Causes of Ischemic Stroke

Epidemiology of ischemic stroke

Isolate primary (development in this patient for the first time in life) and secondary (development of a patient who had previously suffered an ischemic stroke) cases of stroke. There is also a fatal and nonfatal ischemic stroke. As a time interval for such assessments, an acute period of a stroke has now been taken - 28 days after the onset of neurologic symptoms (previously 21 days). Repeated worsening and death in the specified period of time is considered as a primary case and a fatal ischemic stroke. If the patient has experienced an acute period (more than 28 days), the stroke is considered as non-fatal, and with the new development of ischemic stroke the latter is defined as repeated.

Cerebrovascular diseases all over the world rank second among all causes of death and are the main cause of disability of the adult population. According to WHO, in 2002 around 5.5 million people died of stroke in the world.

The incidence of stroke varies significantly in different regions - from 1 to 5 cases per 1000 population per year. A low incidence is noted in the countries of Northern and Central Europe (0.38-0.47 per 1000 population), high in Eastern Europe. The incidence of stroke among people over 25 years of age was 3.48 ± 0.21, mortality from stroke - 1.17 ± 0.06 per 1000 population per year. In the United States, the incidence of stroke among Caucasians is 1.38-1.67 per 1000 population.

Over the past decade, in many countries in Western Europe, incidence and mortality due to stroke have decreased, but it is expected that the number of patients with stroke will increase as a result of population aging and insufficient control over the main risk factors.

Studies conducted in Europe show a clear link between the quality of the organization and the provision of medical care to patients with stroke and mortality and disability rates.

The share of acute disorders of cerebral circulation in the structure of total mortality is 21.4%. Mortality from stroke among people of working age has increased over the past 10 years by more than 30% (41 per 100 000 population). The early 30-day mortality after a stroke is 34.6%, and during the year approximately 50% of patients die, that is, every second sick person.

Stroke is the predominant cause of disability of the population (3.2 per 1000 population). According to stroke studies, 31% of stroke patients need outside help to care for themselves, 20% can not walk on their own. Only 8% of surviving patients can return to their previous work.

The National Stroke Register (2001-2005) showed that the death rate from stroke is significantly correlated with the incidence (r = 0.85, p <0.00001), but if the incidence of stroke among the regions of the country varies by a factor of 5.3, in mortality are 20.5 times. This indicates different quality of medical care in different regions, which is confirmed by differences in hospital mortality rates between regions more than 6 times.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]

Causes of Ischemic Stroke

Due to the fact that ischemic stroke is not considered as a separate disease, it is impossible for him to determine a single etiologic factor.

Allocate risk factors associated with an increased incidence of ischemic stroke. They can be divided into non-modifiable (age, sex, hereditary predisposition) and modifiable (arterial hypertension of any origin, heart disease, atrial fibrillation, history of myocardial infarction, dyslipoproteinemia, diabetes mellitus, asymptomatic carotid artery disease).

There are also risk factors associated with lifestyle: smoking, overweight, low level of physical activity, malnutrition (in particular, insufficient intake of fruits and vegetables, alcohol abuse), prolonged psychoemotional stress or acute stress.

[17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]

Pathogenesis of ischemic stroke

Acute focal brain ischemia causes a certain sequence of molecular biochemical changes in the brain substance that can lead to tissue disorders, resulting in cell death (cerebral infarction). The nature of the changes depends on the magnitude of the decrease in cerebral blood flow, the duration of this decrease, and also on the sensitivity of brain substance to ischemia.

Normally cerebral blood flow is 50-55 ml of blood per 100 g of brain substance per minute. Moderate reduction in blood flow is accompanied by selective gene expression and a decrease in protein synthesis processes. A more pronounced decrease in blood flow (up to 30 ml per 100 g / min) is accompanied by activation of anaerobic glycolysis and development of lactic acidosis.

With a decrease in cerebral blood flow to 20 ml per 100 g / min, glutamate excitotoxicity develops and the content of intracellular calcium increases, which triggers mechanisms of structural damage to membranes and other intracellular formations.

With a significant ischemia (up to 10 ml per 100 g / min), anoxic depolarization of membranes occurs, cell death usually occurs within 6-8 minutes.

In addition to cell necrosis in the focus of ischemic lesion, cell death occurs according to the type of apoptosis, for the realization of which there are certain cellular mechanisms that include several levels of intracellular regulation (they are being actively studied now).

With a moderate decrease in cerebral blood flow, an increase in the degree of oxygen extraction from the arterial blood is noted, and therefore the usual level of oxygen consumption in the brain substance can be maintained, despite the reduction in cerebral perfusion detected by the methods of neuroimaging. It should also be noted that the reduction of cerebral blood flow may be secondary and reflect the reduced need of brain cells for energy at a primary decrease in their activity, in particular, with certain pharmacological and toxic effects on the brain.

The degree of reduction of cerebral blood flow and its duration in combination with factors affecting the sensitivity of the brain to hypoxic damage determine the degree of reversibility of tissue changes at each stage of the pathological process. The zone of irreversible damage is called the heart of the infarct, the area of ischemic lesion of reversible character is designated by the term "penumbra" (ischemic penumbra). An important point is the time of existence of the penumbra, since with the passage of time reversible changes become irreversible, that is, the corresponding parts of the penumbra become the nucleus of the infarction.

There may also be an area of oligemia, it maintains a balance between tissue needs and the processes that support these needs, despite the decline in cerebral blood flow. This zone is not referred to as penumbra, since it can exist indefinitely for a long time without passing into the nucleus of the infarction.