Which of the following statement is true regarding subclan steal syndrome

Subclan steal syndrome may occur if it is the first pa of the subclan aery that is obstructed, with the veebral aery providing a collateral circulation into the arm by reversing its direction of flow. It is associated with neck pathology like cervical rib.This may cause periods of cerebral ischaemia. However, the classic syndrome of syncopal attack and visual disturbance associated with arm exercise and a diminished blood pressure in the affected limb is rare,asymptomatic reversal of flow in the veebral aery is much more common. In symptomatic patients, PTA or operation is indicated. Reference:Bailey & Love's sho practise of surgery,25th edition,page no:909