Subclavian steal syndrome describes a group of symptoms that occur as the result of an obstruction in one of the large arteries that provide the arms with oxygenated blood. This shortage causes blood to be taken or stolen from the arteries that supply the patient's brain. The obstruction in the subclavian artery is typically caused by atherosclerosis-related emboli, but other uncommon cases can be caused by thoracic outlet syndrome, shunt displacement, blood clots, and large artery vasculitis.
Subclavian steal syndrome is diagnosed with the use of MRI imaging, CT scan, ultrasound echo testing, physical exam, and evaluation of vital signs. Subclavian steal syndrome is a form of peripheral artery disease, which is any condition where arteries outside of the heart become narrowed. Subclavian steal syndrome is treated using the same methods utilized in other forms of peripheral artery disease, including lifestyle changes, angioplasty and stenting, surgical bypass, and medications.
Subclavian steal syndrome patients may experience fainting (syncope). Directly branching from an individual's aorta, two subclavian arteries supply oxygenated blood to the arms and the left common carotid artery that provides oxygenated blood to the anterior brain and skull. From the subclavian arteries, one vertebral artery branches off each and eventually merge to provide oxygenated blood to the posterior brain. When some mechanism blocks one of the subclavian arteries between the aorta and the origin of the vertebral artery, a lack of blood flow to the arm of the affected side siphons blood from the opposite vertebral artery supply to the brain. This process is what characterizes subclavian steal syndrome.
This mechanism is made possible because both vertebral arteries come together at the base of the brain in a network called the circle of Willis. Consciousness is dictated by several parts of the brain, but the brain stem carries the heaviest burden. When part of the brain stem's supply of oxygenated blood is being stolen by the subclavian artery, the cells in that area are unable to keep the patient in a conscious state. This malfunction results in the affected individual having fainting spells. An estimated eighteen percent of individuals affected by this syndrome have this symptom.
Hands With Circulation Issues
Individuals affected by subclavian steal syndrome may have hands with circulation issues. This occurs due to the reduced supply of blood to the arm when the subclavian artery becomes fully or partially obstructed. This symptom occurs in patients who overexert their affected arm with exercise or occupation related movements. This symptom is confirmed by measuring blood pressure in both arms and observing the difference. Symptoms of ischemia in the brain stem and brain are more common than circulation issues in the hands of affected individuals.
Although the subclavian artery steals blood, the supply sometimes does not end up being enough to provide oxygen to all of the vessels in the arms and hands. Patients who have circulation problems in their hands precipitated from subclavian steal syndrome can experience claudication, or pain due to a lack of oxygen to the muscle cells. Muscle weakness can occur in the hands due to a lack of sufficient blood flow as well as paresthesia. The hands may turn white or blue in response to poor circulation or feel cold to the touch.
Subclavian steal syndrome patients can experience lightheadedness or unsteadiness. This symptom is different than vertigo, even though both are associated with each other. Vertigo has a component of spinning to it while lightheadedness does not. The lack of blood supply from the vertebral arteries can cause the part of the brain called the cerebellum to be starved of oxygen. The cerebellum is the part of the brain responsible for functions such as posture, balance, and movement coordination. These functions may become compromised, resulting in lightheadedness.
Additionally, the brain stem is also fed oxygenated blood by the vertebral arteries and may become starved of oxygen in affected individuals. The brain stem is responsible for the regulation of many autonomous nervous functions, including blood pressure, heart rate, breathing, and consciousness. Lightheadedness may occur as a result of the cells in the brain stem shutting down because of an inadequate supply of oxygen. If these cells continue to be deprived of oxygen following the onset of lightheadedness, the affected individual may lose consciousness.
Approximately half of all individuals affected by subclavian steal syndrome experience vertigo. This occurs when either the balance organs of the inner ear or the parts of the central nervous system responsible for processing spatial information and balance are not functioning properly. While dizziness and lightheadedness are the results of disequilibrium, vertigo is more caused by the altered perception of the movement of the body itself or the environment around the body.
An affected individual can experience vertigo if the cells in the occipital lobe, parietal lobe, and cerebellum do not receive enough blood because of subclavian steal syndrome. Vertigo is most commonly described as spinning or an unsteady feeling with rotational features. The patient can feel like their own body is moving due to altered perception from deprived tissues, or they may interpret this as a feeling the objects around them are moving in a rotational pattern around them. Some individuals compare the feeling of vertigo to motion sickness that occurs when on a boat or long car ride.
Double vision may manifest in subclavian steal syndrome patients. Double vision is best described as when an individual sees two images of the same object when they should only be seeing one. The images the individual is seeing can be on top of one another, side by side, or both. Double vision in patients with subclavian steal syndrome typically occurs in both eyes or is binocular. The reduced blood supply to the brain can cause tissues located in the parietal lobe and the occipital lobe to shut down or begin to die. The occipital lobe is responsible for taking visual information from nerve signals and creating an image in the brain.
