PERIPHERAL ARTERY DISEASE (PAD)

The ankle-brachial index (ABI) is considered the primary diagnostic test for PAD. An ABI < 0.9 is up to 95% sensitive and 99% specific for the detection of angiographically confirmed PAD [19]. A simple ABI test can be performed in the office setting, using a hand-held Doppler device (5- or 10-MHz) with acoustic gel and appropriately sized (10-12 cm) blood pressure cuffs. With the patient resting in a supine position, the ABI is obtained by measuring the systolic pressure at the bilateral brachial, anterior tibial, and posterior tibial arteries. The ABI for each leg is calculated by dividing the higher of the two ankle systolic pressures by the higher of the two brachial pressures [20]. The ABI measurement technique is illustrated in FIGURE 1.

An ABI < 0.9 establishes the PAD diagnosis. The ABI is also considered an adequate measure of overall lower extremity perfusion and therefore can be readily used to quantify disease severity as shown in the table:

Limitations of the ABI:

• Medial arterial calcification resulting in non-compressible arteries may lead to false elevation (ABI > 1.4) or artificial normalization of ABI
• ABI may be normal or borderline at rest in patients with aortoiliac disease

In the case of normal resting ABIs in patients with a high clinical suspicion for PAD, an exercise ABI is helpful to establish the PAD diagnosis. Exercise ABI testing is performed in the vascular laboratory using a treadmill at a 12% grade at 1.5-2mph for at least 5 minutes with the goal of reproducing exertional leg symptoms. A 15-20% drop in the ABI following exercise is diagnostic of PAD. Exercise ABI testing is also useful for objective assessment of functional limitation in patients who report exertional leg symptoms.