Subclavian Steal Syndrome

The upper limb is supplied primarily via the axillary artery, the continuation of the subclavian artery that exits the thoracic outlet. On the right, the common carotid artery and the subclavian artery share a common trunk, commonly known, perplexingly, as the innominate (ie, nameless) artery but also referred to as the brachiocephalic artery or trunk.

In some congenital anomalies, the right subclavian artery may arise directly from the aorta as the last supra-aortic trunk (known as an aberrant right subclavian artery), or it may be isolated. On the left, the subclavian artery typically arises directly from the aorta as the last supra-aortic trunk.

Described branches from the subclavian arteries from proximal to distal include the vertebral arteries, the internal mammary artery (IMA; also known as the internal thoracic artery), the thyrocervical trunk, and the costocervical trunk before it becomes the axillary artery.

In the setting of severe proximal subclavian artery stenosis or occlusion, typically due to atherosclerotic disease, insufficient flow may be present to sustain the ipsilateral arm. In this case, the branches of the subclavian artery may be recruited to provide collateral retrograde flow to the upper limb. For example, the IMA provides anastomoses to the superior epigastric and intercostal arteries. The thoracoacromial trunk anastomoses with vessels in the neck and thoracic wall.

Of greatest relevance for present purposes are the confluence of the vertebral arteries at the basilar artery and its subsequent communication with the circle of Willis, which allow the ipsilateral vertebral artery to provide flow in a retrograde manner (see the image below) from the contralateral vertebral artery or from the anterior cerebral circulation.

Retrograde blood flow from left vertebral artery into left subclavian artery in patient with subclavian steal syndrome.

With exercise, innate and metabolite-induced vasodilatation leads to a drop in peripheral resistance in upper-limb vessels, and the mismatch between arterial inflow and metabolic demand may lead to claudication of the arm. Furthermore, increased retrograde flow through the ipsilateral vertebral artery may “steal” blood away from the cerebral circulation. This may be more likely if there is concomitant stenotic disease of the other extracranial or intracranial vessels.

In these patients, neurologic symptoms consistent with cerebral or brainstem ischemia may develop. In a 1991 study of 43 patients undergoing carotid duplex study who were incidentally found to have retrograde vertebral artery flow, 16% had posterior circulation symptoms (dizziness, vertigo, blurred vision, diplopia, and near-syncope) upon exercise of the ipsilateral arm; 30% had similar symptoms that were present even at rest; 21% had anterior circulation hemispheric symptoms referable to a carotid territory; and 33% were asymptomatic at all times.[3]

With the increasing use of the left IMA (LIMA) as a conduit for coronary artery bypass grafting (CABG), a phenomenon often referred to as coronary subclavian steal has become recognised. Where proximal subclavian artery disease develops or progresses in the setting of previous LIMA graft coronary bypass, the LIMA graft may become reliant upon the retrograde vertebral flow. Exercise of the upper limb may result in diversion of flow from the LIMA graft into the arm, resulting in myocardial ischemia or angina.

The underlying factor leading to subclavian steal is proximal subclavian artery occlusion or severe stenosis. In most cases, this is a result of atherosclerotic arterial disease, which has a preponderance for the left side. On the right side, innominate artery disease or occlusion may result in occlusion of the subclavian artery origin.

The risk factors for developing atherosclerotic plaques have been recognized for some time and are categorized as either nonmodifiable or modifiable. Nonmodifiable risk factors include the following:

• Age
• Male sex
• Family history

Modifiable risk factors include the following:

• Cigarette smoking
• Hypercholesterolemia
• Diabetes mellitus
• Hypertension
• Hyperhomocysteinemia

Although retrograde blood flow in the vertebral artery is usually noted angiographically in association with proximal ipsilateral subclavian artery occlusion, subclavian steal may also occur with hemodynamically significant subclavian artery stenosis (see the image below).

Irregular proximal subclavian stenosis.

