Stroke

Stroke is a vascular disease that affects the territory supplied by the carotid artery. The majority of strokes (88%) are ischaemic, that is, the result of an interruption in blood flow to the brain. This can be caused by the development of atherosclerosis. There are three types of ischaemic stroke: thrombotic infarct, embolic infarct, and lacunar infarct. Haemorrhagic strokes occur less frequently and result from a ruptured blood vessel, leading to bleeding or haemorrhage. Haemorrhagic stroke can be caused by an aneurysm or by an arteriovenous malformation. A transient ischaemic attack (TIA) – often known as a mini-stroke – occurs when blood supply to the brain is interrupted for a short periods of time (from a few minutes to 24 hours). Although this can be resolved by normal treatment, the risk of subsequent stroke within the following 48 hours is high.

Incidence of stroke and impact

Stroke is the third leading cause of death in most developed countries and is also a major cause of morbidity, long-term disability and hospital admission. It represents amajor health problem worldwide, affecting over 20 million people each year. Stroke is associated with a 25% mortality rate, representing approximately 5 million deaths worldwide each year. High blood pressure is estimated to contribute to over 12.7 million strokes worldwide. Substantial variability exists in both incidence and mortality from stroke in Europe, with high numbers in Eastern European countries and low numbers in Northern and Middle European Countries. Although 75% of strokes are non-fatal, stroke has a significant impact on society because >33% of stroke patients will suffer from a disability which causes them to become dependent on others for everyday activities. Among those who survive a first stroke, the risk of recurrence is very high, being greatest in the first year after the initial event while at least one in six patients suffer another stroke within 5 years. These data highlight the importance of studying the causes, treatment, prevention and aftercare of strokes.

Risk factors for stroke

There are a number of independent risk factors associated with stroke. These factors can be classified as either non-modifiable or modifiable. Inherent biological traits, such as age and gender, cannot themselves be altered: risk of stroke increases with age and occurs more frequently in males. Social characteristics, such as social class and ethnic group, also show pronounced differences in rate of stroke occurrence. For example, rates are as high in Afro-Caribbeans in the UK, and high in blacks in the USA. Patients with a history of TIA are at substantial risk for subsequent stroke, particularly within the first few days. Other uncontrollable risk factors include a history of stroke or previous myocardial infarction (MI). Depending on the way in which they can be modified, risk factors can be divided into two groups: lifestyle changes and pharmacotherapy. Certain lifestyle changes can reduce the risk of stroke. These include smoking cessation, increasing physical activity, weight reduction, reducing alcohol consumption, and having less salt and fat in the diet. These changes reduce the risk not only of stroke, but also of cardiovascular diseases in general, including hypertension and heart disease. Pharmacotherapy for existing diseases can also reduce the likelihood of stroke. Patients with arterial disease, atherosclerosis or heart failure, or certain blood disorders, are at a greater risk of stroke owing to the increased likelihood of thrombosis and embolism. Anticoagulants and anti-platelet agents can be used to reduce the risk of thrombosis. High blood cholesterol is a major risk factor for heart disease, which increases the risk of stroke. Statins can be used to reduce blood cholesterol and have been associated with a significant reduction in the risk of stroke. Patients with diabetes are also at increased risk of stroke, even if their blood glucose levels are controlled. These patients tend in addition to have hypertension, high blood cholesterol, and are often overweight. Effective management of all of these conditions can reduce the risk of stroke.

Hypertension as a risk factor for stroke

Hypertension is the single most important controllable stroke risk factor. Successful long term treatment of hypertension can reduce the risk of stroke by as much as 33%. It is well-established that the risk of stroke rises almost linearly with increasing SBP and DBP in all age groups. Studies involving more than 400,000 patients have assessed the link between blood pressure and primary incidence of stroke. The results from the Framingham Heart Study confirmed that high blood pressure is indeed a major risk factor for primary stroke. Evidence from the Hypertension Optimal Treatment (HOT) study suggests the lowest risk of stroke is achieved at a SBP of 140–145 mm Hg and a DBP of ،ـ80 mm Hg.

Primary stroke prevention through blood pressure control

Primary prevention of stroke includes lifestyle modifications (weight loss, alcohol restriction, regular aerobic physical activity, and smoking cessation), and measures to control blood pressure, cholesterol levels, diabetes mellitus, and atrial fibrillation. Control of blood pressure is the most effective method for the primary prevention of stroke. The benefit of antihypertensive treatment in the primary prevention of stroke has been proven in many trials: effective lowering of blood pressure reduces fatal and non-fatal stroke by approximately 40% within 2–3 years.

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