Surgical procedures aimed at bypassing blocked arteries that supply blood to the brain do not lower the subsequent stroke rate after two years in people who previously had a minor stroke, according to a new study.

Researchers at the University of North Carolina (UNC; Chapel Hill, USA) and 48 other clinical centers and 18 positron emission tomography (PET) centers in the United States and Canada conducted the parallel-group, randomized, Carotid Artery Occlusion Surgery Study (COSS) clinical treatment trial from 2002 to 2010 to test the hypothesis that extracranial-intracranial (EC-IC) bypass surgery, added to best medical therapy, reduces subsequent ischemic stroke in patients with symptomatic atherosclerotic internal carotid artery occlusion (AICAO) who had recently experienced a transient ischemic attack (TIA). Of the 195 patients, 97 were randomized to receive surgery and 98 to no surgery; antithrombotic therapy and risk factor intervention were recommended for all participants.

The study was terminated early for futility. Two-year follow-up rates for the primary end point--a combination of all stroke and death from surgery through 30 days after surgery and ipsilateral ischemic stroke within 2 years of randomization--were 21% for the surgical group and 22.7% for the nonsurgical group, a difference of 1.7%. Thirty-day rates for ipsilateral ischemic stroke were 14.4% in the surgical group and 2% in the nonsurgical group, a difference of 12.4%. The study was published in the November 9, 2011, issue of the Journal of the American Medical Association (JAMA).

“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,” said lead author professor of neurology William Powers, MD. “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 purpose of EC-IC bypass is to augment cerebral blood flow. This procedure entails connection of the superficial temporal artery (STA), or a venous conduit, to a branch of the middle cerebral artery (MCA). EC-IC bypass has been available as a potential treatment for stroke for the past 30 years; during this time, the procedure and its indications have undergone intense scrutiny and reevaluation as a legitimate therapy, engendering controversy among neurosurgeons and neurologists. The procedure has been touted as a great technical achievement, and at other times a therapeutic failure.

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