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Using the ankle-brachial index to diagnose peripheral artery disease and assess cardiovascular risk

Cleveland Clinic Journal of Medicine. 2012 September;79(9):651-661 | 10.3949/ccjm.79a.11154
September 1, 2012|Cleveland Clinic Journal of Medicine
Esther S.H. Kim, MD, MPH;Keattiyoat Wattanakit, MD, MPH;Heather L. Gornik, MD, MHS
Author and Disclosure Information

Esther S.H. Kim, MD, MPH
Vascular Medicine Section, Department of Cardiovascular Medicine, Heart and Vascular Institute, Cleveland Clinic

Keattiyoat Wattanakit, MD, MPH
HeartCare Midwest, Peoria, IL

Heather L. Gornik, MD, MHS
Vascular Medicine Section, Department of Cardiovascular Medicine, Heart and Vascular Institute, Cleveland Clinic

Address: Heather L. Gornik, MD, MHS, Non-Invasive Vascular Laboratory,
Cleveland Clinic Heart and Vascular Institute, J35, 9500 Euclid Avenue,
Cleveland, OH 44195; e-mail gornikh@ccf.org

Dr. Gornik has received research grant support from Summit Doppler Systems, Inc, and is a named co-inventor on a patent related to the noninvasive diagnosis of peripheral artery disease for which she may receive royalties.

ABSTRACTThe ankle-brachial index is valuable for screening for peripheral artery disease in patients at risk and for diagnosing the disease in patients who present with lower-extremity symptoms that suggest it. The ankle-brachial index also predicts the risk of cardiovascular events, cerebrovascular events, and even death from any cause. Few other tests provide as much diagnostic accuracy and prognostic information at such low cost and risk.

KEY POINTS

  • The ankle-brachial index is the systolic pressure in the ankle (either the dorsalis pedis or the posterior tibial artery, whichever has the higher pressure) divided by the systolic pressure in the arm (either the left or right, whichever is higher). The lower of the two values obtained (left and right) is the patient’s overall ankle-brachial index.
  • Most healthy adults have a value greater than 1.0. A value of less than 0.91 indicates significant peripheral artery disease, and a value lower than 0.40 at rest generally indicates severe disease. Values higher than 1.4 indicate stiffened, noncompressible arteries.
  • Measuring the ankle-brachial index after exercise can uncover peripheral artery disease in patients with a normal resting ankle-brachial index.

THE ANKLE-BRACHIAL INDEX AS A MARKER OF RISK

Low values: Peripheral artery disease

Adapted from McKenna M, et al. The ratio of ankle and arm arterial pressure as an independent predictor of mortality. Atherosclerosis 1991; 87:119–128; with permission from Elsevier.
Figure 2. Survival curves from 744 patients followed after ankle-brachial index testing at a single community hospital. The 5-year survival rate in patients with values < 0.4 was 44%, compared with 90% in patients with values > 0.85.

Peripheral artery disease, as diagnosed by a low ankle-brachial index, confers an excess risk of death from all causes in a graded fashion: ie, the more severe the disease, the lower the survival rate (Figure 2).34 Because peripheral artery disease is a sign of systemic atherosclerosis and one-third to one-half of patients with peripheral artery disease have evidence of cerebrovascular or coronary artery disease,35–37 peripheral artery disease also confers a higher risk of cardiovascular death.

The Edinburgh Artery Study,38 a prospective cohort study of 1,592 randomly selected patients age 55 to 74 years, demonstrated the relationship between a low ankle-brachial index and an increased risk of cardiovascular death. Over 5 years of follow-up, compared with patients with a normal ankle-brachial index, the relative risk of cardiovascular death in symptomatic patients with a value of 0.9 or lower was 2.67 (95% confidence interval [CI] 1.34–5.29). The relative risk in patients with asymptomatic disease was between 1.74 (95% CI 1.09–2.76) and 2.08 (95% CI 1.13–3.83), depending on the level of ankle-brachial index decrement and ankle blood pressure response to hyperemia.

(Reactive hyperemia is an alternative to exercise testing. It is performed by inflating a blood pressure cuff at the thigh above the systolic pressure for 3 to 5 minutes or until the patient can no longer tolerate the inflation. Blood pressures at the ankle are remeasured after cuff release.)

Several other epidemiologic studies have established the association between low ankle-brachial index and the risk of cardiovascular death.

Heald et al39 performed a meta-analysis of 44,590 patients in 11 epidemiologic studies and found that, after adjustment for age, sex, conventional cardiovascular risk factors, and prevalent cardiovascular disease, an ankle-brachial index lower than 0.9 conferred a higher risk of:

  • All-cause mortality (pooled risk ratio [RR] 1.60, 95% CI 1.32–1.95)
  • Cardiovascular mortality (pooled RR 1.96, 95% CI 1.46–2.64)
  • Coronary heart disease (pooled RR 1.45, 95% CI 1.08–1.93)
  • Stroke (pooled RR 1.35, 95% CI 1.10–1.65).

