Ischemic Stroke

Commonly, blockages are blood clots (thrombi) or pieces of fatty deposits (atheromas, or plaques) due to atherosclerosis Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more . Such blockages often occur in the following ways:

Blood clots in a brain artery do not always cause a stroke. If the clot breaks up spontaneously within less than 15 to 30 minutes, brain cells do not die and people's symptoms resolve. Such events are called transient ischemic attacks Transient Ischemic Attacks (TIAs) A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply. The cause and symptoms... read more (TIAs).

If an artery narrows very gradually, other arteries (called collateral arteries—see figure Supplying the Brain With Blood Supplying the Brain With Blood ) sometimes enlarge to supply blood to the parts of the brain normally supplied by the clogged artery. Thus, if a clot occurs in an artery that has developed collateral arteries, people may not have symptoms.

The most common causes of ischemic stroke can be classified as

Stroke is classified as cryptogenic when no clear cause is identified despite a complete evaluation.

Blood clots can form in the heart, especially in people who have or have had the following:

Tiny pieces of these blood clots can break off and travel to small arteries in the brain (as emboli).

Lacunar infarction refers to tiny ischemic strokes, typically no larger than about a third of an inch (1 centimeter). In lacunar infarction, one of the small arteries deep in the brain becomes blocked when part of its wall deteriorates and is replaced by a mixture of fat and connective tissue—a disorder called lipohyalinosis. Lipohyalinosis is different from atherosclerosis, but both disorders can cause arteries to be blocked.

Lacunar infarction can also occur when tiny pieces of fatty material that has been deposited in arteries (atheromas or atherosclerotic plaques Plaque formation Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more ) break off and travel to small arteries in the brain.

Lacunar infarction tends to occur in older people with diabetes or poorly controlled high blood pressure. Only a small part of the brain is damaged in lacunar infarction, and the prognosis is usually good. However, over time, many small lacunar infarcts may develop and cause problems, including problems with thinking and other mental functions (cognitive impairment).

In large-vessel atherosclerosis Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more , atherosclerotic plaques develop in the walls of large arteries, such as those that supply the brain (cerebral arteries).

The plaques can gradually enlarge and cause the artery to narrow. As a result, tissues supplied by the artery may not receive enough blood and oxygen. Plaques tend to split open (rupture). Then material inside the plaque is exposed to the bloodstream. The material triggers the formation of blood clots (called thromboses). These blood clots can suddenly block all blood flow through an artery. Sometimes the blood clots break off, travel through the bloodstream and block an artery that supplies blood to the brain (called emboli). Both thromboses and emboli can cause a stroke by blocking the blood supply to an area of the brain.

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. They include the following:

An ischemic stroke can also result from any disorder that reduces the amount of blood supplied to the brain. For example,

Rarely, a stroke results from a general decrease in blood flow, as occurs when people lose a lot of blood, become severely dehydrated, or have very low blood pressure. This type of stroke often occurs when arteries supplying the brain are narrowed but had not previously caused any symptoms and had not been detected.

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 Overview of Anemia Anemia is a condition in which the number of red blood cells is low. Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts... read more ), suffocation, and carbon monoxide poisoning Carbon Monoxide Poisoning Carbon monoxide is a colorless, odorless gas that is produced when many materials are burned and can be toxic when breathed in large amounts Carbon monoxide poisoning is common. Symptoms may... read more . Usually, brain damage in such cases is widespread (diffuse), and coma results.

Sometimes a blood clot in a leg vein (deep venous thrombosis Deep Vein Thrombosis (DVT) Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more ) or, rarely, small pieces of fat from the marrow of a broken leg bone move into the bloodstream. Usually, these blood clots and pieces of fat travel to the heart and block an artery in the lungs (called pulmonary embolism Pulmonary Embolism ). However, some people have an abnormal opening between the right and left upper chambers of the heart (called a patent foramen ovale). In such people, the blood clots and pieces of fat may go through the opening and thus bypass the lungs and enter the aorta (the largest artery in the body). If they travel to arteries in the brain, a stroke can result.

