Effect of subclavian syndrome on the basilar artery.
Fifty-five patients with a permanent or intermittent subclavian steal syndrome demonstrated by continuous wave Doppler were included in a prospective study: 25 patients without vertebro-basilar symptoms, 8 symptomatic patients with defined vertebro-basilar symptoms and 22 with hemodynamic vertebro-basilar occurrences. The basilar artery velocity was recorded by Transcranial Doppler Sonography in baseline conditions, and after a hyperaemia test to the upper limb. A spontaneous, incomplete basilar steal was diagnosed in seven patients, and a complete basilar steal in one patient, (14.5% of the cases). After hyperaemia test, 18 other incomplete basilar steal were observed. The occurrence of a basilar steal was higher in the vertebro-basilar group (57% of the cases) especially in 7 of the 8 cases with defined vertebro-basilar symptoms; it was lower in the patients without vertebro-basilar occurrences (36% of the cases). This basilar steal was also seen in five of the six symptomatic patients with opposite vertebral artery stenosis above a 50% diameter. Transcranial Doppler Sonography could help to define a subgroup of subclavian steal syndrome with a high risk of strokes.