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ORIGINAL ARTICLE
Year : 2022  |  Volume : 9  |  Issue : 1  |  Page : 22-26

Utility of ankle brachial index in the diagnosis of peripheral arterial disease in a resource limited setting


1 Department of Radiodiagnosis, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India
2 CVTS, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir, India

Date of Submission12-Jun-2021
Date of Decision22-Jun-2021
Date of Acceptance05-Jul-2021
Date of Web Publication23-Mar-2022

Correspondence Address:
Arshed Hussain Parry
Department of Radiodiagnosis, Sher-i-Kashmir Institute of Medical Sciences, Srinagar, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijves.ijves_65_21

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  Abstract 


Background: Peripheral arterial disease (PAD) constitutes a significant healthcare problem with immense health and economic implications. Owing to ill-equipped healthcare systems in poor countries the diagnosis of PAD demands the availability of a reasonably reliable and inexpensive diagnostic test. Ankle brachial index (ABI) is a simple, inexpensive office-based test for the diagnosis of PAD. The study was aimed to evaluate the reliability of ABI for the diagnosis of PAD using Doppler ultrasound (DUS) as the gold standard. Methods: The ABI of patients suspected of having lower limb PAD was measured followed by DUS examination. The sensitivity and specificity of ABI for the diagnosis of PAD was calculated by comparing it with DUS which was used as the reference or standard diagnostic test. Results: The ABI of a total of 200 limbs from 100 patients was recorded followed by DUS examination. One hundred and thirty-two limbs (66%) had PAD on DUS which was graded as mild, moderate, and severe in 45.5%, 27.2% and 30.3% respectively. Out of 132 patients who had PAD on Doppler, 96/132 (72.8%) were correctly labelled as PAD on ABI, whereas 36/132 (27.2%) received an erroneous diagnosis of normal on ABI. Conversely, only 6/60 (10%) patients who were labelled as PAD on ABI had a normal arterial system on DUS. The ABI yielded a low overall sensitivity of 72.7% and a high specificity of 90%. The sensitivity was relatively low for mild PAD (52.7%), however, for moderate and severe PAD, ABI demonstrated a high sensitivity of 88.9% and 100% respectively. Overall agreement between ABI and DUS for the diagnosis of PAD was good (k = 0.67). Conclusion: ABI demonstrated a good sensitivity and specificity for the diagnosis of PAD especially in patients with moderate-severe PAD. Combined with the advantages of ready availability, low cost, and technical feasibility the use of ABI should be maximized in routine clinical practice to clinch the diagnosis of PAD in suspected individuals.

Keywords: Ankle brachial index, Doppler ultrasound, peripheral arterial disease


How to cite this article:
Bhat MH, Parry AH, Maqsood S, Ganie FA. Utility of ankle brachial index in the diagnosis of peripheral arterial disease in a resource limited setting. Indian J Vasc Endovasc Surg 2022;9:22-6

How to cite this URL:
Bhat MH, Parry AH, Maqsood S, Ganie FA. Utility of ankle brachial index in the diagnosis of peripheral arterial disease in a resource limited setting. Indian J Vasc Endovasc Surg [serial online] 2022 [cited 2022 Jul 1];9:22-6. Available from: https://www.indjvascsurg.org/text.asp?2022/9/1/22/340505




  Introduction Top


Peripheral arterial disease (PAD) refers to the partial or complete obstruction of arteries other than coronary arteries that results in impaired blood supply and ischemia.[1] Atherosclerosis is the leading cause of PAD where an atherosclerotic plaque causes mechanical obstruction to the flow of blood. PAD constitutes one of the important global health problems with significant economic burdens. It is estimated that over 230 million people around the world are suffering from PAD with approximately 20% having some degree of claudication.[2],[3] Lower limb PAD is uncommon before 50-years of age; however, its incidence rises steeply with increasing age and up to 13% of Western population aged over 50 are affected by this disease.[4] Most patients are asymptomatic, but many present with the classical manifestation of intermittent claudication (pain on walking which is relieved by rest). Severe reduction of blood flow to the limb results in pain on rest or tissue loss which is referred to critical limb ischaemia.[5] Given the systemic nature of atherosclerosis around 60% will have coronary artery disease and around 30% suffer from cerebrovascular disease.[6] Within 5 years of diagnosis, 10%–15% of patient who have claudication will demise from ischemic heart disease.[7],[8] Therefore, a proper management would entail identification and modification of the risk factors that lie at the core of the disease process.

