Carotid artery stenosis: External validity of the North American symptomatic carotid endarterectomy trial measurement method

PURPOSE: To assess the generalizability of the North American Symptomatic Carotid Endarterectomy Trial method for determining the degree of stenosis on angiograms. MATERIALS AND METHODS: Six good-quality, baseline angiograms of carotid arteries that were less than 70% stenosed were reviewed by 14 experienced neuroradiologists at different academic institutions. All reviewers determined the degree of stenosis by calculating the ratio of the diameter of the artery at the point of maximal narrowing to the normal diameter distal to the stenosis (well beyond the carotid artery bulb). The reviewers marked the location of their measurements on the angiogram. Comparisons were performed among the reviewers' results and with the reference measurements. RESULTS: Interobserver agreement was 0.84 (95% confidence interval = 0.65, 0.97). The average interobserver disagreement of +/-7% was comparable with that reported in the literature. The overall bias was 6%, which indicated a tendency of the reviewers to overestimate the degree of stenosis in comparison with the reference determination CONCLUSION: The North American Symptomatic Carotid Endarterectomy Trial reference measurements can be generalized beyond the bounds of this clinical trial, provided that attention is paid to details of the measurement method.