Stroke

What is a stroke?

A stroke, or cerebrovascular accident (CVA), occurs when blood supply to part of the brain is disrupted, causing brain cells to die. When blood flow to the brain is impaired, oxygen and glucose cannot be delivered to the brain. Blood flow can be compromised by a variety of mechanisms.

Blockage of an artery

• Narrowing of the small arteries within the brain can cause a so-called lacunar stroke, (lacune=empty space). Blockage of a single arteriole can affect a tiny area of brain causing that tissue to die (infarct).
  
  
• Hardening of the arteries (atherosclerosis) leading to the brain. There are four major blood vessels that supply the brain with blood. The anterior circulation of the brain that controls most motor, activity, sensation, thought, speech, and emotion is supplied by the carotid arteries. The posterior circulation, which supplies the brainstem and the cerebellum, controlling the automatic parts of brain function and coordination, is supplied by the vertebrobasilar arteries.

If these arteries become narrow as a result of atherosclerosis, plaque or cholesterol, debris can break off and float downstream, clogging the blood supply to a part of the brain. As opposed to lacunar strokes, larger parts of the brain can lose blood supply, and this may produce more symptoms than a lacunar stroke.

• Embolism to the brain from the heart. In situations in which blood clots form within the heart, the potential exists for small clots to break off and travel (embolize) to the arteries in the brain and cause a stroke.

Rupture of an artery (hemorrhage)

• Cerebral hemorrhage (bleeding within the brain substance). The most common reason to have bleeding within the brain is uncontrolled high blood pressure. Other situations include aneurysms that leak or rupture or arteriovenous malformations (AVM) in which there is an abnormal collection of blood vessels that are fragile and can bleed.

What causes a stroke?

Blockage of an artery

The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. As a result of the deprived blood and oxygen, the cells of that part of the brain die. Typically, a clot forms in a small blood vessel within the brain that has been previously narrowed due to a variety of risk factors including:

• high blood pressure (hypertension),
  
• high cholesterol,
  
• diabetes, and
  
• smoking.

Embolic stroke

Another type of stroke may occur when a blood clot or a piece of atherosclerotic plaque (cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose, travels through open arteries, and lodges in an artery of the brain. When this happens, the flow of oxygen-rich blood to the brain is blocked and a stroke occurs. This type of stroke is referred to as an embolic stroke. For example, a blood clot might originally form in the heart chamber as a result of an irregular heart rhythm, such as occurs in atrial fibrillation. Usually, these clots remain attached to the inner lining of the heart, but occasionally they can break off, travel through the blood stream, form a plug (embolism) in a brain artery, and cause a stroke. An embolism can also originate in a large artery (for example, the carotid artery, a major artery in the neck that supplies blood to the brain) and then travel downstream to clog a small artery within the brain.

Cerebral hemorrhage

A cerebral hemorrhage occurs when a blood vessel in the brain ruptures and bleeds into the surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) can cause a stroke by depriving blood and oxygen to parts of the brain. Blood is also very irritating to the brain and can cause swelling of brain tissue (cerebral edema). Edema and the accumulation of blood from a cerebral hemorrhage increases pressure within the skull and causes further damage by squeezing the brain against the bony skull.

Subarachnoid hemorrhage

In a subarachnoid hemorrhage, blood accumulates in the space beneath the arachnoid membrane that lines the brain. The blood originates from an abnormal blood vessel that leaks or ruptures. Often this is from an aneurysm (an abnormal ballooning out of the wall of the vessel). Subarachnoid hemorrhages usually cause a sudden, severe headache and stiff neck. If not recognized and treated, major neurological consequences, such as coma, and brain death will occur.

Vasculitis

Another rare cause of stroke is vasculitis, a condition in which the blood vessels become inflamed. 

Migraine headache

There appears to be a very slight increased occurrence of stroke in people with migraine headache. The mechanism for migraine or vascular headaches includes narrowing of the brain blood vessels. Some migraine headache episodes can even mimic stroke with loss of function of one side of the body or vision or speech problems. Usually, the symptoms resolve as the headache resolves. 

What are the risk factors for stroke?

Overall, the most common risk factors for stroke are:

• high blood pressure,
  
• high cholesterol,
  
• smoking,
  
• diabetes and
  
• increasing age.

Heart rhythm disturbances like atrial fibrillation, patent foramen ovale, and heart valve disease can also be the cause.

When strokes occur in younger individuals (less than 50 years old), less common risk factors are considered including illicit drugs, such as cocaine or amphetamines, ruptured aneurysms, and inherited (genetic) predispositions to blood clotting. 

An example of a genetic predisposition to stroke occurs in a rare condition called homocystinuria, in which there are excessive levels of the chemical homocystine in the body. Scientists are trying to determine whether the non-hereditary occurrence of high levels of homocystine at any age can predispose to stroke.

What is a transient ischemic attack (TIA)?

