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CLINICAL RESEARCH: PERIPHERAL VASCULAR DISEASE

Associations of Borderline and Low Normal Ankle-Brachial Index Values With Functional Decline at 5-Year Follow-Up

The WALCS (Walking and Leg Circulation Study)

Mary M. McDermott, MD^_*,,_*, Jack M. Guralnik, MD, PhD, Lu Tian, ScD, Kiang Liu, PhD, Luigi Ferrucci, MD, PhD, Yihua Liao, MS, Leena Sharma, MD^_* and Michael H. Criqui, MD, MPH^||

^_* Department of Medicine, Northwestern University's Feinberg School of Medicine, Chicago, Illinois
Department of Preventive Medicine, Northwestern University's Feinberg School of Medicine, Chicago, Illinois
Laboratory of Epidemiology, Demography, and Biometry, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
Laboratory of Clinical Epidemiology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
^|| Department of Family and Preventive Medicine, University of California at San Diego, San Diego, California

Manuscript received February 25, 2008; revised manuscript received August 18, 2008, accepted September 10, 2008.

^_* Reprint requests and correspondence: Dr. Mary M. McDermott, 750 North Lake Shore Drive, 10th Floor, Chicago, Illinois 60611 (Email: mdm608{at}northwestern.edu).

Objectives: We studied associations of borderline and low normal ankle-brachial index (ABI) values with functional decline over a 5-year follow-up.

Background: The associations of borderline and low normal ABI with functional decline are unknown.

Methods: The 666 participants included 412 with peripheral arterial disease (PAD). Participants were categorized as follows: severe PAD (ABI <0.50), moderate PAD (ABI 0.50 to 0.69), mild PAD (ABI 0.70 to 0.89), borderline ABI (0.90 to 0.99), low normal ABI (1.00 to 1.09), and normal ABI (ABI 1.10 to 1.30). Outcomes were assessed annually for 5 years. Mobility loss was defined as loss of the ability to walk one-quarter mile or walk up and down 1 flight of stairs without assistance among participants without baseline mobility impairment. Becoming unable to walk for 6 min continuously was defined as stopping during the 6-min walk at follow-up among those who walked for 6 min continuously at baseline. Results were adjusted for age, sex, race, comorbidities, and other confounders.

Results: Hazard ratios (HRs) for mobility loss according to ABI category were as follows: severe PAD, HR: 4.16 (95% confidence interval [CI]: 1.58 to 10.92); moderate PAD, HR: 3.82 (95% CI: 1.66 to 8.81); mild PAD, HR: 3.22 (95% CI: 1.43 to 7.21); borderline ABI, HR: 3.07 (95% CI: 1.21 to 7.84); and low normal ABI, HR: 2.61 (95% CI: 1.08 to 6.32; p trend = 0.0018). Similar associations were observed for becoming unable to walk for 6 min continuously (p trend < 0.0001).

Conclusions: At 5-year follow-up, persons with borderline ABI values have a higher incidence of mobility loss and becoming unable to walk for 6 min continuously compared with persons who have a normal baseline ABI. A low normal ABI is associated with an increased incidence of mobility loss compared with persons who have a normal ABI.

Key Words: ankle-brachial index • physical functioning • peripheral arterial disease • intermittent claudication

Abbreviations and Acronyms   ABI = ankle-brachial index   BMI = body mass index   CI = confidence interval   HR = hazard ratio   PAD = peripheral arterial disease

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