Although digital subtraction angiography is the gold standard technique for the diagnosis of PAD but due to its invasive nature, use of contrast agent, radiation hazards, procedural risks, and the cost it has found limited usage and has been supplanted by computed tomographic angiography (CTA) or magnetic resonance angiography (MRA).[9],[10] CTA and MRA are exquisitely sensitive to the diagnosis of PAD, but their wide usage is restricted due to limited availability, need for contrast administration and prohibitive cost. Doppler ultrasound (DUS) has attained the status of primary diagnostic modality for the evaluation of patients suspected with PAD owing to lack of radiation exposure, lesser cost, easy availability with no associated procedural risks. DUS has a high sensitivity of 92% and specificity of 97% for the diagnosis of PAD.[11] As per the National Institute for Health and Care Excellence recommendation DUS should be used as the first line diagnostic test for patients suspected of having PAD and angiography should be reserved for patients who need further evaluation.[12] Notwithstanding the advantages of DUS its use in routine clinical practice is hindered by the need for a specialised ultrasound equipment, need of trained sonologist or radiologist and higher cost. This problem is even more significant in the limited resource settings especially in poor and developing countries which have ill-equipped healthcare systems.[13],[14]

The ankle brachial index (ABI) is the ratio of the highest systolic blood pressure measured at the ankle to the highest systolic pressure measured at the brachial artery.[14] It is a simple test which uses an inexpensive equipment and has the advantages of easy availability, cost-effectiveness, and reproducibility.[14],[15] Due to these advantages, it is an attractive modality for office-based diagnosis of PAD at the primary health care level. The present study was aimed to evaluate the utility of ABI in the diagnosis of PAD by comparing it with DUS.


  Methods Top


Study design and patient cohort

This was a single-centre prospective study covering a 2-year study period. The study was approved by Institutional Ethical Committee of our institution and informed consent was obtained from each patient. Patients who presented with clinical suspicion of lower limb PAD were enrolled in the study. Patients presenting with intermittent claudication defined as calf or thigh pain brought about by exertion and relieved by rest with or without diminished or absent peripheral pulses (posterior tibial or dorsalis pedis) were suspected of having PAD and enrolled prospectively in the study.

Data collection

After obtaining a detailed history and clinical examination relevant investigations like lipid profile, blood sugars were recorded. Patients with a positive history of claudication or suspected vascular insufficiency on clinical assessment were subjected to further assessment with ABI and DUS. The DUS was performed within 10-days of ABI measurement.

Ankle brachial index measurement

The systolic blood pressure was measured in both brachial arteries using standard sized sphygmomanometer and a 7.5 MHz Doppler ultrasound (DUS) probe with patient in supine position after a rest of at least 15-min. Similarly, systolic blood pressure was measured at ankle in dorsalis pedis and posterior tibial arteries. The ratio of highest systolic blood pressure at ankle to that at brachial artery was used to calculate the ABI. ABI was calculated separately for each leg. An ABI <0.9 was regarded as PAD whereas, ABI in the range of 0.9–1.3 was considered as normal according to international guidelines.[16],[17] An ABI >1.3 was deemed to be the result of stiff and incompressible vessels and were excluded from final analysis.

Doppler assessment

DUS of each lower limb arterial system was done using TOSHIBA XARIO ultrasound scanner (Toshiba, Japan) with 7.5 MHz linear array transducer. Both colour Doppler imaging and duplex Doppler examinations were performed with appropriate control settings. Common femoral, profunda femoris, superficial femoral and anterior tibial arteries were scanned with patient in supine position while popliteal, posterior tibial and peroneal arteries were scanned in a decubitus position. The aorto-iliac segments were examined using 3.5 MHz curvilinear probe in those cases where femoral artery waveform suggested a significant proximal disease. The arteries were first assessed on B-mode for diameter and luminal narrowing followed by colour Doppler assessment. Duplex ultrasound was used to measure flow velocity. Peak systolic velocity (PSV) was measured in centimetre per second (cm/s). A diagnosis of PAD was invoked when there was at least a reduction of ≥50% in the luminal diameter or PSV ≥150 cm/s. Arterial stenosis was graded as mild when vessel diameter was reduced by 50%–75% or PSV of 200–300 cm/s, moderate when vessel diameter was reduced by 76%–99% or PSV >300 cm/s. When the vessel was completely occluded, it was referred to as severe stenosis.[18],[19]

