Asymptomatic Embolization Detected by Doppler Ultrasound Predicts Stroke Risk in Symptomatic Carotid Artery Stenosis

Background and Purpose— Asymptomatic cerebral emboli can be detected using transcranial Doppler ultrasound (TCD). These embolic signals have potential as a marker of stroke risk and as a surrogate marker to evaluate antiplatelet agents. Small studies have demonstrated that they predict the combined endpoint of stroke and transient ischemic attack (TIA), but no studies have shown that they predict the more important endpoint of stroke alone. Methods— TCD was used to record for 1 hour from the ipsilateral middle cerebral artery in 200 patients with >50% symptomatic carotid stenosis. The Doppler audio signal was recorded for later analysis blinded to clinical details. Subjects were followed-up prospectively until surgical intervention, stroke, or study end at 90 days. Results— Embolic signals (ES) were detected in 89 (44.5%). During follow-up, 31 subjects experienced recurrent ipsilateral ischemic events: 7 strokes and 24 TIAs. The presence of ES predicted stroke alone (P=0.001) and the combined endpoint of stroke and TIA (P=0.00001). This remained significant, with an odds ratio of 4.67 (95% CI, 1.99 to 11.01; P<0.0001) after Cox regression to control for age, sex, smoking, hypertension, time from last symptoms, and degree of stenosis. The absence of ES identified a group at low risk for stroke alone and stroke and TIA during follow-up: 0% and 7.5%, respectively, versus 3.5% and 15.5% in all 200 subjects. Conclusions— Asymptomatic embolization in carotid stenosis predicts short-term ipsilateral stroke risk. This supports use of the technique to identify patients at high-risk for recurrent stroke for therapeutic interventions and as a surrogate marker to evaluate antithrombotic medication.