Some risk factors for ischemic stroke can be controlled or modified to some extent—for example, by treating the disorder that increases risk.

The major modifiable risk factors for ischemic stroke are

Risk factors that cannot be modified include

Strokes can lead to other problems (complications):

The losses and problems resulting from the stroke may make people depressed.

Identifying the precise cause of an ischemic stroke is important. If the blockage is a blood clot, another stroke may occur 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:

Imaging tests enable doctors to determine how narrowed the carotid arteries are and thus to estimate the risk of a subsequent stroke or transient ischemic attack Transient Ischemic Attacks (TIAs) A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply. The cause and symptoms... read more (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 substance that can be seen on x-rays (radiopaque contrast agent) 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. Cerebral angiography is done before any endovascular procedure that uses a catheter to treat a blocked or narrowed arteries. Cerebral angiography is also done when vasculitis Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more is suspected.

Because CT angiography is less invasive, it has largely replaced cerebral angiography done with a catheter. The exceptions are when endovascular procedures are planned. These procedures involve using instruments threaded through a catheter to physically remove a clot (mechanical thrombectomy Mechanical thrombectomy An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more ), to widen a narrowed artery (angioplasty), and/or to place a tube made of wire mesh (a stent) to keep the artery open.

In certain circumstances, a medication called tissue plasminogen activator (tPA) is given intravenously to break up clots and help restore blood flow to the brain. Two tPAs are available: alteplase and tenecteplase.

Because tPA can cause bleeding in the brain and elsewhere, it usually should not be given to people with certain conditions, such as the following:

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. Some experts recommend using tPA up to 4.5 hours after an ischemic stroke begins.

But when tPA is given between 3 and 4.5 hours, additional conditions may prohibit its use. These conditions include

After 4.5 hours, giving tPA intravenously increases the risk of bleeding.

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 some people who have had a stroke. If advanced imaging identifies undamaged brain tissue, people may be given tPA even if doctors cannot determine when the stroke began—for example, if people wake up and have had a stroke sometime during the night.

For mechanical thrombectomy, doctors use a device to physically remove the blood clot in large cerebral arteries. This procedure is often done when people have had a severe stroke. New evidence suggests that mechanical thrombectomy can effectively treat people who have a stroke, regardless of its severity.

Mechanical thrombectomy is traditionally done within 6 hours of when symptoms began. However, the procedure can be done up to 24 hours after symptoms began if imaging tests show undamaged brain tissue. Thus, at some stroke centers, doctors are starting to use a special type of CT or MRI (perfusion imaging Perfusion MRI In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more ) and other imaging tests to determine how much a stroke has progressed, rather than going strictly by time. These tests can show how much blood flow has been reduced and indicate how much brain tissue may be saved. This approach (based on brain tissue status, not time) is especially useful when doctors are unsure of when the stroke began—for example, when people wake up in the morning and have symptoms of a stroke. If imaging tests show that blood flow is only somewhat reduced, treatment with mechanical thrombectomy up to 24 hours after symptoms start may still be able to save brain tissue. But if blood flow has been greatly reduced or has stopped, treatment after only 1 hour may be unable to save any brain tissue.

Different types of devices can be used. For example, the stent retriever may be used. It resembles a tiny wire cage. It can be attached to a catheter, which is inserted through an incision, often in the groin, and threaded to the clot. The cage is opened up, then closed around the clot, which is drawn out through a larger catheter. If done within 6 hours of the stroke's start, mechanical thrombectomy with a stent retriever can dramatically improve outcomes in people with a large blockage. Devices can restore blood flow in 90 to 100% of people.

Mechanical thrombectomy is done only in stroke centers.