A transient ischemic attack (TIA) is a short-lived episode (less than 24 hours) of temporary impairment to the brain that is caused by a loss of blood supply. A TIA causes a loss of function in the area of the body that is controlled by the portion of the brain affected. The loss of blood supply to the brain is most often caused by a clot that spontaneously forms in a blood vessel within the brain (thrombosis). However, it can also result from a clot that forms elsewhere in the body, dislodges from that location, and travels to lodge in an artery of the brain (emboli). A spasm and, rarely, a bleed are other causes of a TIA. Many people refer to a TIA as a "mini-stroke."

What is the impact of strokes?

In the United States, stroke is the third largest cause of death (behind heart disease and all forms of cancer). The cost of strokes is not just measured in the billions of dollars lost in work, hospitalization, and the care of survivors in nursing homes. The major cost or impact of a stroke is the loss of independence that occurs in 30% of the survivors. What was a self-sustaining and enjoyable lifestyle may lose most of its quality after a stroke and other family members can find themselves in a new role as caregivers.

What are stroke symptoms?

When brain cells are deprived of oxygen, they cease to perform their usual tasks. The symptoms that follow a stroke depend on the area of the brain that has been affected and the amount of brain tissue damage.

Small strokes may not cause any symptoms, but can still damage brain tissue. These strokes that do not cause symptoms are referred to as silent strokes. According to The U.S. National Institute of Neurological Disorders and Stroke (NINDS), these are the five major signs of stroke:

1. Sudden numbness or weakness of the face, arm or leg, especially on one side of the body. The loss of voluntary movement and/or sensation may be complete or partial. There may also be an associated tingling sensation in the affected area.
2. Sudden confusion or trouble speaking or understanding. Sometimes weakness in the muscles of the face can cause drooling.
3. Sudden trouble seeing in one or both eyes
4. Sudden trouble walking, dizziness, loss of balance or coordination
5. Sudden, severe headache with no known cause 

What should be done if you suspect you or someone else is having a stroke?

If any of the symptoms mentioned above suddenly appear, emergency medical attention should be sought. Therefore, the first action should be to call 911 (or whatever number activates the emergency medical response in your area). The family doctor and/or neurologist should also be contacted. However, the first priority is ensuring that the ambulance arrives as soon as possible.

• The affected person should lie flat to promote an optimal blood flow to the brain.
  
  
• If drowsiness, unresponsiveness, or nausea are present, the person should be placed in the rescue position on their side to prevent choking should vomiting occur.
  
  
• Although aspirin plays a major role in stroke prevention (see below), once the symptoms of a stroke begin, it is generally recommended that additional aspirin not be taken until the patient receives medical attention. If stroke is of the bleeding type, aspirin could theoretically make matters worse.

How is a stroke diagnosed?

A stroke is a medical emergency. Anyone suspected of having a stroke should be taken to a medical facility immediately for evaluation and treatment. Initially, the doctor takes a medical history from the patient if he/she is alert or others familiar with the patient if they are available, and performs a physical examination. If a person has been seeing a particular doctor, it would be ideal for that doctor to participate in the assessment. Previous knowledge of the patient can improve the accuracy of the evaluation. A neurologist, a doctor specializing in disorders of the nervous system and diseases of the brain, will often assist in the diagnosis and management of stroke patients.

Just because a person has slurred speech or weakness on one side of the body does not necessarily signal the occurrence of a stroke. There are many other possibilities that can be responsible for these symptoms. Other conditions that can mimic a stroke include:

• brain tumors,
  
• a brain abscess (a collection of pus in the brain caused by bacteria or a fungus),
  
• migraine headache,
  
• bleeding in the brain either spontaneously or from trauma,
  
• meningitis or encephalitis,
  
• an overdose of certain medications, or
  
• an imbalance of sodium, calcium, or glucose in the body can also cause changes in the nervous system that can mimic a stroke.

What is the treatment of a stroke?

Tissue plasminogen activator (TPA)

There is opportunity to use alteplase (TPA) as a clot-buster drug to dissolve the blood clot that is causing the stroke. There is a narrow window of opportunity to use this drug. The earlier that it is given, the better the result and the less potential for the complication of bleeding into the brain.

Present American Heart Association guidelines recommend that if used, TPA must be given within three hours after the onset of symptoms. Normally, TPA is injected into a vein in he arm. The time frame for use can be extended to six hours if it is dripped directly into the blood vessel that is blocked. This is usually performed by an interventional radiologist, and not all hospitals have access to this technology.

For posterior circulation strokes that involve the vertebrobasilar system, the time frame for treatment with TPA may be extended even further to 18 hours.

Heparin and aspirin

Drugs to thin the blood (anticoagulation; for example, heparin) are also sometimes used in treating stroke patients in the hopes of improving the patient's recovery. It is unclear, however, whether the use of anticoagulation improves the outcome from the current stroke or simply helps to prevent subsequent strokes (see below). In certain patients, aspirin given after the onset of a stroke does have a small, but measurable effect on recovery. The treating doctor will determine the medications to be used based upon a patient's specific needs.