Other, less common causes of subclavian occlusive disease include inflammatory arteriopathies such as Takayasu arteritis or giant cell arteritis. Congenital anomalies may also result in isolation of the subclavian artery and sacrifice of the proximal subclavian artery in aortic surgery (eg, a Blalock-Taussig procedure for tetralogy of Fallot or coverage of the left subclavian origin with a thoracic endovascular stent graft).

Thoracic outlet compression syndrome can cause subclavian artery occlusion, but this typically involves the subclavian artery beyond the vertebral artery origin.

Although peripheral arterial disease affects about 20-25% of Americans older than 70 years, the vessels of the upper extremity are affected much less often than those of the lower extremity are. Because most patients do not seek medical advice unless symptoms occur, the true prevalence of subclavian artery occlusive disease and subclavian steal syndrome is unknown.[4]

The left subclavian artery is the aortic arch branch vessel most commonly affected by atherosclerosis; therefore, it is not surprising that the left subclavian artery is involved with subclavian steal three times more frequently than the right subclavian artery is.

In the Joint Study of Extracranial Arterial Occlusion, Fields and Lemak found that 17% of the 6534 patients admitted to the study had arteriographic evidence of subclavian or innominate stenosis greater than 30% or occlusion[5] ; however, only 168 patients had symptoms of subclavian steal syndrome. Berguer et al found that only half of their patients with significant subclavian occlusive lesions manifested reversal of blood flow in the ipsilateral vertebral artery.[6]

Patients with asymptomatic flow reversal in a vertebral artery have a benign natural history, and no specific treatment is required.

With proximal subclavian artery occlusive disease, patients may first seek medical treatment for symptoms of exercise-induced arm claudication rather than for neurologic symptoms associated with arm exercise. Furthermore, if a patient has undergone coronary revascularization with a LIMA graft, new-onset angina may herald proximal left subclavian stenosis. With subclavian steal syndrome, if neurologic symptoms do occur, they tend to be transient (eg, hypoperfusive transient ischemic attack) and seldom lead to stroke.

For patients in whom antegrade vertebral blood flow is reestablished by means of either surgical revascularization or endovascular stenting of the diseased subclavian artery, the prognosis is highly favorable. The stroke risk from the procedure is low, and the long-term durability is excellent.

Operative morbidity and mortality are substantially higher for transthoracic subclavian artery revascularization than for extrathoracic repair, mainly because of the morbidity associated with thoracotomy. Recognizing this problem, surgeons have virtually abandoned this approach in favor of extrathoracic revascularization in the form of either carotid-subclavian bypass or subclavian transposition. Operative mortality for either of these extrathoracic procedures approaches zero, and morbidity is very low.

The results of retrograde (brachial puncture) or antegrade (femoral puncture) percutaneous subclavian angioplasty or stent placement are also excellent.[7] Most authors report initial success rates of 91-100%, and the complication rate is reasonably low (3-17%). After successful stenting of the subclavian artery, the restenosis rate is 0-16% after 12-48 months’ follow-up. The technical success rate of subclavian angioplasty ranges from 86% to 100%. The restenosis rate after subclavian angioplasty is 5-22% after 28-60 months’ follow-up.

Patients with retrograde blood flow in a vertebral artery are usually asymptomatic. In addition, with few exceptions, proximal subclavian stenosis or occlusion rarely causes symptoms of arm ischemia. Muscle cramping due to arm ischemia typically occurs in laborers performing vigorous work, often with arms elevated above the head. If the increased oxygen demand from arm exercise exceeds the ability of collateral vessels to provide sufficient blood flow, cerebral ischemia may occur as more blood is siphoned from the brain via the vertebrobasilar system.

