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Peter J. Mason,
JoAnn E. Manson, Marilyn J. Chown, Howard D. Sesso, Paul M. Ridker,
Robert J. Glynn
Objective:
Some studies suggest a J-shaped relationship between blood pressure
and cardiovascular disease (CVD) risk in treated hypertensives and
those with prior CVD. We examined the association of systolic blood
pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP),
and mean arterial pressure (MAP) with subsequent CVD events among
high-risk women participating in the Women's Antioxidant and Cardiovascular
Study (WACS).
Methods:
WACS, double-blind, placebo-controlled, secondary prevention trial
of the benefits and risks of antioxidant vitamins, randomized 8,171
women, including two strata: 5,951 women with prevalent CVD and
2,191 women with = 3 cardiac risk factors. At baseline, mean age
was 60.6 years, mean SBP was 135.3 mmHg and mean DBP was 81.8 mmHg,
among those reporting blood pressure at baseline (99.6%). The primary
outcome measure was a combined endpoint of confirmed nonfatal MI,
nonfatal stroke, coronary revascularization procedures (CABG or
PTCA), and CVD mortality.
Results:
To date 512 CVD events have been confirmed in this ongoing trial,
with a median follow-up of 4.2 years. We used stratified proportional
hazards models to examine the relationship of several components
of blood pressure with cardiovascular risk, controlling for age,
cigarette smoking, body mass index, elevated cholesterol, diabetes,
alcohol use, menopause, level of exercise, and use of antihypertensive
medications, We found no increased risk associated with low levels
of either SBP or DBP. Based upon a comparison of likelihood ratios,
SBP was a stronger predictor of CVD risk than DBP, PP or MAP. The
relationship of SBP with CVD risk was not linear: below 140 mmHg
there was no association with CVD risk. Compared to women with SBP
of 120-129 mmHg, those with SBPs of 140-159 and = 160 mmHg had proportional
hazard ratios of 1.22 (95% CI, 0.90-1.64) and 2.17 (95% CI, 1.49-3.14),
respectively. Results were similar for the women with prevalent
CVD and those with = 3 risk factors.
Conclusion:
SBP, as compared to other measurements of blood pressure, is the
strongest predictor of CVD risk among middle-aged women with known
CVD and in women with multiple cardiac risk factors. There does
not appear to be a J-shaped relationship between blood pressure
and CVD risk in the WACS study population.
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