Mary McGrae McDermott, MD
Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M13-1561.
Requests for Single Reprints: Mary McGrae McDermott, MD, Department of Medicine, Feinberg School of Medicine, Northwestern University, 750 North Lake Shore Drive, 10th Floor, Chicago, IL 60611.
McDermott MM. Ankle–Brachial Index Screening to Improve Health Outcomes: Where Is the Evidence?. Ann Intern Med. 2013;159:362-363. doi: 10.7326/0003-4819-159-5-201309030-00012
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Published: Ann Intern Med. 2013;159(5):362-363.
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Dr Kirti Kain
Senior Lecturer, University of Leeds
September 12, 2013
Absolute systolic ankle blood pressures versus ankle brachial index
With reference to the editorial by McDermott it might be a global imperative to conduct ‘A definitive randomized, controlled trial to determine whether absolute systolic ankle blood pressures screening independent of systolic brachial blood pressures improves health outcomes in persons at risk for peripheral arterial disease and cardiovascular disease. Peripheral arterial disease can be defined by abnormally low and high ankle brachial index and both increase cardiovascular mortality. Majority of studies have defined peripheral arterial disease with ankle brachial index < 0.9. Ankle brachial index does not discriminate between the independent predictive values of systolic ankle blood pressures and systolic brachial blood pressures and these might be different in different populations.
Although the benefits of screening for, and treating, high blood pressure in adults is established, U.S. Preventive Services Task Force screening recommendations based on threshold of systolic brachial blood pressures results in missing more than half of those who have undiagnosed diabetes (1) . Increased systolic ankle blood pressures are associated with diabetes and higher hazard-ratios for fatal and non-fatal cardiovascular events in Europeans (2;3).
South Asians (more than a billion globally) continue to have increasing rates of visceral obesity, diabetes and cardiovascular mortality at a younger age but the prevalence of hypertension and its association with cardiovascular disease is not significantly different to Europeans. It is known that prevalence of ABI < 0.9 is lower even in subjects with diabetes in south Asians but systolic ankle blood pressures increase with diabetes and this increase along with association with cardiovascular disease is greater in South Asians when compared to Europeans (4). Therefore, in certain populations’ value of increased systolic ankle blood pressures (as one of the earliest signs of subclinical atherosclerosis) might be greater than increased systolic brachial blood pressures at a relatively younger age with short lifetime exposure to risk factors.
If predictive value of increased absolute high systolic ankle blood pressures for diabetes and cardiovascular disease in South Asian population is confirmed then possibly they can be used as a non-invasive, cheap and simple primary prevention screening tool for apparently healthy South Asians to reduce cardiovascular morbidity and mortality. Chronic diseases have increasing public health implications globally and focus ought to be on prevention more so when faced with hard economic times. Moreover, the developing countries have to deal with expense of managing infectious diseases and complications of chronic diseases.
There are no conflicts of interest.
(1) Casagrande SS, Cowie CC, Fradkin JE. Utility of the u.s. Preventive services task force criteria for diabetes screening. Am J Prev Med 2013; 45(2):167-174.
(2) Hietanen H, Paakkonen R, Salomaa V. Ankle and exercise blood pressures as predictors of coronary morbidity and mortality in a prospective follow-up study. J Hum Hypertens 2010; 24(9):577-584.
(3) Sutton-Tyrrell K, Venkitachalam L, Kanaya AM, Boudreau R, Harris T, Thompson T et al. Relationship of ankle blood pressures to cardiovascular events in older adults. Stroke 2008; 39(3):863-869.
(4) Kain K, Brockway M, Ishfaq T, Merrick M, Mahmood H, Ingoe JC et al. Ankle pressures in UK South Asians with diabetes mellitus: a case control study. Heart 2013; 99(9):614-619.
Mary McGrae McDermott, MD
November 7, 2013
First, Dr. Kain expresses concern that the ankle brachial index (ABI), a ratio of Doppler-recorded systolic pressures in the ankle and brachial arteries, does not distinguish between the independent predictive values of the systolic ankle and the systolic brachial blood pressure. But because the ABI calculation requires measurement of both the ankle and the brachial systolic pressures, prior prospective studies relating the ABI to subsequent cardiovascular events and mortality have the ability to separately analyze the independent predictive value of the systolic ankle and brachial blood pressures for cardiovascular events and mortality. For example, a meta-analysis relating the ABI to cardiovascular events and mortality included 16 prospective studies, 48,295 participants, and 480,325 person years of follow-up (1). This meta-analysis alone provides a robust opportunity to evaluate the relative independent associations of the ABI, ankle systolic pressure, and brachial systolic pressure with cardiovascular events and mortality. Second, Dr. Kain states that systolic blood pressure screening fails to identify more than half of individuals with undiagnosed diabetes. He implies that measuring the ankle systolic pressure may identify a greater number of individuals with undiagnosed diabetes. While Dr. Kain may be correct that an elevated ankle systolic pressure is more sensitive for identifying diabetes than an elevated brachial systolic pressure, neither test is likely to achieve optimal sensitivity as a diagnostic test for diabetes. For example, in the Multi-Ethnic Study of Atherosclerosis (MESA), most of the men and women with diabetes mellitus did not have an ABI > 1.30, consistent with a high ankle pressure. Although further study is needed, these and other data suggest that most people with diabetes mellitus do not have an elevated ankle pressure (2,3). Third, given the high rate of diabetes and cardiovascular disease in South Asians (4), early diagnosis, treatment, and prevention of diabetes and cardiovascular disease in South Asians are public health imperatives. However, in 2013, relatively little is known about the utility of screening systolic ankle blood pressures for identifying individuals at high risk of cardiovascular events and preventing adverse outcomes. The study by Kain et al supporting the hypothesis that elevated ankle pressures may be useful for diagnosing diabetes and cardiovascular disease in South Asians (5) employs a case-control study design, a relatively weak study design. Further study, including longitudinal prospective studies and randomized trials, is needed before large-scale screening with ankle systolic pressures in high-risk groups, such as South Asians, can be recommended. 1. Ankle Brachial Index Collaboration. Ankle brachial Index Combined with Framingham Risk Score to Predict Cardiovascular Events and Mortality. JAMA 2008;300:197-208. 2. McDermott MM, Liu K Criqui MH et al. Ankle-brachial index and subclinical cardiac and carotid disease: The Multi-Ethnic Study of Atherosclerosis. Am J Epidemiol 2005;162:33-41.3. Sutton-Tyrrell K, Venkitachalam L, Kanaya AM, et al. Relationship of ankle blood pressures to cardiovascular events in older adults. Stroke 2008;39:863-869.4. Tillin T, Hughes AD, Mayet J et al. The relationship between metabolic risk factors and incident cardiovascular disease in Europeans, South Asians, and African Caribbean. J Am Coll Cardiol 2013;61:1777-1786.5. Kain K, Brockway M, Ishfaq T et al. Ankle pressures in UK South Asians with diabetes mellitus: A case control study. Heart 2013;99:614-619.
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