The relevance of different methods of calculating the ankle-brachial index: the multi-ethnic study of atherosclerosis

Abstract

The authors aimed to determine differences in the prevalence of peripheral arterial disease (PAD) and its associations with cardiovascular disease (CVD) risk factors, using different methods of calculating the ankle-brachial index (ABI). Using measurements taken in the bilateral brachial, dorsalis pedis, and posterior tibial arteries, the authors calculated ABI in 3 ways: 1) with the lowest ankle pressure (dorsalis pedis artery or posterior tibial artery) ("ABI-LO"), 2) with the highest ankle pressure ("ABI-HI"), and 3) with the mean of the ankle pressures ("ABI-MN"). For all 3 methods, the index ABI was the lower of the ABIs calculated from the left and right legs. PAD was defined as an ABI less than 0.90. Among 6,590 subjects from a multiethnic cohort (baseline examination: 2000-2002), in comparison with ABI-HI, the relative prevalence of PAD was 3.95 times higher in women and 2.74 times higher in men when ABI-LO was used. The relative magnitudes of the associations were largest between PAD and both subclinical atherosclerosis and CVD risk factors when ABI-HI was used, except when risk estimates for PAD were less than 1.0, where the largest relative magnitudes of association were found using ABI-LO. PAD prevalence and its associations with CVD risk factors and subclinical atherosclerosis measures depend on the ankle pressure used to compute the ABI.

Figure 1.

Associations between peripheral arterial disease (PAD), determined using different methods of calculating the ankle-brachial index (ABI), and selected subclinical measures of atherosclerosis, Multi-Ethnic Study of Atherosclerosis, 2000–2002. “CAC > 0” = coronary artery calcium (CAC) score greater than 0; “CAC difference” = difference in CAC score between subjects with PAD and subjects without PAD; “Q4 CAC” = highest (fourth) quartile of CAC; and “Q4 CCA-IMT” = highest (fourth) quartile of common carotid artery intima-media thickness (CCA-IMT). Values for “CAC > 0,” “Q4 CAC,” and “Q4 CCA IMT” are relative prevalences; values for “CAC difference” are differences in log-transformed mean values. Results were adjusted for age, gender, ethnicity, smoking status, hypertension, dyslipidemia, and diabetes. Bars, 95% confidence interval.