The first method uses transcranial Doppler (TCD) to count the number of presumed embolic events, known as high-intensity transient signals per unit time. Although this technique has shown that patients with frequent high-intensity transient signals have a higher subsequent stroke rate than those without high-intensity transient signals, the test Meschia et al Guidelines for the Primary Prevention of Stroke 3783 is time-consuming to perform and has not received uniform acceptance. Additionally, the effect of intensive medical ther- apy on high-intensity transient signals has not been adequately assessed. Another method of study uses plaque analysis in a computerized algorithm using B-mode insonation of the carotid plaque. Population screening for asymptomatic carotid artery stenosis is not recommended by the US Preventive Services Task Force, which found no direct evidence that screening adults with duplex ultrasonography for asymptomatic stenosis Screening for other risk factors is addressed in relevant sections of this guideline. Asymptomatic Carotid Stenosis: Summary and Gaps Medical therapy has advanced since clinical trials have been completed comparing endarterectomy plus best medical ther- apy with best medical therapy alone in patients with an asymp- tomatic carotid artery stenosis.541 Recent studies suggest that the annual rate of stroke in medically treated patients with an asymptomatic carotid artery stenosis has fallen to 1%.541 543 In the ACST, the rate of absolute benefit from CEA per year was lower in patients on lipid-lowering therapy (0.6%/y) compared with patients not on lipid lowering therapy (1.5%/y).544 ACST had no explicit targets for LDL, and intensive targets (eg, LDL <70 mg/dL) may further reduce the benefit of revascularization. Statin therapy is appropriate for patients with asymptomatic carotid stenosis, whether or not they undergo revascularization. Interventional therapy has also advanced, particularly in terms of perioperative management and device design. 