Numerous symptoms are associated with posterior-circulation cerebral ischemia. Symptoms of dizziness or vertigo occur in more than 50% of patients, and syncope and dysarthria have been noted in 18% and 12.5%, respectively. Visual symptoms secondary to vestibular dysfunction or nystagmus include a sensation of objects moving and inability to focus, as well as monocular or binocular visual loss. Diplopia occurs in 19% of cases. Fortunately, these transient ischemic episodes seldom progress to cause cerebral infarction.

True subclavian steal syndrome cannot occur without retrograde blood flow in a vertebral artery associated with proximal ipsilateral subclavian artery stenosis or occlusion. In a healthy individual, blood pressures in both arms should be similar. Without a significant difference in blood pressure between the patient’s arms, proximal subclavian stenosis or occlusion cannot be present.

An invariable finding in patients with symptoms of subclavian steal syndrome is a difference in upper-extremity pulses and brachial systolic blood pressures between the patient’s arms. Therefore, with a simple physical examination, the clinician can effectively eliminate significant subclavian arterial lesions without the need for angiography or duplex ultrasonography (US).

The internal mammary artery (IMA) arises from the inferior aspect of the proximal subclavian artery, opposing the origin of the vertebral artery. Recurrent symptoms of angina pectoris after otherwise successful coronary revascularization with a left IMA (LIMA) graft may also indicate a hemodynamically significant proximal left subclavian stenosis.

Atherosclerotic lesions (stenosis or occlusion) of the proximal vertebral artery may produce similar symptoms. Occlusive disease of the vertebral artery should be considered if posterior circulation symptoms occur with normal blood pressures in the affected arm.

After an adequate physical examination, routine laboratory studies should be ordered to address risk factors for atherosclerosis. These tests should include a fasting lipid profile and blood glucose.

Imaging studies that may be considered include duplex ultrasonography (US), computed tomography (CT) angiography (CTA), four-vessel cerebral arteriography, magnetic resonance angiography (MRA), and chest radiography.[8] (See Subclavian Steal Syndrome Imaging.) Electrocardiography (ECG) may also be considered.

Duplex US is the most important test of the extracranial carotid and vertebral arteries, as well as the subclavian artery. It can demonstrate retrograde blood flow in the vertebral artery and any significant occlusive lesions of the carotid arteries in the neck.

Subclavian steal syndrome is now most commonly diagnosed during Doppler US examination of the neck arteries.[9] In most cases, because of anatomic constraints imposed by the chest wall, it is difficult to assess the proximal subclavian artery adequately by means of US.

Searching for significant lesions in the ipsilateral carotid artery is important. If brachial artery pressures are significantly decreased (>20%) in comparison with the contralateral side, arch aortography should be performed to further define the problem and plan for operative or interventional repair.

Although conventional angiography remains the gold standard investigation for the diagnosis of subclavian occlusive disease in most centers, CTA has replaced this modality as the first-line test. It has a high sensitivity and specificity and has the advantage of being able to identify other lesions in the arch vessels. No arterial puncture is required. Currently, CTA is regarded as excellent for planning and sizing in endovascular treatment, and only rarely is conventional four-vessel arteriography required.

Four-vessel cerebral arteriography can define the problem anatomically, demonstrating retrograde blood flow in the vertebral artery and associated proximal occlusive subclavian artery lesions. In addition, arteriography serves as a road map for possible repair (surgical or endovascular) of the subclavian artery.

MRA has become an alternative to conventional angiography for the assessment of subclavian steal syndrome, especially in patients with renal dysfunction. Unfortunately, however, MRA often overestimates the degree of arterial obstruction and is associated with a higher degree of false-positive results.

Chest radiography is performed to look for unusual causes of subclavian artery obstruction (eg, cervical rib).

Because many of these patients have concomitant ischemic heart disease, ECG is advisable.

Patients with atherosclerotic occlusive plaques in the subclavian artery are usually asymptomatic and therefore require no treatment. However, if either vertebrobasilar symptoms or exercise-induced arm pain occurs, a search for subclavian artery occlusive disease should be undertaken.

