Impact of Body Mass Index on the Association of Ankle-Brachial Index With All-Cause and Cardiovascular Mortality: Results from the National Health and Nutrition Examination Survey

OBJECTIVE: To assess the influence of body-mass index (BMI) on the association of ankle-brachial index (ABI) with mortality. PATIENTS AND METHODS: We conducted a prospective study of National Health and Nutrition Examination Survey participants enrolled from January 1, 1999 to December 31, 2002 with BMI and ABI data available. ABI categories were <0.9 (low), 0.9 to 1.3 (reference), and >1.3 (high). BMI categories were <30 kg/m(2) (nonobese) and ≥30 kg/m(2) (obese). Cardiovascular (CV) and all-cause mortality were assessed by National Death Index records. Cox proportional-hazards models and Kaplan-Meier survival estimates were used to compare groups. RESULTS: In total, 4614 subjects were included, with mean age 56±12 years and BMI 28±6 kg/m(2). Median follow-up was 10.3 years (interquartile range [IQR]: 9.3 to 11.4 years). Low and high ABI were present in 7% and 8%, respectively. After adjustment, low ABI was associated with increased all-cause and CV mortality in nonobese (hazard ratio [HR] 1.5, 95% CI, 1.1-2.1 for all-cause and 3.0 [1.8-5.1] for CV mortality) and obese individuals (1.8 [1.2-2.7] and 2.5 [1.2-5.6], respectively) compared with reference. High ABI was associated with increased CV mortality in nonobese (2.2 [1.1-4.5]) but not obese patients; it was not associated with all-cause mortality overall or when stratified by BMI. CONCLUSION: In a US cohort, weight influenced the prognostic significance of high ABI. This may be related to technical factors reducing compressibility of the calf arteries in obese persons compared with those who are nonobese.