*
Ischemic stroke usually results when an artery to the brain is blocked, often by a blood clot or a fatty deposit due to atherosclerosis.
*
Symptoms occur suddenly and may include muscle weakness, paralysis, lost or abnormal sensation on one side of the body, difficulty speaking, confusion, problems with vision, dizziness, and loss of balance and coordination.
*
Diagnosis is usually based on symptoms and results of a physical examination, imaging tests, and blood tests.
*
Treatment may include drugs to break up blood clots or to make blood less likely to clot and surgery, followed by rehabilitation.
*
About one third of people recover all or most of normal function after an ischemic stroke.
Causes
An ischemic stroke typically results from blockage of an artery that supplies the brain, most commonly a branch of one of the internal carotid arteries.
Commonly, blockages are blood clots (thrombi) or pieces of fatty deposits (atheromas, or plaques) due to atherosclerosis. Such blockages often occur in the following ways:
*
By forming in and blocking an artery: An atheroma in the wall of an artery may accumulate more fatty material and become large enough to block the artery. Or a blood clot can form and block the artery when an atheroma ruptures (Atherosclerosis: How Atherosclerosis DevelopsFigures). Clots tend to form on a ruptured atheroma because the atheroma narrows the artery and slows blood flow through it, like a clogged pipe slows the flow of water. Slow-moving blood is more likely to clot. A large clot can block enough blood flowing through the narrowed artery that brain cells supplied by that artery die.
*
By traveling to another artery: A blood clot in the heart, a piece of an atheroma, or a blood clot in the wall of an artery can break off and travel through the bloodstream (becoming an embolus). The embolus may then lodge in an artery that supplies the brain and block blood flow there. (Embolism refers to blockage of arteries by materials that travel through the bloodstream to another part of the body.) Such blockages are more likely to occur where arteries are already narrowed by fatty deposits.
Several conditions besides rupture of an atheroma can trigger or promote the formation of blood clots, increasing the risk of blockage by a blood clot, such as the following:
*
Heart-related problems: Blood clots may form in the heart or on a heart valve (including artificial valves). Strokes due to such blood clots are most common among people who have recently had heart surgery and people who have a heart valve disorder or an abnormal heart rhythm (arrhythmia), especially a fast, irregular heart rhythm called atrial fibrillation.
*
Blood disorders: Some disorders, such as an excess of red blood cells (polycythemia), make blood thick, increasing the risk of blood clots. Some disorders, such as antiphospholipid syndrome and a high homocysteine level in the blood (hyperhomocysteinemia), make blood more likely to clot.
*
Oral contraceptives: Taking oral contraceptives, particularly those with a high estrogen dose, increases the risk of blood clots.
Another common cause of ischemic strokes is a lacunar infarction. In lacunar infarction, one of the small arteries deep in the brain becomes blocked by a mixture of fat and connective tissue—a blood clot is not the cause. This disorder is called lipohyalinosis and tends to occur in older people with diabetes or poorly controlled high blood pressure. Lipohyalinosis is different from atherosclerosis, but both disorders can cause blockage of arteries. Only a small part of the brain is damaged in lacunar infarction.
Rarely, small pieces of fat from the marrow of a broken long bone, such as a leg bone, are released into the bloodstream. These pieces can clump together and block an artery. The resulting disorder, called fat embolism syndrome, may resemble a stroke.
An ischemic stroke can also result from any disorder that reduces the amount of blood or oxygen supplied to the brain, such as severe blood loss or very low blood pressure. Occasionally, an ischemic stroke occurs when blood flow to the brain is normal but the blood does not contain enough oxygen. Disorders that reduce the oxygen content of blood include a severe deficiency of red blood cells (anemia), suffocation, and carbon monoxide poisoning. Usually, brain damage in such cases is widespread (diffuse), and coma results.
