What is a stroke?
A stroke is a failure of blood flow that affects a large or small area of the brain. It occurs as a result of a blockage or rupture of a blood vessel and causes the death of nerve cells, which are deprived of oxygen and nutrients essential to their functions. In most people, there are no warning signs of a seizure. However, there are several risk factors that can be monitored.
The consequences of stroke vary widely. More than half of the people who have a stroke have some after-effects. About 1 in 10 people recover completely.
The severity of the damage depends on the area of the brain affected and the functions it controls. The larger the area deprived of oxygen, the more severe the damage is likely to be. Following a stroke, some people will have difficulty speaking or writing (aphasia) and memory problems. They may also experience varying degrees of paralysis.
Signs of stroke, a medical emergency
When nerve cells are deprived of oxygen for even a few minutes, they die; they will not regenerate. The shorter the time between the stroke and medical attention, the lower the risk of serious consequences.
Regardless of the damage caused by oxygen deprivation, the brain has some ability to adapt. Healthy nerve cells can sometimes take over from dead cells if stimulated by various exercises.
Atherosclerosis, the formation of fatty plaques on the walls of blood vessels, is one of the main causes of stroke. High blood pressure is also a major risk factor. Over time, the abnormal pressure exerted by blood on the walls of blood vessels can cause them to rupture. The rupture of an artery in the brain can be facilitated by the presence of an aneurysm. An aneurysm is a swelling of a small section of an artery due to a weakness in the wall.
It is not always possible to determine the exact cause of a stroke. It is important, however, that doctors look for it through various tests to reduce the risk of recurrence.
Thanks to advances in prevention, the prevalence of stroke has decreased significantly over the past few decades. Since the 1990s, however, the prevalence of stroke appears to have stabilized.
Even today, more than 50,000 people in Canada have a stroke each year and about 14,000 die from it. Although strokes are rarer than heart attacks, they are still the third leading cause of death in Canada and a major cause of disability.
Three quarters of strokes occur in people aged 65 and over. In Canada and North America, they generally affect women more than men. Young children can also suffer from stroke, but this is rare.
Types of Stroke
There are 3 types of stroke: the first 2 are caused by blockage of a cerebral artery ( ischemic attack ). They are the most common and represent about 80% of strokes. The third is caused by a brain hemorrhage ( hemorrhagic accident ):
- Cerebral thrombosis. It represents 40% to 50% of cases. It occurs when a blood clot forms in a cerebral artery on a plaque of lipids (atherosclerosis);
- Cerebral embolism. It represents about 30% of cases. As with thrombosis, a cerebral artery is blocked. However, here the clot that is blocking the artery has formed elsewhere and has been carried by the bloodstream. It often originates from the heart or a carotid artery (in the neck);
- Cerebral hemorrhage. It accounts for about 20% of cases, but it is the most serious form of stroke. Often caused by long-standing hypertension, it can also result from a ruptured artery in the brain, where an aneurysm is located .
In addition to depriving part of the brain of oxygen, the bleeding destroys other cells by putting pressure on the tissues. It can occur in the center or the periphery of the brain, just below the cranial envelope.
Other, more rare, causes of brain hemorrhages include hypertensive attacks, hemorrhage into a brain tumor, and blood clotting problems.
Sometimes a cerebral artery blockage is only temporary and resolves naturally, leaving no after-effects. This phenomenon is called transient ischemic attack (TIA) or mini-stroke. The diagnosis is confirmed by an MRI. The symptoms are the same as those of a “real” stroke, but they disappear within an hour. A mini-stroke is a warning sign to be taken seriously: it can be followed by a stroke, sometimes more serious, in the next 48 hours. It is therefore important to see a doctor as soon as possible.
Signs of Stroke
A stroke can cause paralysis or loss of consciousness. Sometimes it can be detected by any of the following signs:
- Dizziness and sudden loss of balance;
- sudden numbness, loss of feeling or paralysis of the face, arm, leg or side of the body
- confusion, sudden difficulty in speaking or understanding
- sudden loss of vision or blurred vision in one eye
- a sudden, severe headache, sometimes accompanied by vomiting.
- In all cases, emergency services should be contacted as soon as possible.
People at risk of stroke
- People who have already had a transient ischemic attack (mini-stroke) or a stroke;
- People with a heart condition (heart valve defect, heart failure or heart arrhythmia) and those who have recently had a heart attack. Atrial fibrillation, a form of cardiac arrhythmia, is particularly dangerous because it causes blood to stagnate in the heart, leading to the formation of blood clots. If these clots travel to the arteries in the brain, they can cause a stroke;
- People with diabetes. Diabetes contributes to atherosclerosis and reduces the body’s ability to dissolve blood clots;
- People who suffer from migraines;
- People with sleep apnea. Sleep apnea can cause blood pressure to rise and contribute to blood clots;
- People with a high number of red blood cells in the blood (polycythemia);
- People who have a close relative who has had a stroke.
Risk factors for stroke
The two main factors
- High blood pressure. This is the most important risk factor. High blood pressure weakens the lining of blood vessels, including those in the brain;
- High cholesterol. High levels of LDL cholesterol (low density lipoproteins) or triglycerides contribute to atherosclerosis and hardening of the arteries.
- Smoking. It contributes to atherosclerosis. Moreover, nicotine acts as a cardiac stimulant and increases blood pressure. Carbon monoxide in cigarette smoke reduces the amount of oxygen reaching the brain because it binds to red blood cells instead of oxygen;
- Poor diet;
- A sedentary lifestyle;
- Chronic stress;
- Excessive use of alcohol or hard drugs, such as cocaine;
- Taking oral contraceptives, especially for women who are at risk and over 35 years old;
- Hormone replacement therapy given at the time of menopause (slightly increases the risk).