The parietal lobe controls many functions, including that of perception, which can alter the way the eyes work. Oxygen deprivation from poor blood supply may also adversely affect the motor area of the brain and the brain stem, resulting in vision disturbances like double vision. Less commonly, the actual nerves that communicate between the tissues of the eye and the brain can become impaired from a lack of oxygen supply due to subclavian steal syndrome. If the eyes fall out of coordination with each other because of problems with nerves or muscle movement in the brain, double vision may occur.
Issues With Memory
Two subclavian arteries branch from the aorta to supply blood to each one of the arms. Each subclavian artery branches into a vertebral artery that carries blood to the base of the brain. An obstruction can occur in one of the subclavian arteries before the branching off of the vertebral artery as a complication of atherosclerosis. This obstruction causes blood flow to the subclavian and vertebral artery to halt. The blood in the brain at the end of the vertebral arteries enters into a structure named the circle of Willis.
During this type of blockage in the subclavian artery, the circle of Willis initiates the reverse of blood flow from the brain back to the arm to help supply the tissues of the limb. This redistribution of blood from the brain to the arm can cause a decrease in the amount of oxygen and nutrients received by some brain tissues, causing them to shut down. Issues with memory occur when certain parts of the brain do not receive enough oxygen due to the blood being stolen from the brain by the subclavian artery.
Subclavian steal syndrome is caused by a condition referred to as atherosclerosis, where a substance called plaque builds up inside of the arterial walls. Plaque is a hard calcified substance made of cholesterol, immune system components, and other fats. A piece of this plaque can break loose from its original location and become lodged in blood vessels around the body. When a piece of plaque becomes lodged in the subclavian artery, it can trigger a mechanism that has adverse effects on the patient's brain tissues.
When an individual's subclavian artery is obstructed, the circle of Willis in the base of the brain can cause blood to be redirected from the brain tissues to the arm via the vertebral artery. When blood is taken away from the brain tissues to help supply the impaired arm, the patient can experience neurological deficits when the brain cells do not get enough oxygen. The patient may experience neurological deficits such as confusion, vertigo, vision loss, and loss of consciousness.
Claudication is a term used to describe when an individual feels muscle cramping, muscle pain, and muscle fatigue when they are physically using their muscles. Claudication has been described by affected individuals as many different sensations in the muscle, including weakness, tiredness, aching, heaviness, deadweight feeling, and burning. These symptoms tend to manifest when the muscles of the affected part of the individual's body are being exercised and dissipate within a couple of minutes at rest.
Arm claudication is a symptom that can develop in a subclavian steal syndrome patient because the blood flow to the muscles and nerves in the affected arm has been obstructed. When the muscles do not receive enough oxygen, they have to carry out energy-making processes in a different way than they usually would. This secondary energy-producing mechanism in the muscle cells is not nearly as efficient and produces different byproducts than the primary mechanism, which causes the patient to experience arm claudication when they are physically using the affected arm.
Dysarthria is a condition where an individual has weaknesses or problems with controlling the muscles they use to create speech. Dysarthria has been described to be similar to speech that is slowed or slurred and is hard to understand. An individual who experiences dysarthria may be unable to speak loud enough or may speak too loudly. They may also exhibit an abnormal or uneven speech rhythm or volume. A patient who has dysarthria may speak in a monotone or have a raspy, nasal, or strained voice.
Dysarthria can occur in subclavian steal syndrome patients due to the mechanism triggered by the circle of Willis when the subclavian artery becomes obstructed. The circle of Willis redirects an individual's blood from their brain tissues to the arm lacking circulation by using the vertebral artery. This mechanism causes some of the brain tissues to be starved of oxygen, causing them to be unable to function. When the blood is stolen from the part of the brain that controls the muscle responsible for producing speech, the patient will experience dysarthria.
Dysphagia occurs when an individual experiences difficulty with swallowing. Swallowing is a mechanism with three different steps and requires the participation and coordination of the muscles in the pharynx, mouth, and esophagus. The group of nerves in the brain that controls these muscles is referred to as the cranial nerves. The cranial nerves are a series of twelve pairs of nerves that branch off from the brainstem at the base of the brain. Tasting, smelling, seeing, moving the face, moving the eyes, shrugging the shoulders, and swallowing are all functions controlled by the cranial nerves.
The swallowing mechanism involves several cranial nerves, including the trigeminal, glossopharyngeal, hypoglossal, facial, and vagus nerves. A subclavian steal syndrome patient may experience malfunctions in these nerves and the precentral gyrus of the brain when the circle of Willis pulls blood from these structures to the arm that is lacking. The shortage of oxygen from poor blood flow causes the cells that control the swallowing centers in the brain and the cranial nerves to shut down, producing dysphagia.