Doctors may soon be turning back the clock for some patients with complete atherosclerotic blockage of the carotid arteries, blood vessels in the neck that are important sources of blood for the brain.
Surgeons once regularly treated such blockages with a procedure known as a carotid bypass, which reroutes a scalp artery to restore normal brain blood flow and pressure. In the 1980s, doctors stopped using the procedure after a large study showed it did not appear to significantly improve patient outcomes.
Motivated by recent evidence suggesting that a subgroup of patients at higher risk of stroke might benefit from the bypass, physicians at Washington University School of Medicine in St. Louis and Barnes-Jewish Hospital are leading a multicenter trial to see if the surgery’s risks are offset by reduction in stroke risk. The study is seeking patient volunteers.
“When a complete blockage is identified in a patient’s carotid, many medical professionals think there’s nothing to be done for it,” says Colin Derdeyn, M.D., associate professor of radiology, neurological surgery and neurology. “We’d like to get the word out that there may be another option.”
Volunteers for the study will be screened to see if they belong to the high-risk group that may benefit from the bypass. Those who qualify will be randomly assigned to the bypass or to conventional treatment, which consists of prescribing daily doses of aspirin and regular follow-up examinations.
The renewed interest in the old operation stems from a study published in 1998 by Derdeyn and colleagues including William J. Powers, M.D., the Charlotte and Paul Hagemann Professor of Neurology and professor of neurosurgery; and Robert L. Grubb Jr., M.D., the Herbert Lourie Professor of Neurological Surgery and professor of radiation sciences. In that study, scientists found that connecting vessels from other arteries can compensate for blockage in the carotid artery, opening wider to keep brain blood flow close to normal levels.
However, in about half of the patients studied, these natural bypasses were not enough to keep brain blood flow normal. In these patients a second compensatory process became active: their brains increased the amount of oxygen they took from the blood.”
Under normal circumstances, brain tissue only takes about 30 percent of oxygen provided to it by the blood stream. As blood flow decreases, that rate, known as the oxygen extraction factor (OEF), can increase to as high as 80 percent. Scientists measure OEF with PET (positron emission tomography) scans.
In the 1998 study, researchers showed that high OEF in patients with carotid occlusions was a “powerful” predictor of stroke risk. Patients with increased OEF had an extremely high risk for stroke, while those with normal OEF had a very low risk.
By restoring normal blood flow and bringing down OEF, the carotid bypass may be able to reduce high stroke risk dramatically enough to make the procedure worthwhile for some patients with carotid blockage. The current multicenter study, the Carotid Occlusion Study (COSS), will determine if surgical complications from the bypass are low enough to justify recommending the procedure for all patients with occluded carotids and high OEF.
Epidemiologists estimate that there are 750,000 strokes in the United States annually. Many of these involve complete blockage of a carotid artery, according to Derdeyn.
“Everyone who has a stroke should be screened for carotid occlusion because half of patients with occlusions will have high OEF and an extremely high risk of future stroke,” Derdeyn says. “The results of COSS will provide critical information regarding the best way to treat these people and reduce their stroke risk.”
For more information or to volunteer for the study, call Mary Catanzaro, COSS research nurse coordinator, at (314) 362-3466.
Washington University School of Medicine’s full-time and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked third in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.
Funding from the National Institutes of Health supports this research.