No medical therapy is known to be capable of effectively treating subclavian steal syndrome. However, if the cause of subclavian steal syndrome is determined to be atherosclerotic stenosis or occlusion of the proximal subclavian artery, patients should be treated with lifelong antiplatelet therapy to reduce the risk of associated myocardial infarction, stroke, and other vascular causes of death.

If the ischemic symptoms are due to retrograde vertebral artery blood flow, surgical or interventional (ie, angioplasty or stenting) therapy is indicated. The goal is to restore antegrade blood flow in the vertebral artery, thereby alleviating symptoms. This goal can be achieved by restoring adequate perfusion pressure to the affected arm so that collateral blood flow from the head and neck is not required during arm exercise. At present, it is unclear whether stenting is more effective than angioplasty alone for stenosis of the subclavian artery.[2]

Surgical or interventional treatment should not be offered to treat subclavian artery stenosis or occlusion in the absence of symptoms related to either cerebral or ipsilateral arm ischemia. Symptoms (eg, ataxia, dysarthria, diplopia, and muscle cramping in the arm) must be associated with exercise and resolve quickly after cessation of exercise.

First described in 1962 by DeBakey, the transthoracic approach to endarterectomy provided an excellent anatomic view for revascularizing the subclavian artery. Currently, direct surgical approaches to the proximal subclavian artery are of historical interest only, because endarterectomy has largely been replaced by less invasive extrathoracic bypass procedures; intraoperative mortality had ranged from 6% to 19%.

With endarterectomy, the artery is opened after vascular control is obtained, and the plaque, diseased intima, and internal elastic lamina of the vessel are removed, thus disobliterating the lumen.

Because the occlusive lesions in the proximal left subclavian artery develop as an extension of plaque from the aortic arch, partial occlusion of the arch must be performed to ensure that the entire lesion is effectively removed. On the left side, surgical exposure must be obtained through an anterolateral thoracotomy in the third intercostal space. On the right side, exposure can be accomplished through a transverse incision in the base of the neck without the need for thoracotomy.

In patients with severe concomitant carotid artery disease, this condition may contribute to cerebral hypoperfusion in the setting of subclavian steal. Carotid endarterectomy for carotid bifurcation disease may improve cerebral perfusion. Proximal common carotid artery disease may be best approached angiographically for angioplasty or stenting.

Extrathoracic carotid-subclavian bypass

Extrathoracic carotid-subclavian bypass using a prosthetic conduit has largely replaced subclavian endarterectomy; mortality is 0.5%. Surgical exposure is easily obtained through a transverse incision at the base of the neck that extends 5-7 cm laterally from the sternal notch parallel to the clavicle.

Conventionally, 6- to 8-mm Dacron or polytetrafluoroethylene (PTFE) prosthetic grafts are used; autogenous vein has poor 5-year patency rates.[10] End-to-side (graft-to-artery) anastomoses can be performed without difficulty. The procedure is generally well tolerated.

Subclavian transposition

The subclavian artery can also be transposed to a new origin on the side of the common carotid artery. This operation is also performed through a transverse incision at the base of the neck and has the advantages of not requiring prosthetic material and of excluding the stenosis as a source of potential emboli. The dissection required is more extensive than that required for carotid-subclavian bypass, and care must be taken to avoid injury to the thoracic duct on the left side. An end-to-side subclavian-to-carotid anastomosis is performed.

Long-term results are similar to those of carotid-subclavian bypass. In patients who have an early origin of the vertebral artery or have had an internal thoracic artery harvested for coronary surgery, the bypass procedure is preferred.

Axillary-axillary bypass and variants

In settings where the ipsilateral carotid is unsuitable for carotid-subclavian bypass, the axillary artery may be revascularized via axillary-axillary bypass using a subcutaneously tunneled ring-reinforced prosthetic graft. Alternatively, axillofemoral bypass may be performed. These grafts are often superficial and are prone to infection. In severe innominate artery disease, antetracheal or sequential retroesophageal carotid-carotid and carotid-subclavian bypass can be performed.

