Opening the skull for a surgical procedure aimed at bypassing a blocked artery that supplies blood to the brain did not yield expected results. It did not lower the subsequent stroke rate after 2 years in people who previously had a minor stroke, compared to those who did not have the surgery.
The federally sponsored Carotid Artery Occlusion Surgery Study (COSS) was led by Dr. William Powers, distinguished professor and chair of neurology at the University of North Carolina at Chapel Hill. This clinical trial was designed to determine whether the subsequent stroke rate could be reduced if a branch of an artery in the scalp was used to bypass a completely blocked major neck artery, thereby increasing blood flow to the brain downstream.
The study enrolled patients at 49 medical centers in the U.S. and Canada. All had complete blockages of the internal carotid artery along with cerebral hemodynamic ischemia (insufficient blood flow to the brain). All also experienced a transient ischemic attack (TIA), a brief neurological dysfunction often called a "mini-stroke," or minor stroke in which blood supply to a part of the brain is temporarily reduced or stopped.
Of 195 patients, 97 were randomized to receive extracranial-intracranial (EI-IC) bypass surgery and medical treatment (anti-clot medication and risk factor intervention) and 98 patients were randomly assigned to medical treatment alone.
According to a report in the Nov. 9, 2011 issue of the Journal of the American Medical Association
), the study was "terminated early due to futility."
At the first follow-up 30 to 35 days following randomization into the study, 14 of 97 in the EI-IC surgery group (almost 15 percent) had another stroke, compared to only 2 of 98 (2 percent) in the nonsurgical group. At the end of 2 years, patients in the surgery group, compared with those who received medical therapy alone, did not have a reduced risk of recurrent stroke on the same side of the brain: 20 total patients in each group had a stroke.
Powers, also the senior author of the study, notes that the patients who made it through that first month without a stroke actually had their risk of subsequent stroke almost cut by three-fourths.
"With the advances of endovascular or catheter related techniques that have been developed to place stents in the carotid artery, it may be possible to open up blocked blood vessels with a much, much lower stroke risk than the bypass surgery.
"And so this study has really proven to us is if you can get more blood flow to that side of the brain in very high-risk people, you can really reduce their risk of having another stroke. The trick now is to figure out how to do that with a procedure that doesn't carry such a high risk of stroke itself that it negates the benefit. And that's the real question: whether or not these catheter-related procedures will be effective at doing that."
The UNC neurologist also notes that one of the most important aspects about the study can be found in the group of people with a completely blocked carotid artery. "Some of these people do very well on medical therapy - aspirin, statins, blood pressure control - and some of them don't," Powers said. "And one of the real values of the study is that it has confirmed our ability to identify that group of people who do not do well on medical therapy. It's the ability to identify this group that gives us the impetus to find a way to help them."