To analyze the effect of degree in subclavian artery steal (SAS) caused by vertebral artery stenosis (VAS).

Totally 148 patients with serious stenosis (70%-99%) of unilateral subclavian artery (SA) diagnosed by vascular ultrasonography during August 2013 to May 2015 were studied retrospectively. According to the degree of VAS, patients were classified as vertebral artery severe stenosis (VASS) group (53 cases) and non-VASS (degree of stenosis less than 70%) group (95 cases). The cases in VASS group were classified into two sub-groups: the patients (23 cases) with lesions of VA and SA ipsilateral and the patients (30 cases) with contralateral vertebral artery (VA) lesions. The degree of SAS were classified by the blood flow waveform examined by color dopplor flow imaging (CDFI) of intertransverse segment of the VA. The difference of the degree of SAS between the two major groups and sub-groups were compared and analyzed by χ² test.

The degree of SAS in patients with severe stenosis of unilateral SA were occult steal accounted for 50.9% (27/53), partial steal accounted for 47.2% (25/53) and complete steal accounted for only 1.9% (1/53) in VASS group; while in non-VASS group, partial steal accounted for 73.7% (70/95) and complete steal accounted for 26.3% (25/95). There were statistical significances of the degree of SAS between VASS group and non-VASS group (χ²=63.679, P=0.000). The degree of SAS of the two subgroups according to the ipsilateral or contralateral side of the lesion had no statistical significant difference (χ²=0.782, P=0.676). The blood flow spectrum of VA were mainly characterized as occult steal and the decrease of blood flow velocity and low resistance in the SAS patients with VASS.

The severe stenosis in vertebral artery might possibly lead to a decrease in SA steal. VASS is an important influential factor for the mismatching between the SA stenosis and SA steal.