Purpose: To examine how hypertension interacts with other known risk factors in affecting the risk of stroke in a primary care based setting.
Methods: Cases were patients with first-ever stroke identified from the community-based stroke register in 1994-95 in northwest England. Two controls per case were randomly selected from the same primary care site and matched by age and sex. Information on predefined risk factors was extracted from medical records.
Results: 267 cases and 534 controls were included. Adjusted odds ratio (OR) for stroke from hypertension was 2.6 (95% confidence interval: 1.7-3.9). In hypertensives who were current smokers, risk of stroke was increased 6 fold as compared to non-smokers without hypertension. Hypertensives who had a preexisting history of myocardial infarction or obesity or diabetes had 3 fold higher risks of stroke. Subjects with hypertension and with a history of transient ischemic attack or atrial fibrillation had > or = 8 fold excess risk of stroke. Among them, the risk was greater in those with poorly controlled or untreated hypertension and in those with well or moderately controlled as compared to subjects without both risk factors. There appeared to be a steady increase in risk of stroke according to the number of risk factors present, particularly in hypertensive subjects.
Conclusions: Stroke risks in hypertensives associated with combinations of other risk factors appeared to follow an additive model. Subjects with multiple risk factors should be targeted in order to reduce the overall risk for stroke.