An ischemic stroke can occur if inflammation of blood vessels (vasculitis) or infection (such as herpes simplex) narrows blood vessels that supply the brain. Migraine headaches or drugs such as cocaine and amphetamines can cause spasm of the arteries, which can narrow the arteries supplying the brain and cause a stroke.
Clogs and Clots: Causes of Ischemic Stroke
When an artery that carries blood to the brain becomes clogged or blocked, an ischemic stroke can occur. Arteries may be blocked by fatty deposits (atheromas, or plaques) due to atherosclerosis. Arteries in the neck, particularly the internal carotid arteries, are a common site for atheromas. Arteries may also be blocked by a blood clot (thrombus). Blood clots may form on an atheroma in an artery. Clots may also form in the heart of people with a heart disorder. Part of a clot may break off and travel through the bloodstream (becoming an embolus). It may then block an artery that supplies blood to the brain, such as one of the cerebral arteries.
Symptoms
Usually, symptoms occur suddenly and are often most severe a few minutes after they start because most ischemic strokes begin suddenly, develop rapidly, and cause death of brain tissue within minutes to hours. Then, most strokes become stable, causing little or no further damage. Strokes that remain stable for 2 to 3 days are called completed strokes. Sudden blockage by an embolus is most likely to cause this kind of stroke.
Less commonly, symptoms develop slowly. They result from strokes that continue to worsen for several hours to a day or two, as a steadily enlarging area of brain tissue dies. Such strokes are called evolving strokes. The progression of symptoms and damage is usually interrupted by somewhat stable periods, during which the area temporarily stops enlarging or some improvement occurs. Such strokes are usually due to the formation of clots in a narrowed artery.
Many different symptoms can occur, depending on which artery is blocked and thus which part of the brain is deprived of blood and oxygen Brain Dysfunction: Dysfunction by Location). When the arteries that branch from the internal carotid artery (which carry blood along the front of the neck to the brain) are affected, the following are most common:
*
Blindness in one eye
*
Inability to see out of the same side in both eyes
*
Abnormal sensations, weakness, or paralysis in one arm or leg or on one side of the body
When the arteries that branch from the vertebral arteries (which carry blood along the back of the neck to the brain) are affected, the following are most common:
*
Dizziness and vertigo
*
Double vision
*
Generalized weakness on both sides of the body
Many other symptoms, such as difficulty speaking (for example, slurred speech), impaired consciousness (such as confusion), loss of coordination, and urinary incontinence, can occur.
Severe strokes may lead to stupor or coma. In addition, strokes, even milder ones, can cause depression or an inability to control emotions. For example, people may cry or laugh inappropriately.
If symptoms, particularly impaired consciousness, worsen during the first 2 to 3 days, the cause is often swelling due to excess fluid (edema) in the brain. Symptoms usually lessen within a few days, as the fluid is absorbed. Nonetheless, the swelling is particularly dangerous because the skull does not expand. The resulting increase in pressure can cause the brain to shift, further impairing brain function, even if the area directly damaged by the stroke does not enlarge. If the pressure becomes very high, the brain may be forced downward in the skull, through the rigid structures that separate the brain into compartments. The resulting disorder is called herniation (see Head Injuries:IntroductionFigures).
Strokes can lead to other problems. If swallowing is difficult, people may not eat enough and become malnourished. Food, saliva, or vomit may be inhaled (aspirated) into the lungs, resulting in aspiration pneumonia. Being in one position too long can result in pressure sores and lead to muscle loss. Not being able to move the legs can result in the formation of blood clots in deep veins of the legs and groin (deep vein thrombosis). Clots can break off, travel through the bloodstream, and block an artery to a lung (a disorder called pulmonary embolism). People may have difficulty sleeping. The losses and problems resulting from the stroke may make people depressed.
Diagnosis
Audio
Turbulent Blood Flow
Turbulent Blood Flow
Doctors can usually diagnose an ischemic stroke based on the history of events and results of a physical examination. Doctors can usually identify which artery in the brain is blocked based on symptoms (see Brain Dysfunction:IntroductionFigures). For example, weakness or paralysis of the left leg suggests blockage of the artery supplying the area on the right side of the brain that controls the left leg's muscle movements.