Operative details

Before surgical bypass or transposition, arch aortography must be performed to ensure that the proximal common carotid and distal subclavian arteries are relatively free of disease. During aortography, it is important also to visualize the carotid and vertebral arteries because these vessels often contain other hemodynamically significant lesions that can contribute to the symptoms of subclavian steal syndrome.

For either carotid-subclavian bypass or subclavian transposition, an incision is made approximately 2 cm cephalad to the clavicle, extending laterally through the attachments of the clavicular head of the sternocleidomastoid. The scalene fat pad is identified, and care is taken to preserve the phrenic nerve that traverses from lateral to medial across the anterior aspect of the scalenus anticus. The muscle is divided, exposing the subclavian artery. The common carotid artery is easily exposed through the medial aspect of the same incision.

On the left side, the thoracic duct must be avoided. This structure is visualized near its junction with the proximal internal jugular vein. After systemic heparinization, control of the carotid and subclavian arteries is achieved, and a bypass is performed with a 6- to 8-mm PTFE or Dacron prosthetic graft. End-to-side anastomoses are performed to the common carotid and subclavian arteries.

Subclavian transposition requires more proximal dissection of the subclavian artery to ensure that a sufficient length of the artery is available to allow the anastomosis to be performed without undue tension. Additional care must be undertaken to control the proximal stump of the subclavian artery; bleeding in the superior mediastinum is difficult to manage. A partially occluding clamp on the common carotid is not necessary.

Complete carotid occlusion with a proximal and distal clamp affords a better view of the intima, and the short period of ischemia is generally well tolerated. Shunting of the common carotid artery during occlusion is usually unnecessarys but may be warranted if there is disease of the contralateral common or internal carotid arteries. Drains may also be placed during closure.

In the early postoperative phase, patients should be monitored for neurologic deficit. Head elevation helps reduce swelling in the surgical incision. Brachial blood pressures are taken in both arms and are expected to be remarkably similar after the procedure.

Currently, endovascular (ie, catheter-based) treatment of the proximal subclavian artery is the most common approach to the management of proximal subclavian lesions. Although open bypass or transposition is the gold standard, retrospective analysis shows that in appropriately selected patients, endovascular treatment has equally good outcomes. A study comparing early and long-term outcomes of endovascular repair with those of open surgical repair in patients with subclavian artery atherosclerotic occlusive disease found the two approaches to be comparably safe, effective, and durable.[11]

The technical success rate is 86-100%. In comparison with the open technique, complications with the endovascular technique are associated more with plaque emboli and bleeding from access sites than with local nerve injury. Moreover, most of these endovascular procedures can be performed successfully on an outpatient basis.

Although to date, there have been no double-blind randomized, controlled trials comparing balloon angioplasty alone with angioplasty and stenting for this condition, a systemic review of multiple retrospective observational studies concluded that stenting was superior to balloon angioplasty alone.[12]

Endovascular recanalization and stenting improve perfusion to the arm and treat subclavian steal syndrome (see the image below). Because plaque in the proximal subclavian artery is actually part of the atherosclerotic lesion in the aortic arch, the stent must traverse the entire plaque and protrude slightly into the lumen of the aortic arch.[13]

Successful stent treatment of subclavian stenosis, with restored antegrade flow into vertebral artery.

Procedural details

As with carotid-subclavian bypass or subclavian transposition, arch aortography should be performed before the procedure. This can be done via a right femoral access by using a multiple-sidehole catheter and a power injector.

As in any endovascular procedure, a guide wire must first be placed across the lesion. If the origin of the subclavian artery is not well defined, guide-wire placement may be more easily accomplished through the ipsilateral brachial artery or the radial artery in a retrograde direction.[14] On the other hand, if a stump of the patent proximal subclavian artery is visible, an antegrade approach via a right femoral artery access can be attempted.