If a thrombolytic medication cannot be used, most people are given aspirin (an antiplatelet medication) as soon as they get to the hospital. Antiplatelet medications make platelets less likely to clump and form clots. (Platelets are tiny cell-like particles in the blood that help it clot in response to damaged blood vessels.) Taking aspirin plus clopidogrel (another antiplatelet medication) is slightly more effective than aspirin alone for reducing the risk of another stroke, but only if given within 24 hours after stroke symptoms began. It is given only for first 3 weeks after the stroke and reduces the risk of recurrence only for the first 3 months after a stroke. After that, the combination has no advantage over aspirin alone. Also, taking clopidogrel plus aspirin for more than 3 weeks increases the risk of bleeding by a small amount. However, the combination is sometimes given for 3 months in certain circumstances—for example, when people have a partial blockage of a large artery.

If symptoms seem to be worsening despite other treatments, anticoagulants such as heparin and warfarin are used. They may also be used to treat specific types of strokes (such as those due to a blood clot in a vein in the brain, or atrial fibrillation, or dissection of an artery in the neck). Anticoagulants inhibit proteins in blood that help it to clot (clotting factors).

If people have been given a thrombolytic medication, doctors usually wait at least 24 hours before antiplatelet medications or anticoagulants are started because these medications 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.

Once an ischemic stroke is completed, surgical removal of fatty deposits (atheromas, or plaques) due to atherosclerosis or clots in an internal carotid artery may be done (see figure ). This procedure, called carotid endarterectomy, can help if all of the following are present:

In such people, carotid endarterectomy may reduce the risk of subsequent strokes. This procedure 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 is used. The surgeon makes an incision in the neck over the area of the artery that contains the blockage, then 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 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 than it is when medications are used, and this risk is lower for several years. The procedure can result in a heart attack because people who have this procedure often have risk factors for coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more .

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 may outweigh its expected benefits.

If endarterectomy is too risky or cannot be done because of the artery's anatomy, a less invasive procedure (carotid artery angioplasty) can be done to widen the artery.

For this procedure, a local anesthetic is given. Then a catheter with an umbrella filter at its tip is inserted through a small incision into a large artery near the groin or in the arm, and the catheter is threaded to the internal carotid artery in the neck. A substance that can be seen on x-rays (radiopaque contrast agent) is injected, and x-rays are taken so that the narrowed area can be located. Doctors use the catheter to widen the carotid artery, then insert a tube made of wire mesh (a stent) into the artery. Once in place, the stent is expanded to help keep the artery open. The filter catches any debris that may break off during the procedure.

After the stent is placed, the catheter and the filter at its tip are removed. People remain awake for the procedure, which usually takes 1 to 2 hours.

Placement of a stent appears to be as safe and as effective in preventing strokes and death as endarterectomy Carotid artery surgery An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more . For younger people and people who do not have risk factors for heart or blood vessel disorders (such as high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more , high cholesterol levels Dyslipidemia Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more , diabetes Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , and smoking Smoking Smoking tobacco is harmful to almost every organ in the body. Smoking increases the risk of heart attack, lung cancer, chronic obstructive pulmonary disease (COPD), and other disorders. Nicotine... read more ), carotid endarterectomy is usually done.

A similar procedure can be done for other types of large blocked arteries (see figure ).

Long-term treatment of stroke includes measures to do the following:

During the recovery period, high blood sugar (hyperglycemia) and fever can make brain damage worse after a stroke. Lowering them limits the damage and results in better functioning.

Before people who have had a stroke start to eat, drink, or take medications by mouth, they are checked for problems with swallowing. Problems with swallowing can lead to aspiration pneumonia Aspiration Pneumonia and Chemical Pneumonitis Aspiration pneumonia is lung infection caused by inhaling mouth secretions, stomach contents, or both. Chemical pneumonitis is lung irritation caused by inhalation of substances irritating or... read more . Measures to prevent this problem are started early. If problems are detected, a therapist can teach people how to swallow safely. Sometimes people need to be fed through a tube (tube feeding Tube Feeding Tube feeding may be used to feed people whose digestive tract is functioning normally but who cannot eat enough to meet their nutritional needs. Such people include those with the following... read more ).

