The Ankle-Brachial Index: Candidate Marker for Cardiovascular Disease

Earlier commentaries in this series on cardiovascular (CV) risk addressed serum markers (eg, C-reactive protein, TNF-alpha inhibitors) and their potential role in CV event prediction. Investigation into the utility of these and other “candidate biomarkers” is increasingly popular-but why? The measurements are noninvasive, and although they are imperfect in conferring risk when applied alone, used in combination with major risk factors and other evaluations, they contribute valuable information. Identifying individuals with higher CV risk before a serious CV event occurs is an important, potentially lifesaving goal. Finding tests that are both noninvasive and inexpensive, and at the same time, capable of stratifying risk is worth the effort.

This brings us to a simple, noninvasive, primary care tool that is underused-the ankle-brachial index or, ABI.

The ABI is without question one of the simplest and least invasive tests in our armamentarium. It should be used more frequently as a screening tool in primary care practice.

Most “healthy” adults have an ABI of greater than 1. A value of less than 0.91 is consistent with peripheral vascular disease (PVD).¹ But an abnormal result tells us much more than whether or nor PVD is present. An abnormal ABI prescribes specific care¹:

1. Cardiovascular risk factor assessment,
2. Treatment of symptoms caused by intermittent claudication, and
3. Foot care to obviate vascular complications and amputations

And, ABI-confirmed PVD triggers the following treatments to reduce CV risk factors¹:

1. Aspirin (75 to 325 mg/d) or clopidogrel (75 mg/d)
2. Aggressive smoking cessation intervention
3. Target reductions of elevated blood pressure
4. Target reductions of lipid elevations, and 
5. Hyperglycemia reduced to target A_1C values in patients with T2DM

Is the ABI worth the diagnostic and therapeutic efforts? In the Edinburgh Artery Study (5 years’ duration),^1,3 persons with an ABI of 0.9 or lower had a 2.67 greater incidence of cardiovascular death. In a meta-analysis that included 44,590 people from 11 studies,^1,4 an ABI of less than 0.9 conferred a relative risk for CV death of 1.96. A recent study⁵ focused on 9 biomarkers (including C-reactive protein and lipoprotein[a]) that when high were associated with a low ABI. Assessment of CV risk will evolve into a multiple-test, noninvasive biomarker approach (including ABI) to identify higher-risk individuals and then intensively treat them.
 
Primary care is the “front line” in the war against CV disease. We can choose specific targets and weapons after an ABI.

NB: For those who want additional information and explicit instructions on performance of ABI, Reference 1 below is an excellent practical clinical review and Reference 2 is a recent comprehensive summary statement.

References    
1. Kim ES, Wattanakit K, Gornik HL. Using the ankle-brachial index to diagnose peripheral artery disease and assess cardiovascular risk. Cleve Clin J Med. 2012;79:651-661.
2. Aboyans V, Criqui MH, Abraham P, et al. AHA Scientific Statement: Measurement & Interpretation of the Ankle-Brachial Index. Circulation. 2012;126:2890-2909.
3. Leng GC, Lee AJ, Fowkes FG, et al. Incidence, natural history, and cardiovascular events in symptomatic and asymptomatic peripheral arterial disease in the general population. Int J Epidemiol. 1996;25:1172-1181.
4. Heald CL, Fowkes FG, Murray GD, et al. Risk of mortality and cardiovascular disease associated with the ankle-brachial index. Systematic Review. Atherosclerosis. 2006;189:61-69.
5. Ye Z, Ali Z, Klee GG. Associations of candidate biomarkers of vascular disease with ankle-brachial index and peripheral arterial disease. Am J Hypertens. 2013;26:495-502.