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How does Brain Attack, Cerebrovascular Accident - CVA occur? Print E-mail
Written by Amanda Wattson, MD   
Thursday, 08 October 2009
A stroke is the death of brain tissue that occurs when the brain does not get enough blood and oxygen.
What is going on in the body?

Strokes are classified as ischemic strokes or hemorrhagic strokes. Ischemic strokes happen when the blood supply to the brain is interrupted. The brain cells then die from lack of oxygen. Hemorrhagic strokes occur when blood vessels in the brain burst and release blood into the area around the brain cells. The blood then damages the brain cells. The products released when cells die cause swelling in the brain. Since the skull doesn't allow much room for expansion, this swelling can damage the brain tissue even further.

Examples of ischemic strokes are:
- stroke from atherosclerosis, which occurs when the arteries supplying the brain are narrowed by plaque formation on the vessel walls
- stroke from carotid stenosis, which is a blockage in one of the carotid arteries in the neck
- arteritis, or artery inflammation, in an artery that supplies the brain. This may be due to a condition called temporal arteritis, for example.
- stroke from carotid dissection. A carotid dissection occurs when one of the carotid arteries in the neck is torn by an injury and blood flow to the brain is blocked.
- polycythemia vera, a blood cancer that causes blood cells to multiply and the blood to thicken. The thickened blood prevents normal oxygenation of brain cells.
- stroke from cardiogenic embolism, a condition in which blood clots travel from the heart. Blood clots from the heart may be caused by an irregular heartbeat called atrial fibrillation, severe congestive heart failure, and heart attack.
- stroke caused by cholesterol or plaque from an artery in the neck. When the cholesterol or plaque travels and blocks an artery supplying the brain, a stroke occurs.
- severe migraine headaches, which cause constriction of the blood vessels within the brain and deprive brain cells of oxygen

Hemorrhagic strokes occur when there is bleeding into the brain caused by damage to the blood vessels. A hemorrhagic stroke may be caused by:
- high blood pressure
- abnormal bleeding from blood-thinning medications, such as warfarin or heparin
- hemophilia A or hemophilia B, which are blood disorders that prevent normal blood clotting
- low numbers of platelets, a type of blood cell involved in blood clotting. Low platelet counts are seen in a number of diseases and conditions, including acute infections and a severe allergic reaction known as anaphylactic shock.
- rupture of a cerebral aneurysm, or weakened blood vessel wall within the brain
- sickle cell disease, an inherited condition that results in abnormal red blood cells
- a group of abnormal blood vessels within the brain known as an arteriovenous malformation, or AVM
- head injuries
- eclampsia, a complication of pregnancy that causes high blood pressure in the mother

Stroke is the third leading cause of death in the US and many other countries, right after heart disease and cancer.
What are the causes and risks of the condition?

Strokes are caused by an interruption of the blood flow to brain cells or by damage to brain cells.

The American Heart Association has recently issued guidelines for stroke prevention. The guidelines discuss risk factors for stroke in 3 categories: nonmodifiable, well-documented modifiable, and less well-documented or potentially modifiable.

The nonmodifiable factors are ones that cannot be changed by the individual and include:
- increasing age. A person's risk of stroke doubles each year after age 55.
- race. Strokes occur approximately twice as often in blacks and Hispanics as they do in whites.
- gender. Men have a 50% higher chance of stroke than women do.
- family history of stroke or transient ischemic attack (TIA). A TIA is a short, reversible form of stroke that may serve as an early warning sign of stroke.

Well-documented modifiable risk factors are those that can be changed by the individual in conjunction with his or her healthcare provider.
These factors are linked to stroke by strong research findings, and there is documented proof that changing the risk factor lowers a person's risk of stroke. These factors include:
- high blood pressure
- smoking
- diabetes
- asymptomatic carotid stenosis, or narrowing of one of the arteries in the neck
- sickle cell anemia, a blood disorder that forms abnormal red blood cells
- high cholesterol levels in the blood, including total cholesterol and LDL or "bad cholesterol." Low levels of HDL or "good cholesterol" are also cause for concern.
- atrial fibrillation, an abnormal heart rhythm