Fowkes et al,40 in a meta-analysis of 16 population cohort studies including 48,294 patients over 480,325 person-years of follow-up, found that a low ankle-brachial index predicted cardiovascular events and death even after adjusting for the Framingham risk score, Hazard ratios for cardiovascular death were:

  • 2.92 (95% CI 2.31–3.70) in men
  • 2.97 (95% CI 2.02–4.35) in women.

Hazard ratios for death from any cause were:

  • 2.34 (95% CI 1.97–2.78) in men
  • 2.35 (95% CI 1.76–3.13) in women.

Adding the ankle-brachial index to the Framingham risk score resulted in reclassification of risk category in approximately 19% of men and 36% of women.40

Adapted from Diehm C, et al. Mortality and vascular morbidity in older adults with asymptomatic versus symptomatic peripheral artery disease. Circulation 2009; 120:2053–2061; with permission of Lippincott Williams &amp; Wilkins.
Figure 3. Kaplan-Meier curves in the German Epidemiological Trial on Ankle Brachial Index (getABI). The difference in event-free survival between patients with symptomatic vs asymptomatic peripheral artery disease was largely driven by peripheral revascularization procedures.

The German Epidemiological Trial on Ankle Brachial Index (getABI) screened 6,880 patients 65 years of age and found an abnormal ankle-brachial index in 20.9% of them.41 In more than 5 years of follow-up, a value of less than 0.90 was associated with a higher rate of cardiovascular events and death from any cause in patients with both symptomatic and asymptomatic peripheral artery disease (Figure 3).41

In addition, the lower the ankle-brachial index, the greater the rate of death or severe cardiovascular events. An index between 0.7 and 0.9 was associated with a statistically significant twofold increase (adjusted hazard ratio 2.03), and a value lower than 0.5 was associated with a nearly fivefold increase (hazard ratio 4.65) in the risk of events compared with the group of patients with normal values.41

Abnormal results after exercise

Exercise testing may increase the sensitivity of the ankle-brachial index to detect peripheral artery disease in patients with normal resting values and especially in patients with borderline values. As such, abnormal exercise values have also been associated with an increased risk of death due to any cause and of cardiovascular death.

In a prospective cohort study of 3,209 patients with suspected or known peripheral artery disease referred to a vascular surgery clinic in the Netherlands, patients with lower postexercise values had a higher rate of overall and cardiac death (hazard ratio per 10% lower value 1.16 [95% CI 1.13–1.18] and 1.10 [95% CI 1.09–1.13], respectively).42

Sheikh et al43 reported similar findings in patients with normal resting ankle-brachial indices at Cleveland Clinic. In this study, an abnormal postexercise ankle-brachial index (defined as < 0.85) was associated with a hazard ratio of 1.67 for all-cause mortality compared with a normal postexercise value among individuals with no history of cardiovascular events.

High values: Noncompressible vessels

While the relationship between low values and increased mortality and cardiovascular risk is well accepted, there have been conflicting reports regarding high values (> 1.4) and adverse outcomes.44,45

Adapted with permission from Resnick HE, et al. Relationship of high and low ankle brachial index to all-cause and cardiovascular disease mortality: the Strong Heart Study. Circulation 2004; 109:733–739.
Figure 4. Data from 4,393 patients in the Strong Heart Study according to baseline ankle-brachial index. Patients were followed for a mean of 8.3 years. All-cause (white bar) and cardiovascular-disease-related (black bar) mortality rates were lowest in people with values of 1.0 to 1.4.

The Strong Heart Study44 was a population-based study in 4,393 Native Americans followed for more than 8 years for the rate of all-cause and cardiovascular mortality. Most (n = 3,773) of the cohort had a normal ankle-brachial index (≥ 0.9 and ≤ 1.4); 4.9% (n = 216) had a low value (< 0.9); and 9.2% (n = 404) had a high value (> 1.4 or noncompressible). Relative risk ratios for all-cause mortality were 1.69 (95% CI 1.34–2.14) for low values and 1.77 (95% CI 1.48–2.13) for high values compared with those with normal values. Low and high ankle-brachial indices also conferred a risk of cardiovascular death, with relative risk ratios of 2.52 (95% CI 1.74–3.64) and 2.09 (95% CI 1.49–2.94), respectively. There was a U-shaped relationship between the ankle-brachial index and the mortality rate (Figure 4).44

The Atherosclerosis Risk in Communities (ARIC) study45 had different findings. In 14,777 participants followed for a mean of 12.2 years, the cardiovascular disease event rates of patients whose ankle-brachial index-was categorized as high (> 1.3, > 1.4, or > 1.5) were similar to those of patients with a normal value (between 0.9 and 1.3).

Differences in event rates between the two studies may be due to a higher prevalence of values greater than 1.4 in the Strong Heart Study cohort as well as to a higher prevalence of concomitant risk factors (diabetes, older age, hypertension, lipid abnormality) in the high ankle-brachial index group in the Strong Heart Study compared with the ARIC study.

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