Note. These factors also increase the risk of developing coronary heart disease. See our Heart Disorders fact sheet.
Can you prevent it?
According to the American Heart Association’s 2011 Stroke Prevention Guide, people with healthy lifestyle habits reduce their risk of having a first stroke by 80% compared with those who neglect risk factors.1
Basic preventive measures
- Adopt healthy lifestyle habits
- Do not smoke;
- Avoid excessive alcohol consumption;
- Find ways to incorporate physical activity into your daily life;
- Maintain a healthy weight. To calculate your body mass index (BMI), take our test;
- Make good food choices: diet influences many risk factors for stroke.
- Researchers reviewed 375 studies published between 1979 and 2004 to determine what type of diet best helps prevent stroke3. They found that a diet low in salt (less than 1150 mg per day) and high in potassium and magnesium lowers blood pressure and thus helps prevent stroke. A diet rich in fruits and vegetables generally provides adequate amounts of potassium. Whole grains, nuts, seeds, legumes and dark green leafy vegetables are good sources of potassium. Studies show that people who eat about 10 servings of fruits and vegetables a day, who choose whole grains and who eat 1 to 2 servings of fatty fish a week are less likely to have a stroke.
- In terms of diet, the Dietary Approaches to Stop Hypertension (DASH) and the Mediterranean diet have been shown to be effective in preventing hypertension3. For more information on the DASH diet, see the Hypertension fact sheet;
- Learn to cope better with stress;
- Change your birth control method if necessary. Women over 35 who are on birth control pills and are considered at risk (because they smoke or have high blood pressure…) should switch to another birth control method, such as an intrauterine device or a progesterone-only pill.
Measures to prevent recurrence
Take anticoagulant medication. People who have already had a transient ischemic attack (mini-stroke), or a stroke caused by thrombosis or embolism, are advised to take a daily medication to reduce the risk of a blood clot forming. This may be an anticoagulant such as warfarin (Coumadin®) or dabigatran (Pradax®), or an antiplatelet medication such as aspirin or dipyridamole (Aggrenox®). People for whom aspirin is contraindicated can take clopidogrel bisulfate (Plavix®) or ticlopidine hydrochloride (Ticlid®).
Medical treatments for stroke
Important. A stroke is a medical emergency and requires immediate treatment, just like a heart attack. Emergency services should be contacted as soon as possible, even if the symptoms resolve after a few minutes. The sooner care is obtained, the less likely it is that any after-effects will remain.
The first goal is to minimize damage to the brain by restoring blood flow in the case of an ischemic stroke diagnosed by MRI or by reducing blood loss in the case of a hemorrhagic stroke. If the stroke is severe, the person will remain in hospital for observation for a few days. A period of rehabilitation, either at home or in a specialized center, may be required. In addition, the cause of the stroke must be investigated and treated (for example, by correcting high blood pressure or heart arrhythmia).
If an artery is blocked
Only one drug is approved to reduce the risk of irreversible brain damage. It is indicated for strokes caused by thrombosis or embolism. It is a tissue plasminogen activator, a blood protein that helps dissolve clots quickly (within an hour or two). To be effective, the drug must be injected intravenously within 3 to 4.5 hours of the stroke, which greatly limits its use.
A few hours after a non-hemorrhagic stroke, an anticoagulant or antiplatelet medication is often given. This medication helps prevent new blood clots from forming in the arteries. It also prevents the growth of clots that have already formed. Once the stroke is stabilized, the doctor usually suggests a milder medication, such as aspirin, to be taken daily over the long term.
During the rehabilitation period, other medications may be helpful. For example, antispasmodic medications can help relieve muscle spasms.
If there is a bleed
In the hours following this type of stroke, blood pressure lowering medications are usually given to limit bleeding and the risk of rebleeding. Sometimes the hemorrhage can trigger epileptic seizures. In this case, they will be treated with drugs from the benzodiazepine class.
If an artery is blocked
Once the stroke has stabilized, the doctor offers various tests to find out if other arteries are weakened by atherosclerosis . He may offer one of the following preventive surgeries:
- carotid endarterectomy. This intervention consists of “cleaning” the wall of the carotid artery affected by atherosclerosis. It has been practiced for forty years and is intended to prevent the recurrence of strokes;
- an angioplasty. A balloon is placed in the artery affected by atherosclerosis to prevent its blockage. A small metal rod is also inserted into the artery to prevent it from narrowing. This procedure carries more risk than the previous one, because when the atherosclerotic plaque is crushed by the balloon, fragments of the plaque may be released and cause another blockage further in the cerebral artery.
If there is a hemorrhage
Brain surgery may be necessary to remove the accumulated blood. If the surgeon finds an aneurysm at the time of surgery, they treat it to prevent it from rupturing and another stroke. Treatment most often involves placing a platinum filament in the aneurysm. A blood clot will then form around it and fill the dilation of the blood vessel.
Remark. Occasionally, a medical examination may reveal the presence of an unruptured aneurysm in the brain. Depending on the context, the doctor may or may not recommend preventive surgery. If the patient is under 55, the doctor will usually suggest this preventive surgery. If the patient is older, a choice must be made taking into account the benefits and risks of the operation. Indeed, the latter exposes the patient to a risk of neurological sequelae ranging from 1% to 2%, and to a risk of mortality of approximately 1% 2 . In addition, more studies are needed to know the real effect of such an intervention on stroke prevention.