What is Subclavian Steal Syndrome?
Subclavian steal syndrome (SSS), also known as subclavian-vertebral artery steal syndrome, is a condition that prompts a change in blood flow direction in an artery near your spine, caused by narrowing or blockage of the subclavian artery, which is close to the point where the spine-originating artery begins. Basically, it’s when the subclavian artery – which supplies the arm with blood – gets blocked, causing the blood to flow in the opposite direction to reach the arm.
In most cases, subclavian steal syndrome doesn’t present any symptoms and hence, there’s no need for an invasive check or treatment. However, in some people, this condition can cause symptoms of decreased blood flow to the brain or upper extremity (like the arm), which are areas supplied by the subclavian artery. These symptoms can include signs like dizziness or weakness.
What Causes Subclavian Steal Syndrome?
Subclavian steal syndrome, a particular health condition, is most frequently caused by a disease known as atherosclerosis. This disease involves the build-up of fats, cholesterol, and other substances in and on your artery walls. It is often found on the patient’s left side. This is likely because the left subclavian artery, a major blood vessel, is shaped in a way that makes the blood flow turbulent, speeding up the process of atherosclerosis.
There are other risk factors for this condition, which include:
- Takayasu arteritis, a rare type of inflammation in large blood vessels, often seen in young or middle-aged women of Asian ancestry.
- Pressure on the subclavian artery in the chest area, often seen in athletes like cricket bowlers and baseball pitchers, due to the pinching of nerves and vessels as this artery goes over the top rib.
- The existence of a cervical rib, an extra rib that grows from the seventh bone of the neck.
- After having surgery to fix a coarctation of the aorta. The aorta is the main blood vessel in the body, and coarctation is a narrowing that can cause problems with blood flow.
- Born with specific abnormalities, such as a right aortic arch, which means the aorta, the main artery, isn’t in its usual position.
- Rare anatomical factors including a tear in the aorta’s wall, abnormal formation of the vertebral artery, and external pressure on the vertebral artery.
Risk Factors and Frequency for Subclavian Steal Syndrome
The exact occurrence or prevalence of subclavian steal syndrome is not precisely known. From the data we have, its prevalence is believed to be somewhere between 0.6% and 6.4%. In a joint study looking at blockages in arteries outside of the brain, subclavian steal syndrome was found in 2.5% of cases. However, only a small number of these, around 5.3%, had any neurological symptoms. The syndrome is more common in males than in females, with about twice as many males affected, often due to hardening of the arteries.
Signs and Symptoms of Subclavian Steal Syndrome
Subclavian artery stenosis is a condition where the subclavian artery, which is a major blood vessel in your body, becomes narrowed. Most people with subclavian artery stenosis don’t have any noticeable symptoms. Sometimes, the condition is discovered accidentally when a difference in blood pressure is noticed between the arms or through an ultrasound test performed for other heart-related diseases.
However, some patients may experience symptoms like arm pain, fatigue, numbness, or unusual sensations (paresthesias). These symptoms occur due to the lack of blood flow (ischemia) to the arms during intense physical activity. The condition can also cause a range of neurological symptoms due to insufficient blood supply to the brain (vertebrobasilar insufficiency). These include dizziness, blurred vision, fainting, vertigo, balance issues, uncoordinated movements, ringing in the ears, or hearing loss. These symptoms can be brought on by exercise involving the arms or certain head movements, such as turning the face to the opposite side. A thorough review of the patient’s history can aid in diagnosing this condition.
On physical examination, a difference of at least 15 mmHg in blood pressure can be observed between the affected and the normal arm. Feeling the radial pulse in both arms at the same time may reveal a weaker pulse and a longer time to detect the pulse on the affected side. An examination of the carotid arteries on both sides through touch and listening with a stethoscope can also be helpful in identifying if the disease is present. The subclavian arteries should also be examined in the area above the collarbone (supraclavicular fossa) through palpation and auscultation for abnormal sounds (bruits).
Testing for Subclavian Steal Syndrome
If your symptoms match what is commonly known as the subclavian steal syndrome, the first test a doctor usually recommends is a duplex ultrasound. This is a simple and non-invasive test, meaning it doesn’t require any surgical procedures. It’s helpful not only for diagnosing the issue but also for measuring the degree of narrowing in the subclavian artery, the main blood vessel of your upper body. If this test reveals that blood is flowing at a speed greater than 240 cm/second through the subclavian artery, it is an indicator of significant constriction or blockage. However, it’s important to remember, this test might not provide a complete picture of the blood vessels’ origin leading to the brain.
Magnetic resonance angiography, or MRA, is another highly accurate technique for diagnosing this condition. This test can provide a detailed image of both the blood vessels inside your brain and those leading to the brain (extracranial vessels).
CT angiography is yet another way to determine if you have subclavian steal syndrome, especially if your duplex ultrasound results were unclear or abnormal. This test helps to identify and classify the level of any bottlenecks in the subclavian artery.