Managing other Medical Problems

 

Blood pressure and cholesterol control are key to prevention of future stroke events. In transient ischemic attacks, the patient may be discharged with medications even if the blood pressure and cholesterol levels are acceptable. In an acute stroke, blood pressure will be tightly controlled to prevent further damage.

In patients with diabetes, the blood sugar (glucose) level is often elevated after a stroke. Controlling the glucose level in these patients may minimize the size of a stroke. Finally, oxygen may administered to stroke patients when necessary.

Rehabilitation

When a patient is no longer acutely ill after a stroke, the healthcare staff focuses on maximizing the patient's functional abilities. This is most often done in an inpatient rehabilitation hospital or in a special area of a general hospital. Rehabilitation can also take place at a nursing facility.

The rehabilitation process can include some or all of the following:

1. speech therapy to relearn talking and swallowing;
   
2. occupational therapy to regain dexterity in the arms and hands;
   
3. physical therapy to improve strength and walking; and
   
4. family education to orient them in caring for their loved one at home and the challenges they will face.

What can be done to prevent a stroke?

Risk factor reduction 

High blood pressure: The possibility of suffering a stroke can be markedly decreased by controlling the risk factors. The most important risk factor for stroke is high blood pressure. When a person's blood pressure is persistently too high, roughly greater than 130/85, the risk of a stroke increases in proportion to the degree by which the blood pressure is elevated. Controlling blood pressure in the normal range decreases the chances of a stroke. 

Smoking: Another important risk factor is cigarette or other tobacco use. Cigarettes cause the carotid arteries to develop severe atherosclerosis, which can lead to their closure and block the blood flow to the brain. Atherosclerosis in general, including involvement of the arteries that supply blood to the heart, is accelerated by smoking. So, when an individual smokes, the main question becomes - which will occur first; a stroke, heart attack, or lung cancer?

Diabetes: Another risk factor for developing a stroke is diabetes mellitus. Diabetes causes the small vessels to close prematurely. When these blood vessels close in the brain, small (lacunar) strokes may occur. Good control of blood sugar is important in decreasing the risk of stroke in diabetic patients. An elevated level of blood cholesterol is also a risk factor for a stroke due to the eventual blockage of blood vessels (atherosclerosis). A healthy diet and medications can help normalize an elevated blood cholesterol level. 

Blood thinner/warfarin: An irregular heart beat (atrial fibrillation in particular) is associated with an increased risk of an embolic stroke, in which the blood clot travels from the heart, through the bloodstream, and into the brain. Warfarin (Coumadin) is a blood "thinner" that prevents the blood from clotting. This medication is often used in patients with atrial fibrillation to decrease this risk. Warfarin is also sometimes used to prevent the recurrence of a stroke in other situations, such as with certain other heart conditions and conditions in which the blood has a tendency to clot on its own (hypercoagulable states). Patients taking warfarin need to have periodic blood checks to make sure that their current dose is producing the desired effect. Patients on warfarin also need to know that they are at increased risk for bleeding, either externally or internally.

Aspirin and other antiplatelet therapy: Many stroke patients who do not require warfarin can use another class of medicines called "antiplatelet" drugs to reduce their risk of suffering another stroke. These medicines reduce the tendency of the blood to clot (clog) in the arteries. As a side effect, patients on these medicines usually have a higher likelihood of bleeding, but this risk is less than when taking an anticoagulant like warfarin. The most commonly prescribed first-choice antiplatelet agent for preventing a stroke recurrence is aspirin. If the patient has an adverse reaction to aspirin or has a stroke despite being on aspirin, newer antiplatelet preparations can be used [clopidogrel (Plavix), dipyridamole (Persantine). 

Carotid endarterectomy: In many cases, a person may suffer a TIA or a stroke that is caused by the narrowing or ulceration (sores) of the carotid arteries (the major arteries in the neck that supply blood to the brain). If left untreated, patients with these conditions have a high risk of experiencing a major stroke in the future. An operation that cleans out the carotid artery and restores normal blood flow is known as a carotid endarterectomy. This procedure has been shown to markedly reduce the incidence of a subsequent stroke. In patients who have a narrowed carotid artery, but no symptoms, this operation may be indicated in order to prevent the occurrence of a first stroke. 

 Stroke at a Glance

• Stroke is the sudden death of brain cells due to lack of oxygen.
  
  
• Stroke is caused by the blockage of blood flow or rupture of an artery to the brain.
  
  
• Sudden tingling, weakness, or paralysis on one side of the body or difficulty with balance, speaking, swallowing, or vision can be a symptom of a stroke.
  
  
• Any person suspected of having a stroke or TIA should present for emergency care immediately
  
  
• Clot-busting drugs like TPA can be used to reverse a stroke, but the time frame for their use is very narrow. Patients need to present for care as soon as possible so that TPA therapy can be considered.
  
  
• Stroke prevention involves minimizing risk factors, such as controlling high blood pressure, elevated cholesterol, tobacco abuse, and diabetes. 
  

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