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.

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 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).

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 narrowed 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 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 atheromas are surgically removed from the neck (carotid endarterectomy 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 ) and 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 endovascular procedures (such as 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 or placement of a stent).

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 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 has no benefit.

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 up to 6 hours (occasionally, up to 24 hours) after a stroke due to a blockage in a large artery began, they may be given tPA, with or without additional invasive treatment. In these situations, a drug or device must be inserted through a catheter and placed directly in the blocked artery. For this treatment (called thrombectomy), 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 wire on the catheter and may be injected with tPA. This treatment is usually available only at specialized stroke centers.

For mechanical thrombectomy, doctors use a device to physically remove the blood clot. This procedure is often done when people have had a severe stroke and have been ineffectively treated with tPA, given intravenously or by catheter. New evidence suggests that mechanical thrombectomy can effectively treat people who have a stroke, regardless of its severity.

Mechanical thrombectomy is usually done within 6 hours of when symptoms began. 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 MRI (perfusion MRI 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 drug cannot be used, most people are given aspirin (an antiplatelet drug) as soon as they get to the hospital. Antiplatelet drugs 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.)

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 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.

Long-term treatment of stroke usually consists of aspirin or another antiplatelet drug to reduce the risk of blood clots and thus of subsequent strokes. Clopidogrel (another antiplatelet drug) is used instead of aspirin if people are allergic to aspirin. People who have had a minor stroke may be given clopidogrel plus aspirin. This combination, given within 24 hours of when symptoms began, may be more effective than aspirin alone for reducing the risk of stroke, but only during the first 3 months after the stroke. After that, the combination has no advantage over taking aspirin alone. Also, taking clopidogrel plus aspirin increases the risk of bleeding by a small amount.

People who have atrial fibrillation or a heart valve disorder are given anticoagulants (such as warfarin) 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 and an anticoagulant.

Dabigatran, apixaban, and rivaroxaban are new anticoagulants that are sometimes 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 determine how long it takes blood to clot. Also, they are not affected by foods and are unlikely to interact with other drugs. 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 drugs for the drugs to be effective, and these drugs are significantly more expensive than warfarin.

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 Supplying the Brain With Blood Supplying the Brain With Blood ). 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 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 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 drugs 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.

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 can be done. A catheter may be used to place a wire mesh tube (stent) with an umbrella filter at its tip in the partly blocked carotid 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. The filter is removed once the stent is in place.

After a local anesthetic is given, the 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 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. After the stent is placed, the filter and catheter are removed. People remain awake for the procedure, which usually takes 1 to 2 hours.

Placement of a stent appears to be as safe as endarterectomy and as effective in preventing strokes and death.

A similar procedure can be done for other types of large blocked arteries (see figure Understanding Percutaneous Coronary Intervention (PCI) Understanding Percutaneous Coronary Intervention (PCI) ).

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 drugs 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. Sometimes an anticoagulant pill 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 lipids (cholesterol, triglycerides, or both) or a low high-density lipoprotein (HDL) cholesterol level. Lifestyle, genetics, disorders (such as low thyroid hormone... read more (such as atorvastatin) are drugs 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 drugs (such as aspirin or clopidogrel), taken by mouth may be used to prevent strokes due to atherosclerosis. These drugs include aspirin, a combination tablet of low-dose aspirin plus dipyridamole, clopidogrel, or clopidogrel plus aspirin. 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 drugs are not given to people who are taking warfarin because antiplatelet drugs 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. Dabigatran, apixaban, and rivaroxaban are newer anticoagulants that are sometimes 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 blood to clot. Also, they are not affected by foods and are unlikely to interact with other drugs. 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 drugs for the drugs to be effective. Also, these drugs are significantly more expensive than warfarin.

If other disorders such as heart failure, abnormal heart rhythms, and lung infections are present, they must be treated.

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 antidepressants Drug therapy for depression A short discussion of prolonged grief disorder. 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... read more and psychotherapy Psychotherapy A short discussion of prolonged grief disorder. 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... read more .