Proper preparation of both access sites (brachial and femoral) is essential. If stenting is planned, the patient is given 5000 U of intravenous (IV) heparin. In general, balloon-expandable stents perform well in this location; they can be precisely placed and possess greater radial strength than self-expanding stents do. Care is taken to ensure that the subclavian stent does not compress the lumen of the ipsilateral vertebral artery or internal mammary artery. After stent placement, a selective subclavian arteriogram is obtained to confirm technical success.

After the procedure, patients should be monitored for 3-4 hours in a recovery area to confirm that no bleeding or hematoma has occurred in the access site. Neurologic status should also be monitored, and blood pressure should be recorded in both arms.

Surgical treatment

Complications related to surgical treatment may be classified as either local or cerebral. Local complications are related to injury to adjacent structures that may be encountered during the course of the operation (eg, the thoracic duct injury or the phrenic nerve) and are quite uncommon.

Cerebral complications are related to brain ischemic symptoms and can be caused either by thrombosis of the repair or by embolism up the carotid or vertebral arteries during the course of the procedure. Cerebral ischemia during common carotid occlusion is most unusual; therefore, a shunt is not used for the procedure. Postoperative stroke rates are in the range of 1.5-2.1%.

Endovascular treatment

Complications related to endovascular treatment can occur at the access site (femoral or brachial artery) or at the target vessel (subclavian or vertebral artery). Access site bleeding or hematoma is very uncommon but can occur. Target vessel thrombosis, dissection, or distal embolization have also been reported. These complications occur less than 4% of the time.

In a study comparing immediate and long-term results of endovascular treatment of steno-occlusive disease of subclavian arteries in 245 patients (125 with subclavian stenosis and 120 with subclavian occlusion), Karpenko et al reported intraoperative transitory ischemic attacks in the vertebrobasilar system in one patient from group 1 and three from group 2.[15] Nine patients from group 1 and 12 from group 2 had repeat interventions in the long term. Cumulative primary 4-year stent patency was 89.8% in group 1 and 87% in group 2. There was an increased risk of stent thrombosis or in-stent restenosis in patients with stents longer than 40 mm.

There are no standardized guidelines for follow-up after treatment. Patients are seen at 3- to 6-month intervals for the first year and annually thereafter. At every visit, blood pressures should be checked in both arms. A decline in pressure on the operated side may be the first sign that recurrent stenosis may be developing.

Follow-up duplex scans of the reconstruction should be obtained at 6-month and 1-year intervals. Patients who have had subclavian stents should be treated with both aspirin and clopidogrel for a period of 6-12 months. Thereafter, a single antiplatelet agent is appropriate.

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Class Summary

Antiplatelet agents inhibit platelet aggregation and reduce ischemic events. Patients should be treated with lifelong antiplatelet therapy to reduce the risk of associated myocardial infarction, stroke, and other vascular causes of death, if the cause of subclavian steal syndrome is determined to be atherosclerotic stenosis or occlusion of the proximal subclavian artery.

Aspirin (Bayer Aspirin, Ascriptin Maximum Strength, Ecotrin, Bufferin)

Aspirin inhibits prostaglandin synthesis, which prevents the formation of platelet-aggregating thromboxane A2.

Clopidogrel (Plavix)

Clopidogrel selectively inhibits adenosine diphosphate (ADP) binding to platelet receptors and subsequent ADP-mediated activation of the glycoprotein (GP) IIb/IIIa complex, thereby inhibiting platelet aggregation.

Ticlopidine

Ticlopidine hydrochloride interferes with platelet membrane function by inhibiting adenosine diphosphate (ADP)–induced platelet-fibrinogen binding and subsequent platelet-platelet interaction. It is used as a second-line antiplatelet therapy for patients who are intolerant of aspirin therapy or in whom such therapy fails.