Statistical analysis

Data were analysed using the Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL, USA, version 22.0). All the categorical variables were shown in the form of frequency and percentage and continuous variables were represented as means and standard deviations. The sensitivity, specificity of ABI for the diagnosis of PAD was measured after comparing it with DUS which was used as the reference or standard diagnostic test. Agreement between ABI and DUS was tested by Cohen's Kappa (κ) test. The level of agreement was classified as perfect agreement (κ =1), excellent agreement (κ =0.8–0.99), good agreement (κ =0.6–0.79), moderate agreement (κ =0.4–0.59) and poor agreement (κ = <0.4).


  Results Top


Among the study cohort of 100 patients, 88 (88%) were males and 12 (12%) were females with a sex ratio of 7.3:1. Majority of patients were in the age group of 50–70 years. Smoking was the commonest risk factor followed by hypertension and dyslipidemia. The various demographic characteristics and clinical features of the study population are presented in [Table 1].
Table 1: Demographic profile and clinical features of the study cohort

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Out of total 200 limbs in 100 patients, 8 limbs had dense calcifications with ABI >1.3 and were excluded from final analysis while calculating sensitivity and specificity of ABI. One hundred and thirty-two limbs (66%) had PAD on DUS which was graded as mild, moderate, and severe in 45.5%, 27.2% and 30.3% respectively. Of the 132 limbs diagnosed as PAD on DUS, only 92 were categorized as PAD by ABI, yielding a sensitivity of 72.7%. Out of the 60 limbs classified as normal on DUS, 54 limbs were correctly categorized as normal based on ABI yielding a specificity of 90% [Table 2]. In the present study, out of the 14 patients who had an ABI range of 0.9–0.7, 9 (64%) were completely asymptomatic with no clinical or examination findings of PAD.
Table 2: Comparison between ankle brachial index and doppler ultrasound

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The ABI value <0.40 showed 100% agreement with DUS, ABI of 0.40-0.69 showed 94.1% agreement and ABI of 0.70–0.90 showed 85.7% agreement. ABPI of >0.9 (negative for PAD) showed 60% agreement with DUS. Overall agreement was 78.1% (κ =0.65; good agreement) [Table 3].
Table 3: Agreement between ankle brachial index and doppler ultrasound

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  Discussion Top


DUS, CTA and MRA are extremely sensitive and specific diagnostic tools for identifying PAD. However, all these modalities require costly equipment and skilled manpower thus these tools are not readily available.[1],[2] This problem is even more significant in poor countries with limited resources. However, the statistics reveal that the prevalence of PAD is on the rise in these countries due to increased prevalence of diabetes, obesity, and hypertension. This calls for identification of a simple, inexpensive but reasonably reliable diagnostic tool that can be readily used in these resource constrained settings.[14] The ABI is a simple, cheap, and office-based test which requires minimal expertise to perform. American Diabetes Association recommends that ABI measurements should be performed in all diabetic patients older than 50 years old and those who present symptoms of PAD.[20]

The results of the present study demonstrate the reliability of ABI as a diagnostic tool in the evaluation of patients suspected of having PAD. ABI demonstrated a good sensitivity and specificity especially in the moderate and severe PAD patients. However, owing to a relatively low sensitivity in the mild PAD, ABI could potentially miss some patients of PAD when used as a screening test. So, this calls for caution in the mild PAD patients where if the clinical suspicion of PAD is high a second confirmatory test like DUS should be undertaken. However, when a patient is labelled as PAD on ABI it is almost certain that he will have PAD on DUS. As per the updated guidelines of National Institute for Health and Care Excellence the diagnosis of PAD should not be ruled out solely based on a normal ABI especially in diabetic population who are at a higher risk of vascular calcification and may have spuriously high ankle pressures.[12] However, the findings of the present study do not necessarily conform to this view especially in moderate-severe PAD where ABI has an excellent sensitivity. Our findings corroborate other data which has reported a reasonably high accuracy of ABI in the diagnosis of PAD.[14],[21],[22]

