Background--In apparently healthy people, the relation between blood pressure and risk of subsequent cardiovascular disease (CVD) is linear. In persons with CVD, the relation is uncertain.

Methods and Results--We conducted a prospective study of 5218 older women with CVD who reported their blood pressure at baseline in the Women’s Antioxidant Cardiovascular Study (WACS), an ongoing double-blind, placebo-controlled secondary prevention trial of the benefits and risks of antioxidant vitamins, folic acid, vitamin B₆, and vitamin B₁₂ among women with CVD or 3 coronary risk factors. A total of 661 confirmed CVD events (nonfatal myocardial infarction, nonfatal stroke, coronary artery bypass graft procedure, percutaneous coronary angioplasty, or CVD death) occurred during a median follow-up of 6.5 years. After controlling for age, randomized treatment assignment, antihypertensive medication use, and coronary risk factors, we found that systolic blood pressure (SBP) was a strong predictor of CVD events and that the relation between SBP and CVD risk was positive, continuous, and linear (P for linear trend=0.001). For each 10-mm Hg increment in SBP, there was a 9% (95% CI 4% to 15%) increase in risk of secondary CVD events. Diastolic blood pressure, mean arterial pressure, and pulse pressure were weaker predictors of CVD risk in this cohort, and joint consideration of SBP and diastolic blood pressure found that only SBP significantly predicted risk. Use of antihypertensive medication did not modify the relationship of SBP with CVD events.

Conclusions--In this population of women with CVD, we observed a strong, continuous, and linear association between SBP and risk of secondary CVD events. SBP was the blood pressure measure most strongly related to CVD risk.