Carotid Subclavian Bypass

Abstract

Carotid subclavian bypass historically was a procedure primarily performed in the management of subclavian stenosis or occlusion. The main indication for carotid subclavian bypass was vertebral basilar insufficiency (posterior cerebral circulation) related to reduced perfusion to or retrograde flow (subclavian steal syndrome) in the ipsilateral vertebral artery. The common carotid artery serves as the donor artery with normal pulsatile perfusion reestablished to the distal subclavian artery and thereby the vertebral artery. One important additional indication for carotid subclavian bypass is the anatomic situation in which the left internal mammary graft has been used (or is going to be used) for the graft for coronary artery bypass in the presence of subclavian artery occlusive disease. The carotid subclavian bypass functions to maintain perfusion to the left internal mammary artery (LIMA) supplying the coronary circulation. More recently, with the introduction of endovascular repair of thoracic aortic aneurysms, the primary indication has been with debranching procedures in which the subclavian orifice, due to the need to secure a proximal landing zone, is covered by the proximal extent of the thoracic endovascular aneurysm repair (TEVAR) graft. Carotid subclavian bypass is typically performed a few days prior to the TEVAR but can be performed concomitantly if necessary. In instances in which upper extremity ischemic symptoms develop post urgent or emergent TEVAR, bypass is also warranted. Absolute indications for this bypass when TEVAR coverage of the left subclavian is anticipated are: (1) absent right vertebral; (2) small or diseased right vertebral; (3) left vertebral which terminates in the posterior inferior cerebellar artery; and (4) history of prior LIMA coronary graft. Carotid subclavian bypass is notable for an excellent patency profile. The operation is performed through a single supraclavicular incision and consists of exposure of the common carotid artery in the medial aspect, exposure of the subclavian artery deep to the anterior scalene in the mid-aspect of the wound, and a tunnel created posterior to the internal jugular vein. Important structures which need to be identified and preserved from injury include the vagus nerve (during exposure of the common carotid), the phrenic nerve (during the subclavian artery exposure), and the thoracic duct (empties into the subclavian vein near the confluence of the left internal jugular and the left subclavian vein). The operation is well tolerated through a single relatively small incision—however, the proximity of important structures including the vagus nerve, phrenic nerve, brachial plexus, venous structures, and the thoracic duct renders this an operation in which one must be vigilant to avoid excessive traction or injury that can result in nerve palsies or chyle leaks.