The Asymptomatic Carotid Emboli Study: study design and baseline results

Background Better methods of identifying which patients with asymptomatic carotid stenosis will develop stroke, are required to improve the risk-benefit ratio of carotid endarterectomy. A promising method is the detection of asymptomatic embolic signals using transcranial Doppler. Embolic signals predict stroke risk in symptomatic carotid stenosis, but their predictive role in asymptomatic carotid stenosis is uncertain. Aims The Asymptomatic Carotid Emboli Study is a prospective observational study in patients with asymptomatic carotid stenosis ≥70%. Method Two 1-h transcranial Doppler recordings from the ipsilateral middle cerebral artery are performed at baseline, and a single-hour recording is performed at 6, 12 and 18 months. Follow-up is for 2 years. All recordings are centrally blinded to subject identity during analysis. The primary hypothesis is: do embolic signals on either of two 1-h recordings at entry predict ipsilateral transient ischaemic attack and stroke risk over the following 2 years? The major secondary hypothesis is: does the presence of embolic signals on a single-hour-long recording at baseline or at 6, 12 or 18 months predict ipsilateral transient ischaemic attack and stroke risk over the subsequent 6-month period? Results Recruitment was completed in October 2007 with 482 subjects. At the baseline, the proportion of subjects with embolicsignals was 10·7% on recording 1,10·8% on recording 2 and 16·7% on either of the two recordings. Embolic signal prevalence on the two recordings was significantly associated (χ2 27·48, P