Hypertension in Stroke

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What is the epidemiology of stroke?

A stroke refers to the development of focal neurological symptoms such as the sudden loss of movement, sensation, or coordination that arises due to impaired blood flow to the brain or spinal cord. A transient ischemic attack (TIA) is a temporary period of symptoms similar to those of a stroke that resolves spontaneously. A TIA usually lasts only a few minutes and does not cause permanent damage. A TIA is often a warning sign of impending stroke.

Globally, stroke is the second largest cause of death (5·5 million deaths in 2016) after ischemic heart disease, and also the second most common cause of disability. There were 14 million incident and 80 million prevalent cases of stroke globally in 2016. There is significant geographical variation, with east Asia, followed by Eastern Europe having the highest incidence. Even in United States, the incidence of stroke is highest in the southeastern region, often referred to as the “stroke belt.” There is an increasing risk of stroke with increasing age, and a slightly higher risk for men compared to women, which equalizes approximately after the age of 80 years. In less developed regions, the average age of stroke is younger, likely due to the different population age structure and competing causes of death.

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What are the major classifications of stroke and which types are associated with hypertension?

Strokes are broadly classified as ischemic (88%) or hemorrhagic (12%). In ischemic stroke, an intracranial artery becomes blocked; in hemorrhagic stroke, it ruptures. The proportion of hemorrhagic strokes is higher in Asia, at about 20% to 30%. Common causes of ischemic stroke include small vessel disease, cardio emboli, and large artery atherosclerotic plaque rupture. About 20% of strokes are cryptogenic, in that a clear cause cannot be identified despite thorough investigations. An independent phenomenon that may present in a similar fashion is subarachnoid hemorrhage due to rupture of an intracranial aneurysm.

Hypertension is the primary cause of intracerebral hemorrhage, accounting for a population attributable risk of about 60%. Hypertension is also the primary cause of lacunar infarcts. The risk of stroke rises steadily as blood pressure level rises and doubles for every 7.5 mm Hg increment in diastolic blood pressure, with no lower threshold.

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What are the risk factors for stroke?

Risk factors for ischemic and hemorrhagic stroke are shown in Table 25.1 . Metabolic risk factors (high systolic blood pressure [BP], high body-mass index, high fasting plasma glucose, high total cholesterol, and low glomerular filtration rate) account for the major proportion of the attributable risk, followed by behavioral factors (smoking, poor diet, and low physical activity), and environmental risks (e.g., air pollution and lead exposure).

The relationship of stroke mortality to usual BP is strong and direct at all ages, with no good evidence of a threshold at any age in the range of usual systolic BP (SBP) above 115 mm Hg or of usual diastolic BP (DBP) above 75 mm Hg. At ages 40 to 69 years, each difference of 20 mm Hg usual SBP (or ∼ 10 mm Hg usual DBP) is associated with more than a twofold difference in the stroke death rate. See Fig. 25.1 for a representation of this risk from a systematic review of multiple cohorts including about one million individuals.

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