Alnaeb et al.[23] demonstrated the accuracy of ABI in diabetic patients and reported a high sensitivity of 80% and specificity of 93% compared to Doppler. Another study by Ugwu et al.[14] in diabetic people recorded a high diagnostic accuracy of over 90% for ABI. In non-diabetics ABI has demonstrated a good diagnostic accuracy in comparison with DUS and angiography.[21],[22]

In the present study, ABI demonstrated a relatively low sensitivity in patients with mild disease compared to DUS which would fail to diagnose these cases. Therefore, in this subset of patients a strong clinical suspicion of PAD warrants the use of other diagnostic modalities like DUS to clinch the diagnosis of PAD. However, in patients with moderate to severe disease, ABI demonstrated a high sensitivity and specificity reaching a sensitivity of 100% in subjects with severe PAD.

2016 clinical practice guidelines report of the American College of Cardiology/American Heart Association task force recommends performance of ABI in all at risk patients with history or physical examination findings suggestive of PAD to establish the diagnosis with a class of recommendation (COR) I. Duplex ultrasound is recommended to localise the anatomical segments of diseased vessels (i. e., aortoiliac, femoropopliteal or infrapopliteal) to plan management. In patients with increased risk of PAD but without history or physical examination findings of PAD measurement of ABI is a reasonable strategy with COR of IIa. This is based on the premise that patients with no historical or examination evidence of PAD but with an abnormal ABI have a poorer cardiovascular morbidity and mortality outcomes compared to the patients with normal ABI. Also, patients with a low ABI have a poorer functional status and demonstrate a faster decline than do patients with normal ABI.

The same task force report also categorises Duplex, CTA and MRA under COR I for anatomical segment localization in symptomatic PAD patients in whom revascularization is considered.[24]

In the present study, out of the 14 patients who had an ABI range of 0.9–0.7, 9 (64%) were completely asymptomatic with no clinical or examination findings of PAD. These patients had normal palpable DPA/PTA pulses at ankle. However, none of the patients with an ABI of < 0.7 was asymptomatic for PAD. Thus, measurement of ABI will detect PAD in asymptomatic individuals and alter management. ABI may also obviate the need for DUS in patients with mild PAD (ABI 0.9–0.7) as this subset of patients is expected to demonstrate mild disease on DUS and thus DUS may not necessarily change the management in these patients. ABI is an integral part of initial exam and in present practice has a role in surveillance of patients who are having non-reconstructible PAD on best medical therapy. ABI also has a role to assess clinical improvement post re-vascularisation.

DUS is still not widely available at the primary health care level especially in rural India. This problem is further complicated by the dearth of trained manpower (sonologist or radiologist) needed to perform DUS. The burgeoning diabetic population, rising obesity and hypertension in India would also lead to an expected surge in PAD. The need for a simple and readily available tool is thus essential to cater to the rising population of PAD. This underlines the role of ABI in such resource constrained settings. ABI can help triage patients and allow us to select patients in need of DUS with patients of moderate-severe disease detected on ABI referred for DUS.

ABI has certain limitations. It gives false negative results in patients with dense atherosclerotic calcifications when the arteries are stiff and incompressible. It does not identify the exact location of stenosis. It may be time consuming and technically difficult to perform in individuals with leg edema.

The study has some limitations. Single centre design and a small number of patients is an important limitation.


  Conclusion Top


ABI is a cheap and reasonably accurate tool for the evaluation of patients suspected of having PAD. It demonstrates high sensitivity and specificity especially in the moderate and severe PAD patients. However, the sensitivity is limited in mild PAD which must be borne in mind while evaluating these patients. Taking this limitation of ABI into account, the potential of this simple, cheap, and noninvasive test must be fully utilised especially in recourse constrained countries where, cross-sectional imaging modalities, are not widely available.

Acknowledgements

The authors are grateful to the Department of CVTS for their support throughout.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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