High blood pressure is the most powerful and frequent risk factor behind strokes (1-4), far ahead of diabetes, high cholesterol, smoking, sleep apnea syndrome, hyperhomocysteinemia and inflammatory syndrome.
In addition, the first target of hypertension is the brain, in front of the myocardium and the peripheral arteries, while antihypertensive treatment has, as first target, the cerebral vessels, with a very strong reduction in the risk of occurrence of new stroke. or recurrent (4).
Hypertension is above all the most modifiable vascular risk factor, with a remarkable level of scientific evidence, but an impact in terms of public health practice which can be further improved.
THE BASICS OF THIS MODIFIABLE EQUATION
Several facts are perfectly demonstrated.
The first target of hypertension: the brain This reality is based on numbers. In France, there is an average of 150,000 strokes per year compared to 130,000 myocardial infarctions.
Hypertension is present in 65% of ischemic strokes (AIC) and in 75% of hemorrhagic strokes (HCA) (5). Brain metabolism is based on two substrates, the variations of which are extremely harmful: glucose and oxygen. These two metabolites are closely dependent on the cerebral blood flow, which is high: between 50 and 60 ml / min per 100 g of tissue.
Any lowering of the cerebral blood flow on a vascular territory by an atherothrombotic phenomenon will modify the metabolism of the cerebral territory concerned, resulting in the deficit of the function supported by the atheromatous artery. This deficit will be transient if the ischemia does not lead to a heart attack; it will be prolonged, durable and massive if the ischemia results in a widespread infarction.
Blood pressure and risk of stroke Forty-five prospective studies were combined in the collaborative study that was published in 1995 (6). This epidemiological study based on 450,000 people detected 13,000 strokes and calculated that the incidence of strokes increases by 80% for each increase of 10 mmHg in diastolic blood pressure, and without a threshold value. It also calculated that the relative risk of stroke or stroke is quadrupled, while the relative risk of stroke is tenfold.
HTA: two types of stroke generated
Hypertension produces two types of stroke: one hemorrhagic, the other ischemic, which makes their management complex and specific.
HT is responsible for two diametrically opposed stroke mechanisms. Unlike myocardial accidents, the brain experiences two types of vascular accident: on the one hand, ischemic cerebral accidents, in particular concerning perforating arterioles, at the origin of small lacunar infarctions located specifically in the gray nuclei central and internal capsules, which represent 20% of strokes; on the other hand, a second mechanism unknown in the myocardial domain and which is represented by the hemorrhagic stroke, found in 15% of cases . The share of accidents hemorrhagic bleeding continues to decrease steadily in Western countries, a direct consequence of the beneficial effects of early detection and treatment of hypertension. These two types of stroke are to be integrated into all of the others mechanisms. Thus, we recognize ischemic strokes by atherothrombosis of large arterial trunks (30% of cases), ischemic strokes by atherothrombosis of perforating arterioles, also called gaps (20% of cases), cardio-embolic ischemic attacks, clearly increasing in western countries due to improved survival of heart patients at the cost of cerebrovascular complications (20% of cases), ischemic strokes of other nature and not atheromatous (arterial dissection, polycythemia, hypoglycemia) (5% of cases), and finally ischemic strokes with no etiology found (25% of cases) (4, 7, 8).
The interest of this classification is that it is both anatomopathological and physiopathological, and that it directs towards very specific etiology mechanisms with a relatively well correlated prognosis and leading to specific therapeutic, curative and preventive strategies justifying the taken in professionalized burden of stroke.
The last remark concerns the major role of magnetic resonance imaging and, failing that, of the scanner, capable of determining these different mechanisms.
Role of stroke in raising blood pressure in the acute phase Spontaneously, 50% of strokes are accompanied in the acute phase by hypertension greater than 160/90 mmHg (9), which is more frequent than for other acute brain conditions (10), involving pre-existing hypertension (9) and acute intracranial hypertension. Finally, the location of the stroke in the island
could be a source of labile hypertension (11).
This hypertension can have deleterious effects, which justified the first recommendations to decrease hypertension in the acute phase of stroke, because of the risk of hemorrhagic transformation and an edematous transformation of a cerebral infarction.