Prevalence and outcomes of low ankle brachial index by atherosclerotic cardiovascular disease risk level: Insights from the National Health and Nutrition Examination Survey (NHANES)

Background: Ankle brachial index (ABI) as a risk-enhancing factor in addition to the pooled cohort equation (PCE) in assessing cardiovascular risk for primary prevention of atherosclerotic cardiovascular disease (ASCVD) is uncertain.

Methods: We analyzed data from the 1999-2004 National Health and Nutrition Examination Survey (NHANES), for 5130 participants, aged 40 and older, without known cardiovascular disease or diabetes, with available data on standard ASCVD risk and ABI. Prevalence of low ABI (ABI<0.9) and all-cause mortality in persons with low, borderline and intermediate ASCVD risk categories using PCE was assessed.

Results: The overall prevalence of low ABI was 3.1%. The participants with low ABI were predominantly clustered in the intermediate (33%) and high (33%) ASCVD risk categories while most participants with a normal ABI were in the low (56%) and intermediate (23%) risk categories. All-cause mortality was higher among participants with low ABI compared to those with a normal ABI in both the intermediate/borderline and high-risk categories, p<0.001 but not in the low-risk ASCVD category, p = 0.323.

Conclusions: Using the PCE, two-third of the participants with low ABI were classified as having a low, borderline or intermediate risk of ASCVD. Low ABI was associated with an increased all-cause mortality in the overall cohort and specifically among those with a borderline/intermediate or high risk of ASCVD but not in those with a low risk of ASCVD. Our study supports consideration of ABI as a risk enhancer for primary prevention among patients classified as borderline or intermediate risk of ASCVD.