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Clinical assessment of patients with Peripheral Arterial Disease (PAD)
Peripheral artery disease (PAD) is often asymptomatic with only about half of all patients exhibiting typical symptoms, necessitating diagnosis through other means and tools. Several are currently in use, differing in the invasiveness for the patient and scope, making some more appropriate for specific groups of patients than others.
Standard clinical examination of individuals with suspected PAD can yield a wealth of pertinent information such as family history (those with relatives with PAD are at an increased risk) and inclusion in risk groups (e.g. smokers, who have significantly higher incidence of the disease), but has insufficient diagnostic value in itself [1, 2, 3]. Fortunately, there are several diagnostic methods which can yield accurate information about the presence and severity of the disease, but clinicians should exercise discrimination in their application and be cognisant of their advantages and limitations.
Methods of arterial assessment
Diagnostic methods for PAD generally fall in two distinct categories, which also dictate their appropriateness (cost, complexity) for specific purposes (single patients, large scale screening); invasive and non-invasive methods. The sole representative of invasive procedures is angiography (CT and MR, although in the latter case the procedure can be non-invasive), while the non-invasive ones are represented by physical examination (pulse palpation), Ankle-Brachial Index (ABI) measurement (two methods) and TBI (toe-brachial index) measurement.
Angiography
A medical imaging technique that entails the introduction of contrast medium in the patient’s bloodstream through a cannula ahead of X-ray (or MRI, although in that case the procedure is a bit different and can be done without the contrast medium) imaging of the area of interest (in this case the lower extremities). It is the most accurate method for diagnosing blood flow issues in the lower extremities, with very high detection, between 89 and 100%, and specificity in the 92 to 100% range [4, 5].
Angiographic arterial assessment of lower extremities, while highly accurate, is not without drawbacks. In case of CT angiography, the two major ones are exposure to high doses of ionising radiation and the potential for contrast-induced nephropathy (some patients with PAD also have renal dysfunction) [5, 6]. MR procedure is safer in both regards (if no contrast medium is used), but like CT angiography requires specialised personnel (radiologist, technicians) and equipment. Angiography, especially MRI, is therefore a fairly high cost procedure, limiting its usability for large scale screening of potential patients for PAD.
Physical examination (pulse palpation)
Diagnosing vascular health on the basis of pulse palpation is a well-established diagnostic method, but its accuracy and specificity are greatly predicated on the examiners (in)experience. This is especially true in diagnosis for PAD. Studies have shown that while this approach has notable diagnostic value when performed by a skilled vascular surgeon, it can lead to false positives when performed by untrained observers (e.g. general practitioners) [7].
Ankle-Brachial Index (ABI) measurement (Doppler probe)
The Doppler method involves the use of a sphygmomanometer and a Doppler wand (probe). The examiner places the inflatable cuff of the meter in the proximity of the brachial artery (upper arm) or posterior tibial artery and dorsalis pedis artery (lower leg, above the ankle) and starts inflating it until the pulse can no longer be detected with the Doppler wand in the examined artery. The pressure cuff is then slowly deflated until the pulse is re-detected with the wand at which point the measurement of systolic pressure is taken. The procedure is repeated on the remaining limbs and the ABI value is manually calculated.
This method, while accurate and reliable, has two major drawbacks. The first one is accuracy issues if the procedure is performed by an unskilled examiner [8] . The second one is the time-consuming aspect, since it can take up to 30 minutes to complete the procedure.
Ankle-Brachial Index (ABI) measurement (MESI ABPI MD®)
The plethysmography method of measuring ABI, on the other hand, has many advantages in comparison with the Doppler method, including the time-saving nature and simplicity of its execution, lending itself to the purpose of preventive screening of large numbers of patients for PAD. The MESI ABPI MD® for ABI measurement on the market, is, for example, completely automatic and does not require special or extensive training to operate.
It works on a different principle, utilising 3 blood pressure cuffs, which are placed on an arm and both legs and then automatically inflated and deflated to record the arterial pulse , which the machine then translates into ABI. This whole procedure takes only 1 minute. The only similarity with the Doppler method is the requirement to place the patient in a supine position.
Toe-Brachial Index (TBI) measurement
In some patients ABI measurement cannot be performed, i.e. the ABI value is uninterpretable (the value is higher than the median “healthy” ABI for individuals without PAD) due to incompressibility of the arteries (arterial calcification, common in individuals with diabetes and renal failure). The alternative, sans angiography, is the TBI measurement. The procedure is similar to the ABI measurement, but with the difference of taking the blood pressure measurement on the toe instead at the ankle.
This is done using a greatly miniaturised version of the blood pressure cuffs for the arms (with the addition of a photoplethysmograph sensor) which is placed on the toe. Another difference in comparison with ABI is the value of TBI, which is, in numerical terms, lower, but has the same correlation. The lower is TBI, the higher is the presence and severity of PAD.