William M. Feinberg Award for Excellence in Clinical Stroke

Five percent to 15% of patients with carotid territory transient ischemic attacks or cerebral infarctions have complete occlusion of the internal carotid artery. Their risk of recurrent stroke during the next 2 years while on medical therapy is 5% to 9% per year for all stroke and 2% to 8% per year for ipsilateral ischemic stroke. Debate on the best means to prevent recurrence has centered on whether embolic or hemodynamic mechanisms are most important. In the late 1970s and early 1980s, embolism of atherothrombotic material from the persisting proximal stump of the occluded internal carotid artery through external carotid artery collaterals was put forward as the most common cause for recurrent cerebral ischemic events. At this same time, extracranial– intracranial (EC-IC) bypass was increasingly used to prevent recurrent stroke by improving the hemodynamic status of the cerebral circulation distal to the occluded vessel. From 1977 to 1985, an international, multicenter, randomized trial was conducted to determine the efficacy of EC-IC bypass for the prevention of subsequent stroke. Among 808 randomized patients with symptomatic carotid occlusion, no benefit of surgery was demonstrated. Some concluded that the reason for the negative results was that the majority of strokes were because of emboli, whereas others criticized the trial for failing to identify patients with hemodynamic cerebral ischemia because of poor collateral circulation for whom surgical revascularization would be of benefit. However, the pattern of arteriographic collaterals failed to identify a subgroup who benefitted from surgery. At the time of the EC-IC Bypass Study, there was no reliable method for assessing the hemodynamic effects of carotid artery occlusion on cerebral circulation. Although direct measurements of arterial-jugular venous oxygen differences had demonstrated that reductions in whole-brain cerebral blood flow (CBF) by induced systemic hypotension led to an increase in cerebral oxygen extraction fraction (OEF), jugular sampling was not useful for assessing the hemodynamic effects of unilateral carotid occlusion.