Subclavian steal phenomenon. Clinical and hemodynamic aspects.

Fifty-eight patients with subclavian artery stenosis were classified as having definite or probable vertebrobasilar symptoms, carotid symptoms or no symptoms. The vertebral artery flow pattern was graded as no subclavian steal (Grade 0), systolic deceleration (Grade 1), alternating flow (Grade 2), or reversed flow (Grade 3). We found a statistically significant association between the occurrence of vertebrobasilar symptoms and the subclavian steal phenomenon Grades 2-3. No significant association could be established between time course, type or severity of symptoms and grade of steal phenomenon. The flow disturbance is probably one causal factor for the occurrence of symptoms. Reversed vertebral artery flow is commonly asymptomatic, however, and other non-identified cofactors must be operative in symptomatic patients.