Subclavian Steal Syndrome

Retrograde blood flow in the vertebral artery and proximal subclavian stenosis or occlusion may remain asymptomatic. Strenuous, physical work can aggravate arm ischemia resulting in muscle cramping, particularly when the work includes holding arms above the head. Cerebral ischemic symptoms ensues when more blood is siphoned off from the vertebrobasilar artery. Vertigo, ataxia and dizziness are the most common symptoms in patients with posterior circulation cerebral ischemia. Other symptoms include syncope and dysarthia. Vestibular dysfunction results in ocular and visual symptoms like aberrant focus, sensory disturbances, and visual loss.

On physical examination, significant difference exists in the blood pressure between the two arms. A difference of 10 mmHg in systolic pressure between the arms is strongly associated with subclavian stenosis [9]. Difference in the upper extremity pulses and brachial systolic blood pressure between the arms are indicative of SSS. A subclavian bruit is audible in some cases. Differential diagnosis includes aortic dissection, arteritis, atherosclerosis, multiple sclerosis, and brain tumor.

A thorough physical examination can reveal many of the signs of the syndrome. Laboratory studies including blood glucose and fasting lipid profile are used to assess the risk of atherosclerosis, one of the most important causes of stenosis. Imaging techniques like CT scan, angiography, MRI, four-vessel cerebral arteriography and ECG may be considered [10]. The most important among them is duplex ultrasonography that helps to trace carotid, vertebral and subclavian artery for presence of occlusion or stenosis. It is also useful in detecting retrograde blood flow in the vertebral artery. Doppler ultrasonography of neck arteries is ideal for diagnosing SSS [11]. Arch aortography is effective in defining and locating lesions in the carotid artery. This evaluation is helpful in defining features of occlusion, and also in assessing the need for surgical intervention.

Computed tomography angiography has high specificity and sensitivity in diagnosing stenosis and occlusive lesions in subclavian artery. Other lesions in the arch vessels can also be revealed by this procedure. But, four-vessel arteriography is more appropriate for endovascular treatments as diagnosis and treatment can be done simultaneously in the vessel. MRA is the mode of choice for diagnosis and assessment of SSS, particularly in patients with renal dysfunction. Chest radiography may be of help in cases with unusual causes of occlusion. And if ischemic heart disease is suspected, ECG is suggested.

Patients who are asymptomatic for occlusions in the subclavian artery may not require any special treatment. Occlusions should be located and assessed in case of cerebral ischemic or upper limb ischemia. There are no definite treatment modality for clearing SSS. If atherosclerosis is the etiological factor behind the occlusion or stenosis, antiplatelet therapy is suggested. This often has to be continued lifelong to reduce the risk of different vascular disorders including myocardial infarction and stroke. Surgery or interventional treatment is recommended in case of symptoms due to vertebrobasilar insufficiency. This helps to improve the symptoms by restoring blood flow in the arteries.

Proximal subclavian endarterectomy is a surgical procedure to remove the plaque along with the affected part of intima of the blood vessel. Care should be taken to remove the entire lesion including those from the aortic arch. If carotid artery disease is concomitant with SSS, cerebral hypoperfusion is common. Carotid endarterectomy is useful in these cases to improve the symptoms. Subclavian bypass is now preferred over endarterectomy as it is less invasive. Prosthetic conduit ensures a carotid-subclavian bypass. Transposition of the affected subclavian artery to the side of common carotid artery is also a preferred procedure with good long-term outcome. If bypass cannot be performed for the ipsilateral carotid, axillary-axillary bypass helps in revascularization.

Endovascular treatment of the occlusion also has a good prognosis with a success rate of 86%-100%. This procedure aids in improving perfusion of the arm and thus improve most of the symptoms associated with SSS. This minimally invasive procedure is the preferred method, particularly in high-risk patients.

Patients who are asymptomatic for retrograde blood flow may not require any specific treatment. Most of the neurologic symptoms of SSS remain transient as in hypoperfusive transient ischemic attack. Surgical intervention for revascularization or stenting of the affected artery provides a good prognosis. Morbidity and mortality is reported to be high for transthoracic subclavian artery revascularization when compared to carotid-subclavian bypass or transposition. Prognosis for subclavian angioplasty and stenting is favorable. Complication rate also remains low for the two procedures.

Occlusion and severe stenosis of the proximal subclavian artery is the most important factor leading to SSS. Atherosclerosis is the most common cause of steno-occlusive lesions, and is a major etiologic factor of SSS in 94% of the cases [3]. The structure of left subclavian artery, with a pronounced angle at the origin, accelerate the formation of atherosclerotic lesions. Incidence of occlusions and stenosis is in left artery in 80% cases of SSS. Occlusion of the right subclavian artery results from innominate artery disease. Incidence of right and bilateral artery symptoms are very rare [4]. Thus, risk factors of atherosclerosis are indirectly associated with increased risk of developing SSS. Other etiologic factors that increase the risk of this syndrome include trauma, arteritis, post-surgical intervention, congenital abnormalities, and thoracic outlet syndrome.

There is paucity of information on the worldwide prevalence of SSS. Some studies from different centers report the prevalence as ranging from 0.6% to 3.4% [4]. Difficulty in true estimation arises from the fact that most of the patients with retrograde blood flow remain asymptomatic. Occlusion and stenosis of the left subclavian artery is three times more commonly involved in the syndrome than the right artery. Incidence of the disease increases with age.

The incidence of the syndrome is more frequent among Caucasians, who are more susceptible to atherosclerosis. It is more prevalent among men with a male to female ration of 2:1. Frequency of occurrence is more among people above 55 years of age [5]. In the Far East, about 36% of the patients with SSS suffer from Takayasu arteritis. Here the age of presentation is lesser than 30 years and the male to female ratio is reverse with more affected females than males.

