The term "subclavian steal" refers to a phenomenon of flow reversal in the vertebral artery ipsilateral to a hemodynamically significant stenosis or occlusion of the subclavian artery [1,2]. In most cases, subclavian steal is asymptomatic, does not warrant invasive evaluation or treatment, and represents an appropriate physiological response to proximal arterial disease. Subclavian steal syndrome implies the presence of significant symptoms due to arterial insufficiency in the brain (ie, vertebrobasilar insufficiency) or upper extremity which are supplied by the subclavian artery.
The physiology, diagnosis, and treatment of subclavian steal will be reviewed here. General considerations for patients with symptoms of vertebrobasilar ischemia are discussed in detail elsewhere. (See "Posterior circulation cerebrovascular syndromes".)
Subclavian artery occlusion or a hemodynamically significant stenosis proximal to the origin of the vertebral artery results in lower pressure in the distal subclavian artery. As a result, blood flows from the contralateral vertebral artery to the basilar artery, and may flow in a retrograde direction down the ipsilateral vertebral artery, away from the brainstem (figure 1) [3-5]. Reversed vertebral artery flow, although it may have deleterious neurologic effects, serves as an important collateral artery for the arm in this setting.
Coronary-subclavian steal — A coronary-subclavian steal phenomenon has been described in patients who have undergone prior coronary artery bypass surgery (CABG) utilizing the internal mammary artery (IMA) [6,7]. In the presence of a hemodynamically significant subclavian artery stenosis proximal to the origin of the ipsilateral IMA, flow through the internal mammary artery may reverse and "steal" flow from the coronary circulation during upper extremity exercise (figure 2). Coronary and graft angiography demonstrate retrograde flow in the involved IMA during selective catheterization of the grafted coronary artery . Simultaneous coronary and cerebrovascular ischemia have also been reported [7,9]. Identification of a significant subclavian artery stenosis prior to CABG can prevent this important problem. Those patients with a high-grade subclavian artery stenosis should be treated (percutaneously or surgically) prior to CABG . (See 'Treatment' below.)
Atherosclerosis is the most common cause of subclavian steal syndrome which is more common on the left side, possibly due to a more acute origin of the left subclavian artery, resulting in accelerated atherosclerosis from increased turbulence .