There are two major types of stroke: hemorrhagic and ischemic. A hemorrhagic stroke refers to bleeding occurring in the brain or in the space surrounding the brain (subarachnoid hemorrhage). Although bleeding in other spaces surrounding the brain may occur (subdural, epidural), this is usually not considered a stroke. An ischemic stroke occurs when there is occlusion of a blood vessel, resulting in lack of blood supply to an area of the brain and death of brain tissue (infarction). These two types of stroke, hemorrhagic and ischemic, have different possible mechanisms.
High Blood Pressure (Hypertension)
Hypertension is very common. It has been estimated that 30% of the US population has hypertension. However, only about 60% of hypertensive individuals are aware of having hypertension. In addition, effective control of hypertension is achieved only in about one third of hypertensive individuals.
After an acute ischemic stroke occurs, physicians may allow higher than normal blood pressure, because rapid normalization of blood pressure may impair blood flow to the brain in certain circumstances. However, for most patients the long term goal is to maintain blood pressure in the normal range (<135 / 85 mm Hg). Different medications are available to treat hypertension; the choice of medication depends on the specific circumstances of each patient. Patients should discuss with their physicians any questions regarding the choice of agent, potential adverse effects, and should understand how the medications are taken.
If effective treatment is achieved, prior studies suggest that the relative risk of stroke may be decreased by 40%. It is important to note that patients should not discontinue blood pressure medications without prior discussion and agreement with their treating physicians.
High Blood Glucose (Diabetes)
Diabetes is also common, affecting 9.6% of individuals older than 20 years and 21% of those older than 60 years in the United States Patients with diabetes have a higher risk of stroke, ranging from 1.8 to 6.0, and diabetics tend to have strokes at a younger age. Impaired glucose tolerance ("pre-diabetes") doubles the risk of stroke in patients with a history of TIA or stroke.
Although there are no studies to support that tight glucose control prevents stroke, it is known that good glucose control prevents disease in small vessels in several organs including kidneys, eyes, brain and heart, and is encouraged for every patient.
Atrial fibrillation (AF) is an arrhythmia where the heart beats irregularly, and it has been associated with formation of clots (thrombi) inside the heart. Clots may travel to different areas of the body (embolization) causing infarcts, including the brain (ischemic stroke). The risk of stroke may be estimated using different models. One of them, the FSRP, is available online: http://www.framinghamheartstudy.org/risk-functions/stroke/index.php.
AF increases the risk of stroke from 2.6 to 4.5 fold depending on age. AF increases with age, and strokes due to AF have high mortality and disability rates. Anticoagulation with warfarin (coumadin) is the treatment of choice to prevent strokes in patients with AF who have associated vascular risk factors, unless there are absolute contraindications for this therapy. Adjusted-dose warfarin maintaining an INR between 2.0 and 3.0 reduces the risk of stroke by 68%. However, treatment with warfarin carries a risk of major hemorrhage, especially when the INR is above 3.0, thus requiring careful monitoring.
Despite its proven benefit, anticoagulation for stroke prevention is underutilized in patients with AF. Prior studies suggest that only 20 to 58% of patients eligible for anticoagulation actually receive it. This should be discussed in the care of patients with stroke related to AF.
High cholesterol is a risk factor for cardiovascular disease. The relation is less clear in the case of stroke, but several large studies have shown benefits from using cholesterol lowering medications. The risk of stroke is decreased by using these medications, in addition to a decrease in the risk of death and myocardial infarction. The medication and the dose used may vary for different patients, but studies have shown that the benefits are consistent.
At present, the use of statins is recommended for secondary prevention of stroke, targeting LDL cholesterol levels < 100 mg/dL in patients with high risk and < 70 mg/dL for those at very high risk.
In the United States, approximately 25% of adults are affected by cigarette smoking. Smoking increases the risk of stroke. The greater the number of cigarettes smoked per day, the higher the risk of stroke. In addition, passive smoking ("second-hand smoking") has also been related to increased stroke risk.
Smoking cessation is an effective measure to reduce stroke risk. At present there are several options to assist patients in smoking cessation. The effectiveness of smoking cessation measures has been demonstrated in prior studies. Patients should discuss with their care providers strategies for smoking cessation. Smoking cessation is recommended for all patients with stroke or TIA.
The risk of ischemic stroke also increases approximately three times for obese individuals. Obesity is also very common in the United States, with a prevalence of about 30%. Weight reduction is indicated for stroke prevention, mainly because it favorably impacts other risk factors, such as hypertension, diabetes and lipid levels.
A diet with a high content of potassium, vegetables, and fruits, low fat dairy products, low content of saturated fat and sodium is suggested as beneficial for reducing blood pressure and therefore reduce stroke risk.
Physical Activity and Stroke Prevention
A sedentary lifestyle is associated with an increased risk of stroke, and it does complicate recovery in patients who have suffered the stroke. Multiple epidemiological studies have revealed that regular physical activity is associated with a lower risk of subsequent cardiovascular and cerebrovascular events (heart attacks and both ischemic and hemorrhagic stroke). Although the precise mechanisms underlying this association are uncertain, exercise improves control of other risk factors (high blood pressure, abnormal blood lipid levels, and diabetes). The American Heart Association recommends regular physical activity to eliminate some of the risk factors for stroke. Specifically, regular moderate physical activity (jogging, hiking, running, biking, brisk walking) can reduce high blood pressure, increase "good" cholesterol, and help to loose weight and lower the risk of diabetes.
Guidelines by the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health recommend moderate exercise for 30 minutes on most, and preferably all, days of the week. In the case of stroke prevention, the benefits are apparent even for light to moderate activities, such as walking and gardening, and the data support additional benefit from increasing the level and duration of such an activity.
Further, for patient who already suffered stroke or TIA, and those able to engage in exercise programs, current recommendations are at least 30 minutes of moderate-intensity physical exercise on most days for reduction of the risk factors for stroke and the likelihood of recurrence of stroke. Also, individuals with disability after stroke could benefit from a supervised therapeutic exercise regimen in specialized settings (rehab facilities or outpatient physical therapies). Prior to beginning an exercise program, patients should discuss with their care providers the need for further evaluation and appropriate exercise programs are suitable for them. The federal government has formed a Physical Activity Guideline for Americans.
Influence of Non-Modifiable Risk Factors on Stroke
Prior studies have shown that several aspects of stroke differ between ethnic and racial groups, including features such as the severity of the stroke, and the underlying cause. In the US, Blacks, Hispanics and Native Americans have a higher incidence of stroke. In addition strokes are more severe and have higher mortality rates compared to whites. The age-adjusted incidence rates for first-ever stroke varies according to ethnicity, and has been reported to be 167, 138, 323, and 260 per 100,000 population among white men, white women, black men and black women respectively.
The specific treatment may be influenced by ethnicity because response to some medications may vary among different ethnic groups. Assessment of vascular risk factors is done equally for all patients regardless of their ethnicity.