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Major Trial Confirms Benefit of Stroke Prevention Surgery

For release: Friday, September 30, 1994

Officials at the National Institute of Neurological Disorders and Stroke (NINDS) announced that surgery can prevent stroke in carefully selected individuals who have no outward sign of disease but are at risk for stroke from a severe narrowing of a major artery in the neck. The NINDS brought to an early conclusion a 7-year clinical trial investigating the effectiveness of a surgical procedure, called carotid endarterectomy, in reducing stroke in these individuals.

The trial, called the Asymptomatic Carotid Atherosclerosis Study (ACAS), found that surgery to remove fatty deposits from one of the main arteries in the neck supplying blood to the brain lowered the 5-year risk of stroke by about one-half, from greater than 1 in 10 to less than 1 in 20.

"This finding will be of vital interest for individuals who are at risk of stroke and who may already know that their carotid arteries are partially blocked," said NINDS Director Zach W. Hall, Ph.D. "During the last 48 hours the NINDS has taken steps to inform the medical community of these important results so that they might be better able to evaluate and advise patients on the risks and benefits of surgical treatment to prevent stroke."

As part of the $20 million trial, investigators at 39 sites in the United States and Canada studied 1662 men and women between the ages of 40 and 79 years with a 60 percent or greater narrowing of the carotid artery but no stroke-like symptoms attributable to the blockage. The study was carried out under the direction of James F. Toole, M.D., Director of The Stroke Center and Professor of Neurology at the Bowman Gray School of Medicine, Wake Forest University in Winston-Salem, North Carolina. The University of North Carolina School of Public Health at Chapel Hill served as the coordinating center on the study. In 1992, about 91,000 Americans had a carotid endarterectomy. Clinical trials in both North America and Europe have established that this surgery is highly beneficial for people who have had a stroke or stroke-like symptoms and a demonstrated blockage of 70 percent or more. However, the trials have left open questions as to the effectiveness of surgery in patients with less severe blockage as well as those with blockage and no symptoms of an impending stroke.

In this multi-center trial, investigators provided all patients with the best available medical care, including one adult aspirin daily and aggressive management of modifiable risk factors, such as counselling to help them stop smoking and treatment for high blood pressure, high cholesterol, and diabetes when indicated. Among the individuals in the study, 64 percent had high blood pressure, 26 percent had a history of cigarette smoking, 23 percent had diabetes, 21 percent had a previous heart attack, and 25 percent had a previous mild stroke or TIA unrelated to the carotid artery involved in the study.

In addition to best medical care, 828 randomly chosen patients also underwent surgery by a neurosurgeon or vascular surgeon who had demonstrated a complication rate of less than 3 percent for symptom-free patients based on an audit of their last 50 consecutive carotid endarterectomies.

"When surgery is performed to the standards set in this study, its long-term benefits clearly outweigh any short-term risks," said Michael D. Walker, M.D., director of the NINDS Division of Stroke and Trauma which oversaw the trial. "Appropriate use of this technique has the potential for preventing many thousands of strokes every year."

Dr. Toole and his colleagues showed that the surgical groups had a substantially lower risk of stroke (4.8 percent over a 5-year period) as compared with those who were managed medically (10.6 percent). Surgery conferred a relative risk reduction of 55 percent. Men in the surgical group had a 69 percent relative risk reduction, and women had a 16 percent relative risk reduction. According to the investigators, the reasons for this difference are unknown and will require additional study.

Scientists involved with this study point to the standards that were set to measure the blockage and caution against unfounded mass screening efforts. In order to be eligible for this study, patients had to have a 60 percent or greater blockage as determined by ultrasound and, in some cases, more extensive tests, and confirmed by arteriogram prior to surgery.

"This study highlights the fact that ultrasound alone may not be sufficient to select patients who can maximally benefit from carotid endarterectomy unless it is done in carefully calibrated ultrasound laboratories and confirmed by more extensive tests prior to surgery," said Dr. Walker.

Last Modified August 7, 2009