Less well-documented or potentially modifiable risk factors for stroke are those that have less proof of either a link to stroke or the impact of modifying the risk factor. These factors include:
- obesity
- sedentary lifestyle
- alcohol abuse
- high blood levels of homocysteine, a blood component sometimes associated with a higher risk of stroke
- drug abuse
- blood disorders, such as blood that clots easily or deficiencies of various blood components
- hormone replacement therapy (HRT). The AHA currently states that the risk of stroke associated with HRT appears low but needs further study.
- use of birth control pills, or oral contraceptives
- inflammatory processes, such as a chronic infection with chlamydia

Several recent studies have identified factors that seem to increase or decrease the risk of stroke in particular groups of people. These studies, which warrant further investigation, include these findings:
- People who were treated for high blood pressure with thiazide diuretics, such as hydrochlorothiazide, had a significantly lower stroke risk than people on ACE inhibitors or calcium channel blockers.
- Women ages 39 to 50 who ate more fish and omega-3 polyunsaturated fatty acids had a reduced risk of ischemic stroke. This was particularly true in women who did not take aspirin regularly.
- Women ages 15 to 44 who had 2 drinks of wine a day had a 40% to 60% lower risk of stroke than women who did not drink alcohol.
- Phenylpropanolamine, a compound contained in appetite suppressants and cold remedies, significantly increased the risk of hemorrhagic stroke in women 18 to 49 years of age. The Food and Drug Administration (FDA) has since asked manufacturers to remove phenylpropanolamine from their products.
- In one study, people who were treated in emergency departments for transient ischemic attacks (TIA) had a 25% chance of having a stroke or other serious health event within the next 90 days.

What are the treatments for the condition?

Most people with strokes are treated right away with only aspirin if they do not have bleeding into the brain. This only serves to help prevent further strokes. In cases when a stroke is caught in the first few hours, a clot-busting medication may be used to reverse a stroke. This is why early recognition of a stroke can be important.

If someone has the early warning signs of stroke, the emergency medical system should be contacted immediately.

These signs include a sudden onset of:
- severe headache
- weakness or numbness of the face, arm, or leg, especially on one side of the body
- dizziness
- trouble walking or loss of balance, known as ataxia
- confusion
- speech impairments, including trouble speaking or understanding speech
- visual impairments

Specific types of medication may be needed in special cases. For instance, those with a heart infection may be given antibiotics. Those with arteritis are often given corticosteroids, such as prednisone, to reduce inflammation in the brain.

If an individual has significant narrowing of the carotid arteries, a carotid endarterectomy may be recommended to widen them. This surgical procedure removes the cholesterol plaques and may prevent future strokes. The decision to perform surgery will depend on the person's neurological status, the type of plaque clogging the artery, and whether the plaque has a break in it, known as a rupture.

Supportive therapy may also be needed with some strokes. This may include an artificial breathing machine, or ventilator, and an artificial feeding tube if the person cannot swallow.

Rehabilitation services can help to improve a person's function after a stroke. Physical therapy and other therapy, such as speech therapy or occupational therapy, may be used to maximize recovery.
What are the side effects of the treatments?

Side effects depend on the treatments used. For instance, aspirin may cause allergic reactions, stomach upset, or bleeding. Clot-busting medications can cause excessive bleeding. A ventilator may sometimes cause damage to the lungs or an infection.

A carotid artery endarterectomy can cause bleeding, infections, and allergic reactions to the anesthesia. On rare occasions, carotid endarterectomy can cause a stroke or heart attack to occur.
What happens after treatment for the condition?

After the person is stable, treatment of the risk factors for stroke, as well as the cause of the stroke, is important to prevent further strokes. For instance, stopping smoking and controlling high blood pressure, diabetes, and high cholesterol are advised for most people.

Those with arteritis are often maintained on medications to reduce inflammation for long periods. Those with clots in the heart are often put on medications to thin the blood, such as warfarin.

Many people need assistance of one form or another after a stroke. This may range from using a walking cane to needing 24-hour-a-day skilled nursing care. Ongoing therapy to improve function is usually advised for at least 6 months if the person is able.
 

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