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COSS: Ipsilateral ischemic stroke not reduced through extracranial-intracranial bypass surgery

Issue: December 2011

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Extracranial-intracranial bypass surgery plus medical therapy did not reduce the risk for recurrent ipsilateral ischemic stroke compared with medical therapy alone in participants with recently symptomatic atherosclerotic internal carotid artery occlusion, according to study results.

From 2002 to 2010, 195 participants with atherosclerotic internal carotid artery occlusion causing hemispheric symptoms and hemodynamic cerebral ischemia were enrolled in the Carotid Occlusion Surgery Study (COSS) and randomly assigned to a surgical group (n=97) or a nonsurgical group (n=98). The study showed no participants withdrew because of adverse events, and follow-up was 99% complete for primary endpoint until occurrence, 2 years or termination of trial.

There was a difference of 12.4% (95% CI, 4.9-19.9) for 30-day rates of ipsilateral ischemic stroke — 14.4% in the surgical group and 2% in the nonsurgical group — and a difference of 1.7% (95% CI, –10.4 to 13.8) for 2-year rates of primary endpoint of ipsilateral ischemic stroke, with the surgical group at 21% (95% CI, 12.8-29.2; 20 events) vs. 22.7% (95% CI, 13.9-31.6; 20 events) for the nonsurgical group. On-treatment analyses for primary endpoint at 2 years were 20.8% (95% CI, 12.4-29.1) for the surgical group vs. 22.3% (95% CI, 13.3-31.2) for the nonsurgical group. Assuming the original design effect size for the study was true, researchers found “a 29% chance of demonstrating a statically significant benefit for surgery if taken into completion.” Because of this analysis, the study was terminated for futility.

In an accompanying editorial, Joseph P. Broderick, MD, of the University of Cincinnati College of Medicine, and Philip M. Meyers, MD, of Columbia University, wrote: “[COSS] joins the list of stroke trials in which a successful outcome as measured by an important biologic marker of brain perfusion — improved oxygen extraction ratio after the bypass procedure — was not reflected in improved clinical outcome at 2 years. The pretrial assumptions regarding the 30-day postoperative stroke rate and the 2-year stroke rate in the surgical group were fairly accurate, but the 2-year stroke rate in the medical group was much lower than expected, possibly reflecting improvements in medical prevention of stroke during the conduct of the trial.”

For more information:

• Broderick, JP. JAMA 2011;306:2026-2027.
• Powers WJ. JAMA 2011;306:1983-1992.

Disclosure: Dr. Derdeyn reports receiving personal compensation as a consultant to W. L. Gore and Associates. Dr. Broderick reports receiving consulting fees from Genentech and as a member of the data and safety monitoring board for the NEST III trial. Dr. Meyers reports being the external interventional safety monitor for the IMS III trial.

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