Study design for randomized prospective trial of carotid endarterectomy for asymptomatic atherosclerosis. The Asymptomatic Carotid Atherosclerosis Study Group.

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Abstract
This report summarizes the study design and organization of a multicenter, randomized trial of carotid endarterectomy for the treatment of asymptomatic carotid stenosis. The Asymptomatic Carotid Atherosclerosis Study will determine whether the addition of carotid endarterectomy to aspirin plus risk factor modifications affects the incidence of ipsilateral transient ischemic attack, amaurosis fugax, and retinal and cerebral infarction in patients with asymptomatic hemodynamically significant carotid stenosis in at least one artery. Power calculations are based on assumptions of alpha = 0.05 (two-sided test) with annual event rate 3% transient ischemic attack and 1% cerebral infarction per year. The study has 90% power for detection of a 25% difference in events in a 5-year study. Two continuous validation programs are in use: a Doppler/angiogram correlation study for each Doppler instrument used in screening potential candidates and a transient ischemic attack/stroke questionnaire/validation study for verification of end points. Quality assurance is a major component in study design.