Hypertension control and the risk of myocardial infarction and stroke: a population-based study

A population-based case-control study was performed to determine the importance of the presence of hypertension and the control of blood pressure level during treatment for hypertension on the occurrence of acute myocardial infarction (AMI) and stroke in persons aged 35-69 years in the Hunter Region community. Patients with a first episode of AMI or stroke were identified from community-based heart attack and stroke registers and compared with control subjects obtained from a random population sample from the same community. Twenty per cent of control subjects were currently receiving treatment for hypertension compared with 37% of patients with myocardial infarction (odds ratio adjusted for age, sex and several other possible confounding variables, 2.6; 95% confidence interval (CI), 1.9-3.4) and 51% of patients with stroke (adjusted odds ratio, 3.5; 95% CI, 2.3-54). Among those who had ever been told they had hypertension, 71%, 73% and 59% of patients with AMI, patients with stroke and control subjects, respectively, were receiving treatment at the time of the AMI or the stroke or at the time of the survey (control subjects). For those receiving treatment for hypertension, blood pressure levels were obtained from the records of their general practitioner. Despite similar pretreatment levels the last recorded blood pressure level (either before the survey of the development of AMI or stroke) was higher among those who developed AMI or stroke than those in the control group. Those with a treated diastolic blood pressure of less than 80 mmHg appeared to be at a higher risk of both AMI and stroke than those with a treated diastolic blood pressure level of 80-89 mmHg, but the difference was not statistically significant. Randomised controlled trials do not show a reduction in rates of AMI in response to a reduction of blood pressure. Nevertheless our findings suggest that the presence of hypertension and poor control of blood pressure levels despite treatment may be important aetiologically both for AMI and stroke occurrence.