanted with the drug-coated stents, compared with bare-metal stents, six months after implantation.

The researchers theorized that this deficit could result in more serious damage to the heart should an artery abruptly close, such as when a clot occurs.

"Our results show that drug-eluting [coated] stents may hamper the heart's ability to salvage its own muscles," senior author Dr. Christian Seiler, a professor and physician at University Hospital in Bern, Switzerland, said in a statement. "... This could lead to a more severe heart attack."

The study presents some "very intriguing evidence," said Dr. David Marks, an associate professor of medicine at the Medical College of Wisconsin. "They are speculating from very compelling and well-done data."

Marks said the study provides more reason for doctors to make sure they have selected the correct stent for patients with coronary artery disease.

Medical College researchers are in the midst of their own five-year study to try to find genes linked to the heart's ability to grow new blood vessels when blockages occur.

"Some patients develop very vigorous collaterals," Marks said. "Other patients don't."

The difference may explain why some people survive heart attacks and why others die. The hope is that if a gene or genes are discovered, drugs that aid the process of collateral blood-vessel formation may be developed.

Because the field of collateral blood-vessel formation is so poorly understood, no one suspected the results from the new study, said Dr. Morton Kern, a professor of medicine at the University of California, Irvine.

The study likely will focus more attention on the process of collateral blood-vessel formation as well as developing new generations of drug-coated stents that don't hinder that process, Kern said.

When drug-coated stents became popular in 2003, they were heralded as a major breakthrough in treating heart disease. The tiny, expandable mesh-like tubes were shown to be far better than bare-metal stents in preventing the gradual re-blockage of arteries, a troubling but seldom fatal process known as re-stenosis.

Drug-coated stents are covered by medicine that slowly dissolves and that can dramatically reduce the formation of scar tissue that can re-block an artery. About 1 million Americans are implanted with stents each year, and an estimated 80 percent are drug-coated.

However, in recent months researchers and regulators have amassed evidence that in a small number of patients, drug-coated stents were associated with the formation of potentially deadly blood clots up to two years later.

Studies suggest that clot formation, a process known as thrombosis, occurs in 0.6 percent to 2.6 percent of patients who get drug-coated stents. Thrombosis is more common when a patient discontinues taking blood-thinning drugs.

Doctors say that even with the recent alarms about drug-coated stents, the devices still are worth the risk when used appropriately. Compared with bare-metal stents, the drug-coated devices can lower the risk of an artery re-narrowing with scar tissue.

At the same time, criticism has been leveled at some cardiologists for being too quick to use the devices, especially in so-called off-label circumstances where the devices are implanted for conditions in which clinical trials have not proven effective or safe.