Computed tomography (CT) is usually done first. CT helps distinguish an ischemic stroke from a hemorrhagic stroke, a brain tumor, an abscess, and other structural abnormalities. Doctors also measure the blood sugar level to rule out a low blood sugar level (hypoglycemia), which can cause similar symptoms. If available, diffusion magnetic resonance imaging (MRI), which can detect ischemic strokes within minutes of their start, may be done next.
Identifying the precise cause of the stroke is important. If the blockage is a blood clot, another stroke is very likely unless the underlying disorder is corrected. For example, if blood clots result from an abnormal heart rhythm, treating that disorder can prevent new clots from forming and causing another stroke. Tests for causes may include the following:
*
Electrocardiography (ECG) to look for abnormal heart rhythms
*
Continuous ECG monitoring (done at home or in the hospital—see Symptoms and Diagnosis of Heart and Blood Vessel Disorders: Continuous Ambulatory Electrocardiography) to record the heart rate and rhythm continuously for 24 hours (or more), which may detect abnormal heart rhythms that occur unpredictably or briefly
*
Echocardiography to check the heart for blood clots, pumping or structural abnormalities, and valve disorders
*
Imaging tests—color Doppler ultrasonography, magnetic resonance angiography, CT angiography, or cerebral (standard) angiography—to determine whether arteries, especially the internal carotid arteries, are blocked or narrowed
*
Blood tests to check for anemia, polycythemia, blood clotting disorders, vasculitis, and some infections (such as heart valve infections and syphilis) and for risk factors such as high cholesterol levels or diabetes
Imaging tests enable doctors to determine how narrowed the carotid arteries are and thus to estimate the risk of a subsequent stroke or TIA. Such information helps determine which treatments are needed.
For cerebral angiography, a thin, flexible tube (catheter) is inserted into an artery, usually in the groin, and threaded through the aorta to an artery in the neck. Then, a dye is injected to outline the artery. Thus, this test is more invasive than other tests that provide images of the brain's blood supply. However, it provides more information (see Common Imaging Tests: Angiography). Cerebral angiography may be done before atheromas are removed surgically or when vasculitis is suspected.
Rarely, a spinal tap (lumbar puncture) is done—for example, after CT, when doctors still need to determine whether strokelike symptoms are due to an infection or whether a subarachnoid hemorrhage is present (see Stroke (CVA): Subarachnoid Hemorrhage). This procedure is done only if doctors are sure that the brain is not under excess pressure (usually determined by CT or MRI).
Prognosis
About 10% of people who have an ischemic stroke recover almost all normal function, and about 25% recover most of it. About 40% of people have moderate to severe impairments requiring special care, and about 10% require care in a nursing home or other long-term care facility. Some people are physically and mentally devastated and unable to move, speak, or eat normally. About 20% of people who have a stroke die in the hospital. The proportion is higher among older people. About 25% of people who recover from a stroke have another stroke within 5 years. Subsequent strokes impair function further.
During the first few days after an ischemic stroke, doctors usually cannot predict whether a person will improve or worsen. Younger people and people who start improving quickly are likely to recover more fully. About 50% of people with one-sided paralysis and most of those with less severe symptoms recover some function by the time they leave the hospital, and they can eventually take care of their basic needs. They can think clearly and walk adequately, although use of the affected arm or leg may be limited. Use of an arm is more often limited than use of a leg. Most impairments still present after 12 months are permanent.
Treatment
People who have any symptom suggesting an ischemic stroke should go to an emergency department immediately. The earlier the treatment, the better are the chances for recovery.