If people cannot move on their own or have difficulty moving, they are at risk of developing blood clots in their legs (deep vein thrombosis Prevention Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more ) and pressure sores Prevention Pressure sores are areas of skin damage resulting from a lack of blood flow due to prolonged pressure. Pressure sores often result from pressure combined with pulling on the skin, friction,... read more . Pneumatic compression stockings may be used to prevent blood clots. Powered by an electric pump, these stockings repeatedly squeeze the calves and move blood into and through the veins. People at high risk of developing blood clots may also be given an anticoagulant (such as heparin), injected under the skin of the abdomen or arm. Often, an anticoagulant is given by mouth.

Measures to prevent pressure sores Prevention Pressure sores are areas of skin damage resulting from a lack of blood flow due to prolonged pressure. Pressure sores often result from pressure combined with pulling on the skin, friction,... read more are started early. For example, staff members periodically change the person's position in bed to help prevent pressure sores from forming. They also regularly inspect the skin for any sign of pressure sores.

Controlling or treating risk factors for stroke (such as high blood pressure, diabetes, smoking, consumption of too much alcohol, high cholesterol levels, and obesity) can help prevent future strokes.

Statins Lipid-lowering drugs Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more (such as atorvastatin) are medications that lower levels of cholesterol and other fats (lipids). They are often given when strokes result from the buildup of fatty deposits in an artery (atherosclerosis Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more ). Such therapy can help prevent strokes from recurring.

Antiplatelet medications, taken by mouth, may be used to reduce the risk of blood clots and thus help prevent strokes due to atherosclerosis. One of the following can be used:

Clopidogrel is indicated for people who are allergic to aspirin.

Taking clopidogrel plus aspirin appears to reduce the risk of future strokes more than taking aspirin alone, but only for the first 3 months after a stroke. After that, the combination has no advantage over aspirin alone. Also, taking clopidogrel plus aspirin for a long time increases the risk of bleeding by a small amount. Usually, antiplatelet medications are not given to people who are taking warfarin because antiplatelet medications add to the risk of bleeding, but, occasionally, there are exceptions.

Anticoagulants (such as warfarin), taken by mouth, may be used to prevent strokes due to blood clots. When people are taking warfarin, blood tests are done regularly to measure how long it takes for blood to clot. Regular testing is needed to make sure the dose of warfarin is not too high. If the dose is too high, the risk of bleeding is increased.

Dabigatran, apixaban, and rivaroxaban are newer anticoagulants that are often used instead of warfarin. These newer anticoagulants are more convenient to use because they, unlike warfarin, do not require regular monitoring with blood tests to measure how long it takes for blood to clot. Also, they are not affected by foods and are unlikely to interact with other medications. But the new anticoagulants have some disadvantages. Dabigatran and apixaban must be taken twice a day (warfarin is taken once a day). Also, people must not miss any doses of the newer medications for the medications to be effective. Also, these medications are significantly more expensive than warfarin.

People who have atrial fibrillation Atrial Fibrillation and Atrial Flutter Atrial fibrillation and atrial flutter are very fast electrical discharge patterns that make the atria (upper chambers of the heart) contract very rapidly, with some of the electrical impulses... read more or a heart valve disorder Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more are given anticoagulants (such as warfarin) instead of antiplatelet medications, which do not seem to prevent blood clots from forming in the heart.

Occasionally, people at high risk of another stroke (such as people who have had a minor stroke) are given aspirin plus an anticoagulant.

If other disorders such as heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , abnormal heart rhythms, Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more and lung infections are present, they must be treated.

Because a stroke often causes mood changes, especially depression Depression Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to interfere with functioning. It may follow a recent... read more , family members or friends should inform the doctor if the person seems depressed. Depression can be treated with antidepressants Drug therapy for depression Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to interfere with functioning. It may follow a recent... read more and psychotherapy Psychotherapy Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to interfere with functioning. It may follow a recent... read more .