This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Subclan aery steal is caused by stenosis of the subclan aery at: 
Select and explain. 
A. Proximal to the takeoff of the veebral aery, B. Distal to the takeoff of the veebral aery, C. Middle pa, D. None of the above
A: Proximal to the takeoff of the veebral aery
Answer: A: Proximal to the takeoff of the veebral aery 
Explanation: Subclan aery steal is caused by stenosis of the subclan aery proximal to the takeoff of the veebral aery. This causes a retrograde flow in the ipsilateral internal mammary aery and the veebral aeries. Symptoms of subclan aery steal may include veigo and syncope with left arm exeion, angina, or ulcerated or gangrenous fingers. Blood pressures measured in the upper extremities are nearly always unequal. The average difference is a 45-mm Hg decrease in systolic pressure in the arm supplied by the stenotic vessel. Ref: Stone C., Strecker-McGraw M., Juergens A. (2011). Chapter 18. Syncope. In R.L. Humphries, C. Stone (Eds), CURRENT Diagnosis & Treatment Emergency Medicine, 7e.