Blood pressure and the prevention of stroke.

RELATIONSHIP BETWEEN BLOOD PRESSURE AND STROKE: Data from prospective observational studies indicate that usual levels of blood pressure are directly and continuously related to the risk of initial stroke. A prolonged difference in usual blood pressure levels of just 9/5 mmHg is associated with approximately a one-third difference in stroke risk, with similar proportional effects in hypertensives and normotensives. Recent data from studies of individuals with a history of cerebrovascular disease indicate a similar association between blood pressure and the risk of recurrent stroke. EFFECTS OF TREATMENT ON STROKE: The results of randomized trials of blood pressure-lowering drugs in hypertensive patients suggest that much or all of the long-term potential stroke avoidance associated with prolonged blood pressure differences can be achieved within just a few years of beginning treatment. Overall, in 17 randomized trials of antihypertensive treatment a net blood pressure reduction of 10-12 mmHg systolic and 5-6 mmHg diastolic conferred a reduction in stroke incidence of 38% (SD 4), with similar reductions in fatal and non-fatal stroke. Because the proportional effects of treatment were similar in higher and lower risk patient groups, the absolute effects of treatment on stroke varied in direct proportion to the background risk of stroke. The greatest potential benefits were observed among those with a history of cerebrovascular disease; however, the results of the trials conducted in patients with a history of stroke or transient ischaemic attack, although promising, were not definitive. New trials are required to determine more reliably the effects of blood pressure lowering in patients with cerebrovascular disease.