Since its introduction 40 years ago, the value of
carotid endarterectomy has been controversial. In the early 1980s, several clinical trials were initiated to determine the efficacy of this operation in patients with
carotid stenoses who were either symptomatic or asymptomatic for
retinal or hemispheric
ischemia. In 1991, interim results were published for the North American Symptomatic
Carotid Endarterectomy Trial (NASCET) and the European Carotid Surgery Trial (ECST), both reporting efficacy for surgery in patients with symptomatic
carotid artery stenosis of greater than 70%. Subgroup analyses revealed variable risk groups. The Veterans Administration (VA) Symptomatic Trial (Cooperative Studies Program 309 of the Department of Veterans Affairs) terminated early because of these results and its findings were consistent with the results of the larger trials. NASCET and ECST continue for symptomatic patients with
carotid stenoses between 30% and 69%. The results of three trials in asymptomatic patients, the Mayo asymptomatic trial, the
Carotid Artery Stenosis with Asymptomatic Narrowing: Operation Versus
Aspirin trial, and the VA Asymptomatic Trial (Cooperative Studies Protocol 167 of the Department of Veterans Affairs), have been reported. None showed a statistically significant benefit for surgery in the prevention of
stroke or death. However, none was sufficiently large to exclude such a benefit. The large Asymptomatic
Carotid Atherosclerosis Study is in progress. Differences in the results and design of these trials are discussed as are restrictions in the applicability of their results.