Researchers make headway in probe of heart-stent clots


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 in the event an artery abruptly closed 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 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 David Marks, an associate professor of medicine at the Medical College of Wisconsin and director of the cardiac catheterization laboratory at Froedtert Hospital in Wauwatosa, Wis.

“They are speculating from very compelling and well-done data,” Marks said.

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 now 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.

The $6 million study funded by the National Institutes of Health will use heart catheterization films and blood samples from heart patients. About 1,200 patients from the Milwaukee area are expected to be enrolled in the study.

“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.

Because the field of collateral blood-vessel formation is so poorly understood, no one suspected the results from the new study, said Morton Kern, a professor of medicine at the University of California, Irvine. “It is one other potential downside to drug-eluting stents,” Kern said.

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, he 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 superior to bare-metal stents in preventing the gradual re-blockage of arteries, a troubling but seldom fatal process known as restenosis.

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 of those devices 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 in the appropriate setting. Compared with bare-metal stents, the drug-coated devices can substantially 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 their effectiveness and safety.

Drug-coated stent use results in an estimated 2,160 excess deaths in the U.S. each year, according to an October editorial in an online journal of the American College of Cardiology.

“Surely, it is time to refine the use of this innovative technology so that its benefits outweigh its cost and potential for harm,” said the editorial written by two California doctors.

At the University of Wisconsin Hospital in Madison, doctors already have become much more cautious in their use of drug-coated stents because of the recent reports of clots forming in the devices, said Giorgio Gimelli, director of the hospital’s cardiac catheterization laboratory.

Doctors had been using drug-coated stents about 90 percent of the time, but that has dropped to about 75 percent in recent months, he said.

“This has given us cold feet a little bit,” said Gimelli, an assistant professor of medicine. “We’ve changed practice fairly significantly.”

The new study on how drug-coated stents may affect collateral blood vessel formation adds another reason to be cautious, he said.

“We’d prefer not to see it, but it’s there and we’ll have to deal with it,” he said.