Standard Screening Tool for Peripheral Artery Disease (PAD) Can Identify Patients at Higher Risk of Functional Decline and Disab
Experts call for rethinking of clinical threshold for “normal” ABI
People with borderline or low normal ankle-brachial index (ABI) — the ratio of systolic blood pressure at the ankle compared to that in the arm — who are considered “normal” based on current screening guidelines have a two- to three-fold higher risk for mobility loss, according to data published in the March 24, 2009 issue of the Journal of the American College of Cardiology.
“This study confirms that patients with peripheral artery disease, defined as an ABI value below 0.90, experience significant and progressive loss of function and mobility,” said study author Mary McDermott, M.D., professor of Medicine, Northwestern University’s Feinberg School of Medicine, Chicago, Il. “But even those with borderline or low normal ABI also appear to be at significantly greater risk of functional declines, including losing the ability to walk up a flight of stairs or walk a quarter of a mile without assistance, compared to people who have no evidence of PAD based on ABI values between 1.10 and 1.30.”
This prospective, observational study — the first to look specifically at functional outcomes related to ABI measures at five-year follow up — finds that patients with ABI values between 0.90 and 1.09 had higher rates of mobility loss compared to people with a normal baseline ABI of 1.10 to 1.30. They were also more likely to progress to an ABI of less than 0.90 during the 5-year follow up than are people with an ABI of 1.10 and above.
These data add to a growing body of evidence that suggests ABI values between 0.90 and 1.09 are, indeed, clinically significant, according to Dr. McDermott. In other studies, low normal and borderline ABI measures have been found to be associated with increased cardiovascular event rates and early signs of artherosclerosis.
“This study shows that people we have not previously labeled as having significant PAD, those with borderline ABI values, are at high risk for disease progression and decline in function over time,” says Heather Gornik, MD, medical director, Non-Invasive Vascular Laboratory, Cleveland Clinic, and author of the accompanying editorial. “Given these and other data, the ‘normal’ value of 0.91 or greater needs to be revisited, and perhaps even raised to 1.10.”
Participants (n=666) were part of the WALCS (Walking and Leg Circulation Study) designed to identify predictors of functional decline in people with and without PAD. Of these, 62 percent had PAD. Participants underwent baseline assessments and an annual ABI measurement, functional assessment, a six-minute walk test, and questionnaire for mobility loss for up to 5 years. Average follow-up was 54 months. Patients were categorized according to normal ABI (1.10 to 1.30), PAD (ABI Mobility loss was defined as becoming unable to walk up and down one flight of stairs or walk one-quarter mile without assistance. A separate outcome was becoming unable to walk for six minutes continuously without stopping. Twenty-two patients who had mobility disability at baseline were excluded from the analyses of mobility loss.
Participants unable to walk for six minutes without stopping at the baseline visit were excluded from the analyses of becoming unable to walk for six-minutes continuously at follow-up. Lower ABI values were associated with significantly higher rates of mobility loss even after adjusting for age, sex, race, comorbidities, smoking, body-mass index and physical activity level.
“People with lower ABI values got worse over time. Prior research shows that patients with PAD often begin limiting their activities. In some cases, leg symptoms can go away as physical activity declines, creating the false impression that the patient is getting better because they no longer have symptoms,” said Dr. McDermott. “More research is needed to identify strategies that help prevent mobility loss and functional decline among patients, especially as the population ages and more Americans are living with PAD.”
Dr. McDermott reports no conflict of interest.