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

Lower-Extremity Physiologic Studies Are No Longer Required – Wrong!

Okay Gene, consider an example from the cardiology world.

You walk up a flight of stairs and develop chest pain. Is it angina? If subsequent coronary catheterization reveals a 60% stenosis in your proximal right coronary artery, then you have an anatomic coronary lesion. But is this lesion causing angina? Maybe. If the catheter is pushed across the stenosis and a 12mm Hg resting pressure gradient is identified, the lesion also has hemodynamic significance. But is it causing angina? Possibly.

To clarify things, a functional study is necessary; specifically, you need to stress the heart (using treadmill exercise, biking, infusion of a catecholamine, etc.) and determine the subsequent cardiac response (pain, ECG changes, wall motion abnormalities, sestamibi/thallium uptake, etc.). If stress produces an abnormal cardiac response, does that mean you have angina? Probably.

Yes, it’s so simple a cardiologist can get it. Yet many vascular specialists seem to struggle with the concept that anatomic, hemodynamic, and functional tests provide different types of information about the arterial system. These tests are complimentary; when used properly they combine to yield information that no single test can provide. But the siren song of an image is hard to resist – after all, everyone loves pictures, and Duplex provides nice ones. With imaging, you can scan for aneurysms. You can see what plaque looks like. In some instances you can even perform operations or procedures solely on the basis of Duplex scanning. What more do you need? (Insert my sarcastic sneer here, Gene.)

Duplex even provides basic hemodynamic information about specific lesions (based on blood flow velocity changes across the lesion). However, it’s a mistake to think that hemodynamic changes across a particular lesion tell us much about the overall “hemodynamics” in a limb. Major arteries may be narrowed (or even completely occluded), but if the collateral vessels are good, the resulting hemodynamic compromise may be minimal. Unfortunately, Duplex scanning is relatively poor at identifying and assessing collateral flow. Tests like segmental pressures (and the ankle-brachial index, or ABI) often provide a better assessment of overall arterial status because the adequacy of collateral flow influences (and is reflected in) distal blood pressure measurements. It’s also naive to think that Duplex is the only means for noninvasively obtaining anatomic information about arterial disease; nonimaging tests using segmental pressures, multilevel pulse-volume recordings (PVRs), continuous-wave (CW) Doppler, etc. may not produce pretty pictures, but they can still localize arterial lesions to a particular anatomic level (aortoiliac vs. femoral-popliteal vs. infrapopliteal, etc.).

The combination of hemodynamic and functional testing is typically referred to as “physiologic” testing, but there’s much more to this than just CW Dopplerand pneumatic cuffs. Specific tests using Laser-Doppler to measure skin blood flow or microvascular perfusion pressure make it possible to (physiologically) assess the microcirculation. Transcutaneous Oxygen (TcPO2) measurement is available in many labs; this test provides valuable physiological information about skin viability and healing potential.

Where Duplex scanning meets its biggest challenge is in the area of functional testing. Yes, it’s possible to exercise the legs and identify subsequent flow (velocity) changes across certain lesions or vessels, but any seasoned sonographer knows that these studies are extremely difficult and time consuming. And because they typically can’t assess/account for collateral flow, they are often of questionable value for determining the adverse impact of arterial disease on the patient. In contrast, functional (exercise) studies performed with CW Doppler and air cuffs are simple, inexpensive, reliable, reproducible, and widely applicable.

Bottom line – physiologic studies are an indispensable part of noninvasive arterial testing and will certainly remain so. For any given patient, they are essential for identifying and quantifying the scope and impact of arterial disease. For populations, they are the test of choice for arterial screening. And, from a practical standpoint, they are required for IAC [intersocietal accreditation commission] laboratory accreditation in peripheral arterial testing (as you know, Duplex scanning is optional for arterial accreditation – but physiologic studies are mandatory!)

Finally, the same characteristics that make physiologic tests important for assessing arterial disease are equally – or perhaps even more – relevant for the assessment of venous disease, but the application of this approach remains in its infancy. It’s a good topic for another discussion.

Dr. Rooke is the Krehbiel Professor of Vascular Medicine at the Mayo Clinic, Rochester, Minn. He has no relevant conflicts.

Lower-Extremity Physiologic Studies Are No Longer Required – Yes ... Maybe!

My friend, Thom, makes a strong case for the value of physiologic studies in patients with lower extremity arterial disease – so strong, in fact, that one might wonder if there is any truly cogent “counterpoint” at all. To provide some perspective on this issue, let’s take a look back to see how this field started and consider why someone would even dare make the statement that is being debated here.