The first priority is to restore the person's breathing, heart rate, blood pressure (if low), and temperature to normal. An intravenous line is inserted to provide drugs and fluids when needed. If the person has a fever, it may be lowered using acetaminophen Some Trade Names
TYLENOL
, ibuprofen Some Trade Names
ADVILMOTRIN
, or a cooling blanket. An increase in body temperature by even a few degrees can dramatically worsen brain damage due to an ischemic stroke. Generally, doctors do not immediately treat high blood pressure unless it is very high (over 220/120 mm Hg) because, when arteries are narrowed, blood pressure must be higher than normal to push enough blood through them to the brain. However, very high blood pressure can injure the heart, kidneys, and eyes and must be lowered.
If a stroke is very severe, drugs such as mannitol may be given to reduce swelling and the increased pressure in the brain. Some people need a ventilator to breathe adequately.
Specific treatment of stroke may include drugs to break up blood clots (thrombolytic drugs), drugs to make blood less likely to clot (antiplatelet drugs and anticoagulants), and surgery, followed by rehabilitation.
Thrombolytic (Fibrinolytic) Drugs: In certain circumstances, a drug called tissue plasminogen activator (tPA) is given intravenously to break up clots and help restore blood flow to the brain. Because tPA can cause bleeding in the brain and elsewhere, it should not be given to people with certain conditions, such as the following:
*
A past occurrence of a hemorrhagic stroke, a bulge (aneurysm) in an artery to the brain, other structural abnormalities in the brain, or a brain tumor
*
A seizure when the stroke began
*
A tendency to bleed
*
Recent major surgery
*
Recent bleeding (hemorrhage) in the gastrointestinal or urinary tract
*
A recent head injury or other serious trauma
*
A very high or very low blood sugar level
*
A heart infection
*
Current use of an anticoagulant ( warfarin Some Trade Names
COUMADIN
)
*
A large ischemic stroke
*
Blood pressure that remains high after treatment with an antihypertensive drug
*
Symptoms that are resolving quickly
Before tPA is given, CT is done to rule out bleeding in the brain. To be effective and safe, tPA, given intravenously, must be started within 3 hours of the beginning of an ischemic stroke. After 3 hours, most of the damage to the brain cannot be reversed, and the risk of bleeding outweighs the possible benefit of the drug. However, pinpointing when the stroke began may be difficult. So doctors assume that the stroke began the last time a person was known to be well. For example, if a person awakens with symptoms of a stroke, doctors assume the stroke began when the person was last seen awake and well. Thus, tPA can be used in only a few people who have had a stroke.
If people arrive at the hospital 3 to 6 hours (occasionally, up to 18 hours) after the stroke began, they may be given tPA or another thrombolytic drug. But the drug must be given through a catheter instead. For this treatment, doctors make an incision in the skin, usually in the groin, and insert a catheter into an artery. The catheter is then threaded through the aorta and other arteries, to the clot. The clot is partly broken up with the catheter wire and then injected with tPA. This treatment is usually available only at specialized stroke centers.
Antiplatelet Drugs and Anticoagulants: If a thrombolytic drug cannot be used, most people are given aspirin Some Trade Names
BAYER
(an antiplatelet drug) as soon as they get to the hospital. If symptoms seem to be worsening, anticoagulants such as heparin are occasionally used, but their effectiveness has not been proved. Antiplatelet drugs make platelets less likely to clump and form clots. Anticoagulants inhibit proteins in blood that help it to clot (clotting factors).
Regardless of the initial treatment, long-term treatment usually consists of aspirin Some Trade Names
BAYER
or another antiplatelet drug to reduce the risk of blood clots and thus of subsequent strokes (see Stroke (CVA): Prevention). People who have atrial fibrillation or a heart valve disorder are given anticoagulants (such as warfarin Some Trade Names
COUMADIN
) instead of antiplatelet drugs, which do not seem to prevent blood clots from forming in the heart. Occasionally, people at high risk of another stroke are given both aspirin Some Trade Names
BAYER
and warfarin Some Trade Names
COUMADIN
.
