METHODS: We conducted a population-based case-control study to examine the relation between treated diastolic blood pressure and the risk of primary cardiac arrest among hypertensive patients free of clinically diagnosed cardiovascular disease. Cases were hypertensive enrollees of the Group Health Cooperative of Puget Sound, an HMO, who had a primary cardiac arrest between 1977 and 1990 (n=80). Control patients were a stratified random sample of hypertensive enrollees (n=426). Ambulatory-care records were reviewed to assess blood pressures and other clinical characteristics. Medication use was assessed through the HMO computerized pharmacy database.

RESULTS: Logistic regression models suggested a curvilinear relation between the level of treated diastolic blood pressure and the risk of primary cardiac arrest, after adjustment for pretreatment diastolic blood pressure, antihypertensive therapy, and other potential confounders. Compared with a treated diastolic blood pressure of 85 mm Hg, a treated diastolic blood pressure of 80 mm Hg was associated with a small increase in risk (relative risk [RR] 1.2; 95% confidence interval [CI] 1.0, 1.6), 75 mm Hg was associated with a modest increase in risk (RR 1.6; 95% CI 1.2, 2.1), and 70 mm Hg was associated with more than a twofold increase in the risk of primary cardiac arrest (RR 2.3; 95% CI 1.4; 3.8). There was little evidence of effect modification by pretreatment diastolic blood pressure.

CONCLUSIONS: Our findings support available evidence that among hypertensive patients a treated diastolic blood pressure level below 85 mm Hg is associated with cardiac hazards.