Ankle-Brachial Index Can Identify Asymptomatic Individuals at Increased Risk

May 24, 2006

"[According to a new data analysis,] it is now time to evaluate the potential of incorporating the ABI into population-based cardiovascular prevention programs."

Although not routinely assessed in common clinical practice, the ankle-brachial index (ABI) is a relatively simple test for predicting the severity of peripheral arterial disease (PAD). The ABI is the ratio of systolic blood pressure in the ankle to that in the arm, and the American Heart Association describes the ABI as "a simple (patient acceptable) and inexpensive diagnostic test that among well-trained operators has excellent test-retest reliability." As a point of reference, a resting ABI of 1 or 1.1 is regarded as normal and < 1 as abnormal.

Now, according to the results of a new analysis published on April 16 in Atherosclerosis online, [1] in people who are symptomatic for PAD, the ABI can serve to identify people at increased risk for cardiovascular events. Reviewing recent studies in which the ABI was measured in people with no particular symptoms or history of disease, researchers from the University of Edinburgh Medical School (Edinburgh, United Kingdom) found that a low ABI was consistently associated with subsequent all-cause mortality, cardiovascular mortality, coronary artery disease, or stroke. The group, headed by Jacqueline F Price, MB ChB, Clinical Lecturer at the Wolfson Unit for the Prevention of Peripheral Vascular Diseases, believes that "It is now time to evaluate the potential of incorporating the ABI into population-based cardiovascular prevention programs."

Since PAD is associated with other forms of atherosclerosis, a number of individual studies have investigated the link between ABI and the risk of cardiovascular morbidity and mortality in the general population. However, this is the first time that a comprehensive, systematic review of the ABI as a marker of all-cause mortality and cardiovascular mortality and morbidity has been carried out, Dr. Price and her colleagues believe.

The Edinburgh researchers identified 11 "high-quality, population-based cohort studies," each of which recorded both the ABI at baseline and outcome events (including coronary heart disease, myocardial infarction, and stroke) during follow-up. The studies comprised a total of 44,590 people, followed for period of 4-12 years, in the United States and Europe. Most of the studies reported the relative risk of an outcome based on an ABI cut-off of 0.9.

Multivariate analysis of all of the results, adjusted for age, sex, conventional cardiovascular risk factors, and prevalent cardiovascular disease, showed that an ABI < 0.9 was associated with a 60% increased risk for all-cause mortality, 96% increased risk for cardiovascular mortality, 45% increased risk for coronary heart disease, and 35% increased risk for stroke (Table).

Table. Pooled Age- and Sex-Adjusted Relative Risks Associated With ABI < 0.9.
Outcome Pooled RR P
All-cause mortality 1.60 < .00001
Cardiovascular and cerebrovascular mortality 1.96 < .00001
Fatal and nonfatal coronary heart disease 1.45 .01
Fatal and nonfatal stroke 1.35 .003

The association between ABI and subsequent disease was seen across a range of age groups and in both sexes.

"Our review lends considerable support to the [American Heart] Association's assertion that the ABI is now emerging as a powerful and independent marker of future coronary events" (and of fatal cardiovascular events and stroke), said Dr. Price. "It also supports the recommendation that an ABI < 0.9 may be a useful addition to the assessment of disease risk in selected populations, including people whose risk assessment is neither clearly low risk nor high risk as assessed by presence or absence of traditional risk factors and people aged 50 years and over."

The researchers believe that by adding the ABI to risk formulas such as the Framingham Risk Score, their sensitivity, specificity, and predictive values will be increased.

Reference
  1. Heald CL, Fowkes FG, Murray GD, Price FK; the Ankle Brachial Index Collaboration. Risk of mortality and cardiovascular disease associated with the ankle-brachial index: systematic review. Atherosclerosis. 2006 [published online ahead of print, April 16].

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