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Carotid–Subclavian Bypass and Other Nonanatomic Revascularizations for Proximal Subclavian Artery Stenosis
In the past, subclavian revascularization was most often performed to relieve either vertebrobasilar symptoms or exertional arm pain associated with subclavian steal syndrome. Currently, subclavian revascularization is increasingly undertaken to extend the proximal landing zone during endovascular management of thoracic aortic conditions including aneurysm, dissection, and trauma. Additionally, subclavian revascularization may be appropriate to maintain or restore normal inflow to the mammary artery used in coronary artery bypass ( Figure 1 ).
Subclavian steal. Because of decreased pressure distal to subclavian artery stenosis or occlusion, blood flow may be reversed in the vertebral and internal mammary arteries to provide collateral circulation to the arm. Flow reversal may be present at all times or may be intermittent during arm exertion or neck movements that compress other cervical vessels.
Surgical correction of subclavian steal syndrome is recommended for patients with severe, repetitive symptoms that affect lifestyle, increase the risk of injury from falling, or threaten the ability of the patient to live independently. In addition, c arotid subclavian bypass is one of several techniques used to restore perfusion pressure to an internal mammary artery bypass used in a coronary artery revascularization. Bilateral brachial blood pressures should be checked in all patients before internal mammary bypass and reassessed if angina recurs at follow-up.
Emergence of endovascular treatment for a variety of thoracic aortic conditions has led to a significant increase in the need for subclavian revascularization to extend the proximal landing zone and preserve spinal cord blood supply ( Figure 2 ). While the role of subclavian revascularization continues to evolve, the Society for Vascular Surgery practice guidelines currently recommend routine preoperative subclavian revascularization in elective cases and in cases in which coverage of the subclavian artery would compromise perfusion of critical organs. In particular, subclavian revascularization is recommended in the settings of a dominant left vertebral artery, a left vertebral artery terminating in the posterior inferior cerebellar artery (PICA), or extensive coverage of the thoracic aorta, which could compromise spinal cord blood flow.
Subclavian revascularization may be required to extend the landing zone for thoracic endografting. A, Subclavian–carotid transposition. B, Carotid–subclavian bypass with synthetic graft
(Figure from Riesenman PJ, Farber MA, Mendes RR, et al: Coverage of the left subclavian artery during thoracic endovascular aortic repair, J Vasc Surg 45:90–95, 2007.)
Anatomy
The subclavian artery travels laterally between the anterior and middle scalene muscles. Three segments of the subclavian artery are defined by their relation to the anterior scalene muscle. The internal mammary artery, the vertebral artery, and the thyrocervical trunk arise from the first part of the subclavian artery medial to the anterior scalene muscle. The thyrocervical trunk gives rise to the inferior thyroid artery, the suprascapular artery, and the transverse cervical artery, which may be safely ligated if necessary. The costocervical trunk typically originates from the second part of the subclavian artery deep to the anterior scalene muscle and divides into the superior (supreme) intercostal artery and the deep cervical artery. The deep cervical artery can represent a significant ascending collateral vessel in the setting of ipsilateral vertebral occlusive disease. The third segment of the subclavian artery gives rise to the dorsal scapular artery, typically at the lateral border of the first rib, marking the distal boundary of the subclavian artery. Substantial variation in the branches of the subclavian artery are common and must be anticipated to avoid bothersome bleeding.
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