No, says Charalambos Vlachopoulos, Athens Medical School, Athens, GreeceYes, says Katerina K Naka, University of Ioannina Medical School, Ioannina, Greece
Screening for occult disease in the general population holds the promise of early detection and therapy. Nonetheless, because no test is perfect, screening is hampered by false-positives, which leads to unwarranted treatment and testing. According to the Bayes’ theorem, post-test probability is a function of pretest probability (or disease prevalence) and the likelihood ratio of the test (ie, its diagnostic accuracy). Conceivably, if the disease is very rare or very frequent, and if our diagnostic tools are not accurate, then screening can be misleading.
The prevalence of PAD differs according to the vascular bed. The most common form is lower extremity artery disease (LEAD); its frequency is strongly age-related, being uncommon before 50 years and rising steeply at older ages.
Moreover, women are less likely to have LEAD. In the Framingham Study, the incidence of intermittent claudication was 0.4 per 1000 aged 35-45 years and six per 1000 aged 65 years and older; female incidence was around half that in men, but more similar at other ages. The presence of PAD in renal, mesenteric and upper extremity arteries is similarly low.
The tools for the detection of PAD include the ankle-brachial index (ABI), carotid ultrasonography, CT and MR angiography. ABI is solely used for the detection of LEAD; a threshold of 0.9 is used for diagnosis, but it is unclear if higher thresholds can be used to detect earlier, subclinical disease. Moreover, calcified vessels can lead to falsely high ABI values.
Carotid ultrasonogaphy can be used for the measurement of intima-media thickness (IMT) and the detection of plaques. Meta-analysed data from 45,828 individuals showed that common IMT measurements do not add significantly to the Framingham Risk Score for prediction of first myocardial infarction or stroke. The detection of carotid plaque has a superior diagnostic accuracy, although data are derived from smaller, mostly Caucasian cohorts and should be used with care. CT and MR angiography have a favorable profile for detecting PAD, but are hampered by radiation exposure and limited availability. Taken together, the aforementioned data on disease prevalence and characteristics of available screening modalities speak against the widespread screening for PAD.
An additional argument against screening the general population is that treatments greatly overlap with those for CAD, and are targeted in the modification of the common underlying risk factors with the inclusion of antithrombotic agents. Thus, and because PAD and CAD frequently coexist, a logical inference is that screening for CAD should precede screening for PAD and therapy superseded by treatment for CAD.
In conclusion, screening for PAD should not be performed in the general population, but reserved for selected populations considered at high risk for CVD. Acknowledgment of the strengths and weaknesses of different screening modalities will facilitate the interpretation of results and guide therapy.
PAD is a prevalent and serious disease, more commonly found in lower extremity arteries - though carotid and other arteries may also be affected. Up to 10% of people aged <70 years and 15-20% >70 years have PAD.
PAD is a marker of extensive atherosclerosis and is independently associated with increased risks of vascular events and death. Subjects with PAD, even asymptomatic, are at high cardiovascular risk (equivalent to CAD) and are thus recommended for treatment. However, as up to 75% of PAD patients are asymptomatic, PAD is frequently under-diagnosed and under-treated.
In subjects without known CVD, a diagnosis of PAD, regardless of symptoms, requires treatment beyond general advice on lifestyle. This may include statins, antihypertensives and antiplatelet agents in most patients. The diagnosis of PAD is also associated with a poor prognosis in those with other known CVD, both stable and acute.
A careful medical history and detailed physical examination are two important tools in screening for PAD. In addition to CVD risk factors and co-morbidities, all types of symptoms suggesting disease in any vascular bed should be systematically looked for, although these are frequently absent or atypical. The cardiovascular examination should include palpation and auscultation of all relevant arteries, inspection of the feet, and note of the colour, temperature, quality of skin and hair, and presence of ulcerations or poorly healing wounds in the extremities. Carotid, abdominal or femoral bruits, pulse abnormalities in lower extremities, or inter-arm BP difference >20 mmHg are indicative of vascular disease.
A non-invasive screening procedure for PAD is the ankle-brachial index (ABI), calculated as the ratio of the ankle to brachial systolic BP and normal values range from 1.1 to 1.3. ABI values <0.9 indicate the presence of flow-limiting stenosis, while supranormal values (>1.4) are associated with medial calcification, often found in diabetes and chronic kidney disease. ABI is a reliable diagnostic tool for PAD with a 90% sensitivity and specificity compared with angiography and a strong marker for CVD. ABI can be measured easily, rapidly, non-invasively, safely and at very low cost may identify a large number of patients with previously unrecognised PAD.
Although no RCT evidence on screening for PAD exists, several guidelines have endorsed the use of ABI in risk assessment. The European guidelines for CVD prevention recommend ABI for detecting PAD in intermediate risk individuals (class IIa/B), similar to the ESH/ESC guidelines for hypertension. According to the ESC/EASD guidelines for diabetes, ABI may be considered a useful marker that adds predictive value to the usual risk estimate. The latest ACC/AHA guidelines recommend that ABI may be considered if, after quantitative risk assessment, a risk-based treatment decision is uncertain (class IIb/B). In the recent position paper from the ESC Working Group on Peripheral Circulation, ABI is recommended as a useful vascular biomarker for risk stratification in primary and secondary prevention (IIa/A).
The incidence of asymptomatic, under-diagnosed and under-treated PAD is high despite its association with a significantly increased risk for cardiovascular events. Thus, screening for PAD, especially among subjects considered to be at intermediate cardiovascular risk, using the non-invasive, widely available, easy-to-use and low-cost ABI, could have a beneficial impact on public health. The (cost-)effectiveness of such a screening intervention to guide decision-making in the prevention of cardiovascular events needs to be confirmed in the future.
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