Surveillance study participants were also less likely to have had any symptoms of stroke at the time of their stent procedure.

“There’s a reasonable explanation for that,” said Dr. William Gray, a cardiologist at Columbia University Medical Center and New York-Presbyterian Hospital, who has conducted post-market studies of stents. He was not involved in this study.

Gray said it all comes down to insurance; Medicare, in particular.

Medicare, the federally-funded health insurance for people over age 65, pays for stenting when people have symptoms.

When people don’t have stroke symptoms, they are more likely to enroll in studies - such as post-marketing surveillance - that will cover the costs of the procedure, Gray told Reuters Health.

Yeh agreed that insurance could partially explain the differences, but he thinks it doesn’t explain them all.

The risk of dying 2 years after stenting was also 20 percent lower among patients in the post-marketing studies than among people in the larger registry who didn’t enroll in a study.

Yeh said that difference might be explained by the skills of the physicians performing the stenting procedures for post-marketing studies.

“Maybe physicians are paying more attention,” Yeh told Reuters Health.

Or, it could be that studies exclude sicker patients, because people need to be well enough to sign and read papers and consent to joining the study, Yeh said.

The authors write that post-marketing surveillance studies “may be insufficient for monitoring long-term, community-based outcomes,” and that nationwide registries might be better able to fill that role.

The study, published in the journal Circulation, was funded by the American College of Cardiology Foundation, which developed the national database, or registry, of carotid artery stent procedures.

The Food and Drug Administration and Boston Scientific - a company that makes carotid artery stents - did not respond to requests for comment.

Another stent maker, Abbott, said in an email to Reuters Health, “the company is supportive of clinical registries as they contribute to the overall body of data on product use and provide additional data that help physicians treat their patients,” but would not comment on the study.

When the carotid artery becomes clogged, another option for widening it is to have surgery to remove the plaque. Doctors have debated the benefits of carotid artery stents versus surgery.

Neither procedure is ideal. People who have surgery are more likely to later have a heart attack, while those who undergo stenting are more likely to suffer a stroke later on (see Reuters report, October 11, 2010).

SOURCE: Circulation, online March 21, 2011.