If people have been given a thrombolytic drug, doctors usually wait at least 24 hours before antiplatelet drugs or anticoagulants are started because these drugs add to the already increased risk of bleeding in the brain. Anticoagulants are not given to people who have uncontrolled high blood pressure or who have had a hemorrhagic stroke.
Surgery: Once an ischemic stroke is completed, surgical removal of atheromas or clots (endarterectomy) in an internal carotid artery may be done. Carotid endarterectomy can help if all of the following are present:
*
The stroke resulted from narrowing of a carotid artery by more than 70%.
*
Some brain tissue supplied by the affected artery still functions after the stroke.
*
The person's life expectancy is at least 5 years.
In such people, carotid endarterectomy may reduce the risk of subsequent strokes. It also reestablishes the blood supply to the affected area, but it cannot restore lost function because some brain tissue is dead.
For carotid endarterectomy, a general anesthetic or a local anesthetic (to numb the neck area) may be used. If people remain awake during the operation, the surgeon can better evaluate how the brain is functioning. The surgeon makes an incision in the neck over the area of the artery that contains the blockage and an incision in the artery. The blockage is removed, and the incisions are closed. For a few days afterwards, the neck may hurt, and swallowing may be difficult. Most people can stay in the hospital 1 or 2 days. Heavy lifting should be avoided for about 3 weeks. After several weeks, people can resume their usual activities.
Carotid endarterectomy can trigger a stroke because the operation may dislodge clots or other material that can then travel through the bloodstream and block an artery. However, after the operation, the risk of stroke is lower for several years than it is when drugs are used.
In other narrowed arteries, such as the vertebral arteries, endarterectomy may not be possible because the operation is riskier to perform in these arteries than in the internal carotid arteries.
People should find a surgeon who is experienced doing this operation and who has a low rate of serious complications (such as heart attack, stroke, and death) after the operation. If people cannot find such a surgeon, the risks of endarterectomy outweigh its expected benefits.
Stents: If endarterectomy is too risky, a less invasive procedure can be done: A wire mesh tube (stent) with an umbrella filter may be placed in the carotid artery. The stent helps keep the artery open, and the filter catches blood clots and prevents them from reaching the brain and causing a stroke. The filter is similar to one used to prevent pulmonary embolism (see Venous Disorders: Umbrellas: One Way to Prevent Pulmonary EmbolismFigures). After a local anesthetic is given, a catheter is inserted through a small incision into a large artery near the groin or in the arm and is threaded to the internal carotid artery in the neck. A dye that can be seen on x-rays (radiopaque dye) is injected, and x-rays are taken so that the narrowed area can be located. After the stent and filter are placed, the catheter is removed. People remain awake for the procedure, which usually takes 1 to 2 hours. The procedure appears to be as safe as endarterectomy and is almost as effective in preventing strokes and death.
Other Treatments: Another option being studied is a tiny corkscrew-shaped device that is attached to a catheter, threaded to the clot, and used to snag the clot. The clot is then drawn out through the catheter. This treatment may be useful for people who cannot be given tPA.
Treatment of Problems Due to Strokes: Measures to prevent aspiration pneumonia (see Pneumonia: Aspiration Pneumonia) and pressure sores (see Pressure Sores: Prevention) are started early. Heparin, injected under the skin, may be given to help prevent deep vein thrombosis (see Venous Disorders: Deep Vein Thrombosis (DVT)). People are closely monitored to determine whether the esophagus, bladder, and intestines are functioning. Often, other disorders such as heart failure, abnormal heart rhythms, and lung infections must be treated. High blood pressure is often treated after the stroke has been stabilized.
Because a stroke often causes mood changes, especially depression, family members or friends should inform the doctor if the person seems depressed. Depression can be treated with drug therapy and psychotherapy (see Mood Disorders: Prognosis and Treatment).
Last full review/revision November 2007 by Elias A. Giraldo, MD
Tidak ada komentar:
Posting Komentar