Control of blood pressure and risk of stroke among pharmacologically treated hypertensive patients

Background and Purpose-Despite improved control of blood pressure during th e last decades in the United States, a considerable proportion of treated h ypertensives have not achieved target blood pressure levels. We estimated t he proportion of strokes occurring among treated hypertensive patients that may be attributable to uncontrolled blood pressure. Methods-A population-based case-control study was conducted among treated h ypertensive members of Group Health Cooperative of Puget Sound. Cases were treated hypertensive patients who sustained a first fatal or nonfatal, isch emic (n = 460) or hemorrhagic (n = 95) stroke during 1989-1996, Controls we re a random sample of stroke-free, treated hypertensive Group Health Cooper ative enrollees (n = 2966), similar in age to the stroke cases. Multiple me asurements of blood pressure and other cardiovascular risk factors were col lected from medical records. Logistic regression was used to estimate the r isk of ischemic stroke and hemorrhagic stroke associated with uncontrolled blood pressure, defined as diastolic blood pressure >90 mm Hg or systolic b lood pressure >140 mm Hg. The fraction of strokes attributable to uncontrol led blood pressure among treated hypertensives was calculated. Results-Blood pressure was uncontrolled in 78% of ischemic stroke cases, 85 % of hemorrhagic stroke cases, and 65% of controls. After adjustment for po tential confounders, uncontrolled blood pressure among treated hypertensive patients was moderately associated with ischemic stroke (risk ratio = 1.5 [95% CI, 1.3 to 1.9]) and strongly related to hemorrhagic stroke (risk rati o = 3.0 [95% CI, 1.7 to 5.4]). We estimated that 27% (95% CI, 11% to 39%) o f the ischemic strokes and 5740 (95% CI, 26% to 75%) of the hemorrhagic str okes among treated hypertensive patients were attributable to uncontrolled blood pressure. Overall, 32% (95% CI, 14% to 45%) of all strokes were attri butable to uncontrolled blood pressure, Conclusions-A considerable proportion of incident strokes among treated hyp ertensive patients may be prevented by achieving control of blood pressure.