THURSDAY, Sept. 23 (HealthDay News) -- For people whose carotid arteries have become narrowed, restricting blood flow to the brain, having a surgical procedure to widen them reduces the risk of stroke over a 10-year period, British researchers report.

The carotid artery -- one on either side of the neck -- supplies blood carrying oxygen to the head, so a procedure to widen it helps restore blood flow to the brain. However, the operation, called a carotid endarterectomy, has about a 3 percent risk of causing an immediate stroke, the researchers cautioned.

For some elderly patients, this risk may outweigh any long-term benefit. But older, healthy patients will likely benefit from the procedure, the study authors noted.

However, Dr. Larry B. Goldstein, professor of neurology and director of the Duke Stroke Center at Duke University Medical Center, who was not involved in the study, suggested that the benefits might be smaller than they appeared in the study.

"Recent studies suggest that the rate of stroke in patients with [narrowed carotid arteries without symptoms] is lower than the rates found in this trial," he said. Although the study found the rate of stroke in patients without a carotid endarterectomy to be 1.8 percent a year over a 10-year period, Goldstein noted that "the rates are thought to be about 1 percent a year, but may be as low as around 0.5 percent a year."

The lower rates of stroke, he said, "are thought to be due to advances in medical treatment such as blood pressure control, antiplatelet drugs and more widespread use of statins."

The report is published in the Sept. 25 issue of The Lancet.

In the Asymptomatic Carotid Surgery Trial, a research team led by Dr. Alison Halliday of the John Radcliffe Hospital, the University of Oxford, randomly assigned 3,120 patients with narrowed carotid arteries to surgery or to no surgery until their condition required it.

Some of the patients originally assigned to the "no surgery" group did undergo the operation during the study, the researchers noted.

A total of 1,979 operations were performed. Among these the risk of stroke within 30 days was 3 percent, including 26 minor and 34 disabling or fatal strokes, Halliday's team reported.

Over an average of five years of follow-up, 4.1 percent of those who underwent the procedure suffered a stroke, compared with 10 percent of those who did not have the operation.

At 10 years, 10.8 percent of those who had the operation had suffered a stroke, compared with 16.9 percent of those who were not operated on, the researchers found.

The study authors noted that both groups included patients receiving blood pressure-lowering and anti-clotting drugs.

In addition, over the years of the study, patients in both groups were also taking cholesterol-lowering drugs. Even these medications did not affect the benefit of the surgery, the researchers said.

The benefit of the operation was seen for people who had the surgery before they were 75, but not among patients older than that, Halliday's group found.

"This trial took more than 15 years to complete, because we wanted to know about the long-term effects of surgery," Halliday said in a statement.

"The finding that successful carotid artery surgery can substantially reduce the stroke risk for many years is remarkable, because it means that most of the risk of stroke over the next five years in patients with a narrowed carotid artery is caused by that single carotid lesion. The definite benefits that we have found will be of practical value to doctors and patients deciding in the future whether to take the immediate risk of having such surgery," she said.

Overall, the study found benefit of endarterectomy in selected patients, Goldstein said.

The rates of stroke were reduced from about 2.2 percent a year to 1.4 percent a year over five years and from 1.8 percent a year to 1.3 percent a year over 10 years, he said.

"Decisions regarding whether or not to perform the operation must consider the overall small, but significant, benefit found in the study, the possibility that the benefit may be further reduced with modern medical therapy, individual patient characteristics, the surgeons' experience and complication rates, and patient preferences," he added.

This modest reduction in risk and the number of patients needed to treat to prevent one stroke may not be enough to justify performing the surgery on most patients, Goldstein said.

"This means that 24 operations would need to be performed to prevent one stroke over five years, or 22 operations to prevent one stroke over 10 years. This includes a 3 percent risk [of stroke from] the operation," he said, adding that there was no reduction in total mortality.

In a comment published with the study, Pierre Amarenco of Bichat Hospital in Paris, France, and colleagues wrote: "... it should be investigated further why the net benefit is not significant in patients older than 75 years, to distinguish whether some older patients could still benefit. Until then, decision making for these patients can only be on the basis of medical judgment for individual patients with in-depth discussions with the patient."

More information

For more information on stroke, visit the U.S. National Library of Medicine.