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Stroke: Causes and Prevention

Introduction

A stroke is a sudden injury to the brain caused by an abnormality in a brain blood vessel. It is manifested as a neurologic symptom or loss of function, such as severe headache, weakness, loss of sensation or balance, confusion, or inability to speak. Strokes come in two major varieties: hemorrhagic strokes, which are caused by bleeding into the brain, and ischemic strokes, which are caused by blockage of blood flow to the brain.

Hemorrhagic strokes occur when blood from a ruptured blood vessel compresses and damages normal functioning brain tissue. This rupture may occur because of underlying damage to the blood vessel from years of high blood pressure or from an underlying abnormality in a blood vessel, such as an aneurysm (abnormal bulging of a blood vessel). High blood pressure is the most important risk factor for a hemorrhagic stroke, but other possible causes include alcohol abuse, drug abuse (especially cocaine), and cigarette smoking.

Most strokes, about 80 percent, are ischemic strokes. In an ischemic stroke, a blocked artery prevents blood carrying oxygen and other nutrients from reaching a portion of the brain, leading to dysfunction and death of that brain tissue. What happens during an ischemic stroke is in many ways similar to what happens in a heart attack in which there is a blockage of blood flow to the heart. Because of this similarity, strokes and heart disease share many risk factors, but there are important differences as well. While controlling risk factors for heart disease (specifically, coronary artery disease), will also have the added benefit of prevention of stroke, there are additional ways in which one can reduce the risk of having a stroke. The major risk factors for both heart disease and ischemic stroke include:

• high blood pressure
• diabetes
• increased cholesterol
• cigarette smoking
• obesity
• physical inactivity

• atrial fibrillation
• carotid artery stenosis
• transient ischemic attack (TIA)
• transient monocular blindness
• migraine

The Risks and Preventive Measures

The following is a list of risk factors for stroke, and how behavior can be modified and treatment utilized to reduce the risk.

High blood pressure
High blood pressure is the most important modifiable risk factor for stroke. Several studies have shown that all forms of hypertension are associated with an increased risk of stroke, whether the elevation is in the upper number of the blood pressure (the systolic) or the lower number (the diastolic). Interestingly, there is no clear lower limit below which there is no further reduction in risk of stroke: that is, the lower the blood pressure, the less the risk of stroke, even in the so-called normal range. Many drug studies have shown that controlling blood pressure can reduce one’s chance of having a stroke.

Diabetes
Most studies have shown that, in addition to heart disease and other complications, diabetes is associated with an increased risk of stroke. Recent studies suggest that control of blood sugar in diabetes can reduce the risk of these complications, and certain medications may also reduce the risks of stroke.

High cholesterol
High cholesterol (hyperlipidemia) also may cause strokes by contributing to atherosclerosis, or hardening of the arteries. Studies have shown that controlling the level of cholesterol, especially with a family of medications called statins, may reduce the risk of strokes in people with high cholesterol or heart disease. Whether it makes sense to treat people with strokes and normal cholesterol levels to produce an even lower cholesterol level remains unanswered.

Cigarette smoking
Cigarette smoking increases the risk of stroke, and the more one smokes, the bigger the risk. Cigarette smoking also increases the chances of subarachnoid hemorrhage, the kind of bleeding stroke that occurs from a burst aneurysm. It is reassuring to know that the risk of stroke is reduced to that of a nonsmoker within two to five years after quitting.

Obesity and physical inactivity
Obesity and physical inactivity can also lead to strokes. Even moderate physical activity, such as walking, can reduce an individual’s risk.

The risk factors specific to stroke include atrial fibrillation, carotid artery stenosis, transient ischemic attack, transient monocular blindness, and migraine.

Atrial fibrillation
Atrial fibrillation refers to a certain kind of irregular heart rhythm, which leads to blood clots forming in the heart. These blood clots can then be released from the heart and travel to the brain, causing what is referred to by doctors as an embolic stroke. Blood thinners, such as warfarin, are routinely used to reduce the chances of stroke in people with this kind of arrhythmia. Atrial fibrillation is very common in elderly people (approximately 10 percent), but may occur in younger people too. In young people who have atrial fibrillation but no other risk factors for heart disease or stroke, the chances of having a stroke are so remote that blood thinners are often not used. Many other heart conditions can also cause strokes, including valvular heart disease, rheumatic heart disease, and congestive heart failure. Some of these may also need to be treated with blood thinners in certain circumstances.

Carotid artery stenosis
Carotid artery stenosis refers to a severe narrowing of the carotid arteries, the main sources of blood flow to the brain. People with this condition are at increased risk of having a stroke. A surgical procedure called a carotid endarterectomy, which is like a cleaning out of the blood vessel, can be used to reduce the risks of a stroke in such people. This procedure is usually reserved for people without severe heart disease or other medical problems, however. Only one’s doctor can tell whether a person is a good candidate for this kind of surgery.

Transient ischemic attacks
Transient ischemic attacks, or TIAs, are often called "mini-strokes." These are short-lived episodes of sudden disturbance of strength, sensation, balance, speech, or vision, which signal that a person is at increased risk of stroke. They should always be brought to a doctor’s attention, since tests may need to be performed to exclude treatable causes of stroke like those mentioned above. The failure to treat these conditions, if present, could lead to the occurrence of a full-blown, crippling stroke. One particular kind of TIA, called amaurosis fugax or transient monocular blindness, refers to the sudden loss of vision in one eye lasting a few minutes. This may signal a blockage in one of the carotid arteries.

Migraine
Migraine appears to be a risk factor for strokes as well. This is not to say that everyone who suffers from migraines is at high risk of stroke. In fact, stroke is a very rare complication of migraines. It has been hypothesized that it is the abnormal constriction of brain blood vessels during migraine that increases the risk of stroke. Some studies have suggested that people who experience an aura, such as a change in vision or loss of strength or sensation, prior to their migraine may have an especially increased risk of stroke, though it is unclear why. People with migraines who have suffered strokes should probably avoid medications that constrict blood vessels.
 

Conclusion

If you have risk factors for stroke, or if you have had a TIA or stroke, it is imperative that you tell your doctor. The prescription of certain medications, and the change of certain behaviors, as described above, can markedly reduce the chance of a first or recurrent stroke.
 

List of Risk Factors for Stroke

Nonmodifiable risk markers
Older age
Male gender
Race and ethnicity
Genetic factors

Modifiable risk factors
High blood pressure
Atrial fibrillation
Other heart diseases
High cholesterol
Cigarette smoking
Diabetes mellitus
Physical inactivity
Carotid artery stenosis
Transient ischemic attack
Migraine