Stenosis of the proximal subclavian artery results in a lower pressure in the distal subclavian artery, creating a retrograde flow in the vertebral artery. The difference in pressure pulls the blood from the vertebral artery to the basilar and then down to ipsilateral vertebral artery. This results in a reduced flow in the cerebral circulation [6]. Retrograde flow may be continuous or intermittent, categorized as complete or incomplete [7]. With reduced perfusion to ipsilateral arm, symptomatology of the arm including paresthesis, weakness of the arm, and claudication, sets in [8]. Cerebral ischemic symptoms arise when the intracranial collateral circulation is inadequate. Presence of lesions in other parts of the intracranial or extracranial cerebral circulation also result in ischemic symptoms.

Controlling the risk factors of atherosclerosis is the best method of preventing SSS. This include quitting smoking, treating hypertension, dyslipidemia, and diabetes.

Subclavian steal syndrome (SSS) or subclavian steal phenomenon is a vascular phenomenon characterized by steno-occlusive lesions in the subclavian artery proximal to the origin of vertebral artery. The occluded subclavian artery then ‘steals’ the blood from vertebrobasilar artery leading to vertebrobasilar insufficiency. SSS is more prevalent in males and is generally found in people above the age of 55 years.

Subclavian steal syndrome often remains asymptomatic and may be found during an occasional test conducted for other indications. A difference of more than 20 mmHg in the blood pressure between the two arms is a valid clinical reason for suspecting SSS. Reduced blood flow may cause cerebral ischemic symptoms and/or symptoms of upper limb ischemia [1]. Recanalization, angioplasty and stenting, artery transposition, and carotid-subclavian bypass are some of the options for treatment. Any treatment modality aims at restoring antegrade vertebral artery blood flow, improving cerebral perfusion, and increasing arterial perfusion in the upper arm [2]. Management of risk factors like hypertension and diabetes are also equally important for the successful treatment of the condition.

Subclavian steal syndrome (SSS) is an uncommon form of vascular disorder characterized by a blockage in subclavian artery that results in symptoms involving arm and brain. The subclavian arteries provide blood to each arm and also to the base of the brain. SSS occurs when there is a partial or complete blockage in subclavian artery just before the branching of vertebral artery. When the arm supplied by the blocked artery is under stress, blood is pulled from brain through the vertebral artery. This often results in severe, cramp-like pain in the arm due to insufficient flow of blood to the arm. Blood is thus literally stolen from the brain to supply the arm, and hence the name ‘steal’ syndrome. It is more common among men when compared to women, and is usually seen in people above the age of 55 years.

Many patients with this syndrome remain asymptomatic and SSS is found incidentally during the diagnosis of other diseases or disorders. The most common sign of this syndrome is the difference in the blood pressure between the two arms. Vision problems, vertigo, numbness of arm, seizures, headaches, confusion and dizziness are also seen as symptoms. Atherosclerosis is the major cause for the blockage of subclavian artery. Any factor that increases the risk of atherosclerosis like smoking, high lipid content, and hypertension, increases the risk of this syndrome as well. Apart from a thorough physical examination, ultrasonography, angiogram, chest radiography, ECG and MRI are also used in locating and defining the presence of blocks in the arteries.

Symptoms often improve with medical therapy, particularly in cases where there are no specific symptoms. Angioplasty is suggested, if medical therapy is not effective in improving the symptoms. Surgery helps to bypass or transposition the affected artery. More popular treatment methods include recanalization and stenting of the blocked artery. This method is more popular as it is less invasive and can be done under a local anesthetic. Treatment is generally preserved for those having specific symptoms of the arm and brain.

1. Sharma VK, Chuah B, Teoh HL, Chan BP, Sinha AK, Robless PA. Chronic brainstem ischemia in subclavian steal syndrome. J Clin Neurosci. 2010;17(10):1339-1341. 
2. Henry M, Henry I, Klonaris C, Hugel M. Percutaneous transluminal angioplasty of the subclavian arteries. In: Henry M, Ohki T, Polydorou A, Strigaris K, Kiskinis D, editors. In Angioplasty and stenting of the carotid and supra-aortic trunks. London: Springer; 2004:655-656.
3. Langer DJ, Lefton DR, Ostergren L, et al. Hemispheric revascularization in the setting of carotid occlusion and subclavian steal: a diagnostic and management role for quantitative magnetic resonance angiography? Neurosurgery. 2006;58(3):528–33.
4. Labropoulos N, Nandivada P, Bekelis K. Prevalence and Impact of the Subclavian Steal Syndrome. Ann Surg. 2010;252:166.
5. Perler BA, Becker GJ. Vascular intervention: A clinical approach. London: Thieme; 1998. p. 474-5.
6. Williams CL, Scott SM, Takaro T. Subclavian steal. Circulation. 1936;28:14.
7. Berger R, Sidd J, Ramaswamy K. Retrograde Vertebral-Artery Flow Produced by Correction of Subclavian-Steal Syndrome. N Engl J Med. 1967;277:64–69.
8. Chan-Tack KM. Subclavian steal syndrome: a rare but important cause of syncope. South Med J. 2001;94(4):445–47.
9. Clark CE, Taylor RS, Shore AC, et al; Association of a difference in systolic blood pressure between arms with vascular disease and mortality: a systematic review and meta-analysis. Lancet. 2012;379(9819):905-914.
10. Potter BJ, Pinto DS. Subclavian steal syndrome. Circulation. 2014;129(22):2320-3.
11. Moghazy KM. Value of color Doppler sonography in the assessment of hemodialysis access dysfunction. Saudi J Kidney Dis Transpl. 2009;20(1):35-43.