Blood pressure, antihypertensive treatment and stroke risk.

ASSOCIATION 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 stroke. The strength of this association has been substantially underestimated by many previous analyses that have not taken account of the regression dilution bias; correction for this increases the strength of the association between blood pressure levels and stroke risk by about 60%. From corrected analyses it is apparent that a prolonged difference in usual systolic/diastolic blood pressure levels of just 9/5 mmHg would eventually confer about a one-third difference in stroke risk, with similar proportional effects in hypertensives and normotensives. RESULTS OF CLINICAL TRIALS: The results of randomized trials of antihypertensive drugs suggest that much or all of the long-term potential stroke avoidance associated with this level of prolonged blood pressure difference 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 strokes. Additionally, the sizes of the reductions were similar in trials in mild, moderate and more severe hypertension, in trials in older and younger patients and in trials in patients with a history of cerebrovascular disease and in patients without such a history.
CONCLUSIONS: Because the proportional effects of treatment were similar in all these groups, the absolute effects of treatment on stroke varied in direct proportion to the background risk of stroke. Thus the greatest benefits were observed among those with a history of cerebrovascular disease, those above the age of 60 years and those with more severe hypertension.