Do we need lower extremity physiologic studies in the age of duplex scanners?

When clinical vascular laboratories appeared in the late 1960s, the concept of “nondestructive” or “noninvasive” testing was a novelty that was not widely accepted. The first vascular laboratory tests for the assessment of carotid, peripheral arterial, and venous disease were described as “indirect,” because they relied on detection of the physiologic alterations produced by vascular abnormalities.

These methods included the supraorbital Doppler examination and oculoplethysmography for carotid disease, ankle-brachial indices, segmental pressures, and pulse volume recordings for peripheral arterial disease, and the CW Doppler examination and impedance plethysmography for venous obstruction. In those early days, vascular testing was limited to some vascular surgery practices and physiology laboratories.

While these indirect physiologic tests were helpful for characterizing regional hemodynamics, they did not provide the detailed anatomic information on arterial lesions that vascular surgeons needed to plan treatment. It was not until direct ultrasound imaging of blood vessels became available in the late 1970s and early 1980s that interest in the non-invasive vascular laboratory increased. The “duplex concept” of combining B-mode imaging with Doppler flow detection appeared to overcome the major limitations of the indirect tests by providing two-dimensional images of an arterial lesion along with an assessment of the associated flow patterns – anatomy and hemodynamics – the best of both testing worlds.

The capabilities of duplex ultrasound were so impressive that direct duplex scanning rapidly replaced the indirect or physiologic tests for diagnosis of extracranial carotid disease and lower extremity deep venous thrombosis. But, as Thom points out, peripheral arterial disease is the only testing area in which physiologic studies are still considered as “primary” testing methods according to the IAC Standards and Guidelines for Vascular Testing Accreditation. So the challenge for the modern vascular laboratory is to determine which test to use and how to integrate physiologic testing and duplex scanning in the evaluation of patients with known or suspected peripheral arterial disease.

The clinical role of the vascular laboratory can be divided into the categories of screening, diagnosis, and follow-up. The merits of screening for peripheral arterial disease are beyond the scope of this debate, but screening tests must be safe, inexpensive, and capable of detecting the presence or absence of disease. Clearly, physiologic tests meet these requirements, and in most situations, an ankle-brachial index is all that is needed. Diagnostic testing in patients with signs and symptoms of peripheral arterial disease, including those that may be candidates for intervention, requires the specific anatomic and hemodynamic information that duplex scanning provides, but functional testing (i.e., treadmill exercise) can also be valuable in selected cases. Similarly, follow-up of peripheral arterial interventions usually requires duplex scanning to evaluate the anatomic and hemodynamic features of the treated arterial segment, while follow-up of documented but untreated peripheral arterial disease can often be accomplished primarily by physiologic tests alone.

Are lower-extremity physiologic studies no longer required in the age of modern duplex scanners? Although I am reluctant to admit it, strictly speaking, my friend, Thom, is correct when he responds with an emphatic “Wrong.” There is no reason to completely abandon the physiologic tests that have served us well since before the age of duplex scanning. A simple ankle-brachial index is easy to justify as part of almost any lower extremity arterial evaluation, and exercise treadmill testing is an excellent way to assess the functional status of a patient with peripheral arterial disease. However, vascular laboratories should consider how best to combine the use of physiologic testing and direct duplex imaging for peripheral arterial disease in order to avoid unnecessary or inappropriate testing. For most vascular laboratories, this means that initial screening should be done with physiologic tests, but the primary testing method for diagnosis and follow-up will be duplex scanning, supplemented by selective use of physiologic testing.

Dr. Zierler is professor of surgery at the University of Washington and medical director of the D.E. Strandness Jr. Vascular Laboratory at the University of Washington Medical Center and Harborview Medical Center, Seattle. He has no relevant conflicts.