Subclavian steal: a harmless haemodynamic phenomenon?

500 patients with asymptomatic neck bruits were followed prospectively for up to 4 years with periodical standardised clinical assessments and continuous-wave carotid doppler ultrasonography, a reliable method for detecting subclavian steal. 9% of patients (45/500) had severe subclavian stenosis, and 64% of these (32/45) had a positive subclavian-steal test, with a preponderance of left-sided lesions (27/32). No patients had symptoms as a result of arm exercise during the steal test, and no patients had stroke during follow-up. Although reversed flow down one vertebral artery is relatively common in patients with generalised extracranial atherosclerosis, it is usually asymptomatic or causes, at most, vertebrobasilar transient ischaemic attacks.