Distribution of a subclinical marker of cardiovascular risk, the ankle brachial index, in a rural African population: SASPI study

Background In sub-Saharan Africa, hypertension and stroke are emerging as an important cause of death and disability, whereas coronary heart disease appears still to be uncommon. The aim of our study was to measure for the first time in an African population the ankle brachial index (ABI), which is known to be a good marker of subclinical atheroma and of the risk of future cardiovascular events. Methods The study was part of the Southern African Stroke Prevention Initiative (SASPI). It comprised a cross-sectional survey conducted in rural north-east South Africa in the sub-district of Agincourt, in which the demography of the population has been closely monitored. A stratified sample of 10 villages were selected and within these a random sample was chosen of 526 men and women aged 35 years and older. Subjects were visited on up to three occasions to be interviewed and have a clinical examination by specially trained nurses. This included an assessment of cardiovascular risk factors and measurement of the ABI (ratio of ankle: brachial systolic pressure) using a Doppler ultrasound machine. Results The sample comprised 322 subjects in whom the mean ABI (lower of either leg) was 1.05 in both men and women. The distribution of ABI was negatively skewed and a low ABI of 0.9 or less, indicative of significant atheroma and higher cardiovascular risk, increased with age from 3.9% in 40-49 year olds to 39.7% in those aged 70 years and older. Lower ABI was related to current cigarette smoking (P = 0.02) and higher systolic and diastolic blood pressure (P < 0.01, P = 0.02, respectively) but not total cholesterol levels, which were relatively low in this population (mean 4.47 mmol/l). Conclusion The distribution of the ABI in this rural African population was very similar to that reported in western populations, and suggests that this population has subclinical peripheral atheroma and is at an increased risk of future cardiovascular events, thus providing further evidence of an epidemiological transition towards cardiovascular disease.