Subclavian Steal Syndrome - Signs and Symptoms

Introduction

A pair of subclavian arteries are situated below the collar bones in the neck as the left subclavian artery and right subclavian artery. The two arteries have different origins. The right subclavian artery originates from the brachiocephalic trunk and the left subclavian artery originates directly from the aortic arch. Despite different origins, the arteries follow the same course along the neck region. The function of each subclavian artery is to receive the oxygenated blood from the heart and supply it to other parts of the body such as to the thyroid, neck region, chest, brain, and upper limbs. The normal diameter of the subclavian artery is 0.7 to 1 centimeter.

What Is Subclavian Steal Syndrome?

Subclavian steal syndrome (SSS) is otherwise known as subclavian-vertebral artery syndrome. When there is a narrowing or blocking of the subclavian artery located proximal to the origin of the vertebral artery, the blood flows backward in the vertebral artery present on the same side as the subclavian artery.

What Is the Etiology of Subclavian Steal Syndrome?

The most common etiological factor is the condition of fat and cholesterol buildup on the inner walls of the arteries called atherosclerosis. The frequency of subclavian steal syndrome occurring on the left subclavian artery is more due to its more acute and sharp origin of the artery. It causes more atherosclerosis due to increased turbulence. Males are more prone to this syndrome than females. There are some risk factors associated with the syndrome listed below.

• Compression of the Subclavian Artery: The subclavian artery compression in its course present in the space between the collar bone and first rib (thoracic outlet) can be a risk factor for the syndrome. This neuromuscular compression in the thoracic outlet is common among cricket bowlers and baseball players.

• Right Aortic Arch: Congenital heart conditions like the right aortic arch where the aortic arch is present on the right side instead of the left side is a potential risk factor.

• Takayasu Arteritis: The inflammation of large blood vessels due to infiltration by granulomatous tissue is called Takayasu arteritis. It is more prevalent in young and middle-aged women.

• Cervical Rib Syndrome: It is the presence of an extra rib that arises from the seventh cervical vertebrae.

• Coarctation of Aorta Repair Surgery: Post-surgical treatment of coarctation of the aorta that is narrowing of the aorta can also be a risk factor.

• Anatomical Factors: Rare anatomical abnormalities are also risk factors. These include aortic dissection, congenital malformation of the vertebral artery, and compression of the vertebral artery.

• Other common secondary factors are advancing age, diabetes, high blood pressure, high cholesterol, smoking, and a family history of cardiac disease.

How Does Subclavian Steal Syndrome Occur?

The physiology behind the symptoms caused due to subclavian steal syndrome is the diversion of blood flow from the brain to the arm. The symptoms caused are similar to vertebrobasilar insufficiency (reduced blood flow to the back portion of the brain). The symptoms arise especially during intense arm exercises and sudden sharp turning of the head to the direction of the affected side. There are two mechanisms by which the arm steals or gets blood diverted from the brain area:

• By reduced blood supply due to stenosis or narrowing of the subclavian artery.

• By an abnormal connection between an artery and venous plexus in the distal part of the arm.

What Are the Stages of Subclavian Steal Syndrome?

Based on the severity of the disease, there are three categories or grades of the syndrome.

• Grade Ⅰ: It is a pre-subclavian steal stage. It is a reduction in the forward or antegrade flow of blood in the vertebral artery.

• Grade Ⅱ: It is a partial or intermittent stage. There is alternate forward flow in the diastolic phase and backward flow of blood in the systolic phase of the cardiac cycle.

• Grade Ⅲ: It is a more severe and advanced stage where the retrograde or backward blood flow is permanent.

How Is Subclavian Steal Syndrome Examined?

The syndrome is asymptomatic in most patients. The following findings during the routine physical examination can be suggestive of this syndrome.

• The blood pressure difference of at least 15 mmHg between the normal and the affected arm can help diagnose the disease.

• Ultrasound of arteries done during coronary artery or carotid artery disease will reveal the condition.

• On palpation of the radial pulses of both arms simultaneously, the affected arm shows delayed arrival and decreased amplitude.

• Simultaneous palpation and auscultation of right and left carotid arteries can detect the disease.

What Are the Signs and Symptoms of Subclavian Steal Syndrome?

The symptoms can be mild or severe. They are as follows:

• Pain, numbness, and fatigue in the arm.

• Tingling sensation in the affected arm.

• Weakness in the affected arm.

• Difficulty in speaking is called aphasia.

• Difficulty in motor skills and coordination is called ataxia.

• Headache and dizziness.

• Fainting.

• Vertigo and light-headedness.

• Visual disturbances like blurring of vision.

• Tinnitus or ringing sound in the ear.

• Loss of hearing.

How Is Subclavian Steal Syndrome Diagnosed?

1. Duplex Ultrasound: It is the first choice of investigation done at the bedside. It is less invasive and can even detect a borderline case of subclavian artery stenosis. If the systolic velocity of the subclavian artery peaks at 240 cm per second, it suggests severe subclavian artery stenosis.

2. Magnetic Resonance Angiography: It is an accurate diagnostic test. It can examine both intracranial and extracranial blood circulation of arteries.

3. Computed Tomography Angiography: This diagnostic test is done after abnormal findings on duplex ultrasound. It helps in the grading of arterial stenosis.

4. Digital Subtraction Angiography (DSA): This test is taken after the treatment has been decided. If stenting has been chosen as the treatment, it can reveal the anatomical challenges of the surgery.

What Is the Treatment of Subclavian Steal Syndrome?

Asymptomatic patients require no treatment and the health status of patients with mild symptoms improve with time.

1. Lifestyle Changes: Control and prevention of risk factors can prevent the development of stenosis such as control of blood sugar and blood pressure, discontinuation of smoking habit, reduction of cholesterol levels in the blood, and maintaining a healthy lifestyle.

2. Surgery: For symptomatic patients, open bypass surgery is the surgical option. Extra-anatomic revascularization is the choice of bypass surgery where a bypass is created using non-anatomic structures from the outside.

3. Endovascular Intervention: It is an innovative and less invasive procedure with minimal postoperative risks, indicated in borderline patients where a mesh stent is placed to prevent stenosis in the subclavian artery. Balloon angioplasty is another option.

4. Anticoagulation Therapy: In patients with high surgical risks and where the patient’s arterial anatomy is unfavorable for surgery, antiplatelet therapy is advised. Blood is prevented from getting clot due to stenosis. But its efficacy in preventing the disease is unknown.

Conclusion

The syndrome is a relatively mild abnormality. But it is a significant risk marker for atherosclerosis and other fatal diseases (like heart attack and stroke) that follow. Patients with severe disease have a good prognosis after surgical intervention. There are no serious complications from the syndrome.