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Is blood pressure treatment as effective in a population setting as in controlled trials? Results from a prospective
H L Thürmer1, P G Lund-Larsen, A Tverdal
1National Health Screening Service, Oslo, Norway.
Objective:
To evaluate the effectiveness of treatment in situations in which general practitioners and patients use medication according to their own judgement, and where selection, compliance and follow-up varies. This prospective population study differs from the efficacy of treatment studied in randomized trials.
Design:
Baseline (1974-1976) and repeat (1977-1981) cardiovascular screenings of all males aged 35-49 years in three counties in Norway, with mortality follow-up from the second screening until 1990.
Setting:
A nationwide ambulatory screening service reporting community results and referring high-risk subjects to their local general practitioners.
Participants:
A total of 21,314 males (86%) attended both screenings, of whom 840 took blood pressure medication at the second screening. Males with cardiovascular disease, diabetes or blood pressure treatment at baseline were excluded.
Main Outcome Measures:
Changes in coronary risk factors, mortality from all causes, coronary heart disease and non-cardiovascular causes.
Results:
The effect of treatment on blood pressure was small, and the attainment of reasonable target blood pressures was rare. The cholesterol level decreased and the level of triglycerides increased more in the treatment group than in the untreated group. Blood pressure treatment was associated with increased mortality in most risk strata, and at pretreatment systolic blood pressures up to 184 mmHg. A particularly high mortality rate was found when blood pressure increased despite treatment and at low pretreatment blood pressures. According to Cox proportional hazards analyses controlling for pretreatment blood pressure, cholesterol, age, smoking and body mass index, the relative risk of coronary heart disease death in the treatment group was 1.8 (95% confidence interval 1.3-2.6).
Conclusion:
The benefit experienced from the trials turned into an adverse effect of treatment in the population setting, particularly at low pretreatment blood pressure, and when blood pressure increased during treatment.