Finally, to decide the best treatment option, your doctor might recommend further testing. Although the duplex ultrasound is very helpful, it’s typically followed up with a more specific scan known as a contrast-enhanced MRA or a CT angiography. These tests provide more detailed information and can guide the doctor in their decisions about treatment. If a procedure called stenting (inserting a small tube to keep the artery open) is being considered, a special test called digital subtraction angiography (DSA) may be preferred. DSA often provides even better details about any physical obstacles in the artery.
Treatment Options for Subclavian Steal Syndrome
Many patients with subclavian artery stenosis, a condition that involves the narrowing of the artery near the neck or shoulder, may not need immediate medical treatment. They might have no symptoms, or only mild symptoms that get better on their own over time.
Subclavian artery stenosis can be a sign of an underlying health issue known as atherosclerosis, where the arteries become clogged with fatty substances. This means that patients with this condition may have a higher risk of developing heart disease or stroke. These patients can benefit from preventive care, which may include controlling high blood pressure, treating high cholesterol, quitting smoking, managing diabetes, and making healthy lifestyle changes.
For those who do have symptoms, surgery to bypass the blocked artery, referred to as an “open surgical bypass”, can be an option. The most common type of surgery used to treat this condition is called “extra-anatomic revascularization,” such as carotid transposition or carotid-subclavian bypass.
Alternatively, if the blockage is short or close to the surface, a less invasive procedure known as endovascular intervention may be considered. This uses special tools passed through a thin tube to open up the blocked artery. About 10% of patients can experience a blockage that is less than 70% of the artery’s width. These individuals can benefit greatly from a procedure called angioplasty, where a tiny balloon is used to open up the blocked area. Around 5% of these patients may need to have surgery eventually.
For those who aren’t able to have surgery or endovascular intervention, medication options also exist. For instance, antiplatelet therapy (which prevents blood clots) and oral anticoagulation (which thins the blood) can be trialed for patients with a high risk of surgical complications or if the anatomy of their artery doesn’t allow for surgical procedures. However, the effectiveness of this approach hasn’t been thoroughly studied yet.
What else can Subclavian Steal Syndrome be?
There are many different conditions that might be confused with Subclavian Steal Syndrome (SSS), but can be differentiated by specific symptoms and diagnostic tests. Here are some of them:
- Peripheral Arterial Disease (PAD) of the Upper Extremity: This condition could be due to a clot, inflammation of the artery, or abnormal development of the connective tissue within the artery. It can cause pain during exercise, pain even without activity or sores on the fingers. Sometimes, the only sign could be differences in blood pressure readings between the two arms. However, it doesn’t cause neurological symptoms like SSS.
- Posterior Circulation Stroke: This can cause fainting, dizziness, blurred vision, or problems with coordination. Tests like MRI or CT scan of the arteries can help identify whether it’s this condition or SSS.
- Aortic Stenosis: This condition should be considered if a patient is fainting. It’s essential to rule out this and other heart-related causes. If a certain kind of whooshing sound (called systolic murmur) is heard from the heart with a stethoscope, it might suggest Aortic Stenosis. An ultrasound of the heart (echocardiogram) can confirm this diagnosis.
- Diabetic Neuropathy: This condition may cause symptoms that are typically felt on both sides of the body, and often start in the hands and feet. This pattern of symptoms might suggest that it’s neuropathy and not SSS. Electromyography, which is a kind of nerve test, can help confirm this diagnosis.
What to expect with Subclavian Steal Syndrome
Subclavian steal syndrome is generally a harmless condition. However, it can be a sign of atherosclerosis, a disease where plaque builds up inside your arteries. This could hint at the possibility of potential serious issues in the future, such as a myocardial ischemia, a condition where there’s reduced blood flow to the heart, or a stroke.
But, preventative measures can help patients maintain a good prognosis, which means they may have positive health outcomes.
If patients show symptoms and go through surgery with angioplasty (widening of blocked arteries) and stenting (placement of a small mesh tube to open up blood vessels), or open surgical bypass (creating a new pathway for blood flow), they generally have a good prognosis.
In fact, most patients (over 95%) see a lasting relief from symptoms related to decreased blood flow and do not require any further intervention on the affected blood vessel.
Possible Complications When Diagnosed with Subclavian Steal Syndrome
Subclavian steal syndrome, on its own, doesn’t seem to result in any long-term problems. However, it can lead to a condition known as vertebrobasilar insufficiency. This can cause episodes of fainting, which may result in falls. These falls could then potentially lead to a head injury.
In a case called coronary-subclavian steal, the blood reverses its usual flow. It moves from the graft in the coronary artery to the subclavian circulation. This abnormal flow can result in a shortage of blood in the heart muscle – a condition called myocardial ischemia.
Common Risks:
- Vertebrobasilar insufficiency
- Fainting episodes
- Potential falls
- Risk of head injury
- Coronary-subclavian steal
- Myocardial ischemia – shortage of blood in the heart muscle
Preventing Subclavian Steal Syndrome
If you have a condition that prevents normal blood flow in a certain part of your body, it’s important to limit exercise of that area to avoid worsening the situation. This condition, known as subclavian steal syndrome, can be managed more effectively if patients also take other precautionary steps. These include quitting smoking, regulating blood sugar levels, controlling blood pressure, and making healthy lifestyle changes. These measures can help prevent further health problems related to this condition.
