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Ultrasound Technique Can Spot Early Signs of Peripheral Arterial Disease

PORTLAND, Ore -- July 22 2008 -- Researchers have devised an ultrasound imaging technique that picks up subtle early evidence of peripheral arterial disease (PAD) that current conventional tests miss. The findings are published in the J Am Coll Cardiol Img.

The test, if approved for clinical use, could lead to early treatments that would head off the serious complications that can result from the disease.

According to background information from the study, cardiologists can noninvasively detect early signs of heart disease by imaging blood flows during exercise stress tests, but no equivalent stress test has been available for PAD.

Jonathan R. Lindner, MD, Oregon Health and Science University School of Medicine, Portland, Oregon, and colleagues, devised such a test for use in a study involving 26 control subjects with no history of coronary disease, hypertension or diabetes, and 39 patients with symptomatic PAD, of whom 19 had type 2 diabetes.

Lipid-shelled microbubbles were injected intravenously as an ultrasound contrast agent to evaluate microvascular blood flow in the calf muscles of subjects' legs at rest and during exercise. The results from blood flow imaging were compared with those from the most commonly used non-invasive diagnostic tests.

We found that contrast-enhanced ultrasound imaging outperformed most conventional forms of diagnostics in measuring and evaluating impairment in a patient's ability to recruit blood flow in the legs during modest exercise," said Dr. Lindner.

Specifically, the study found that patients with PAD had lower microvascular blood flow in their calf muscles than control subjects did after 2 minutes of plantar-flexion exercise.

"Peripheral arterial disease is becoming a huge problem because of the aging of the population and the increasing incidence of diabetes," said Dr. Lindner. "But we don't have good diagnostics for it, partly because a lot of the methods we have are based on measuring what's going on in the big vessels, the arteries and veins."

"PAD is a complex, very diffuse disease, which often involves functional abnormalities in the microcirculation system, the tiniest small vessels that go into muscle, bone, skin and connective tissues. How well the microcirculation system is functioning is what determines how well tissue is getting fed, which is the critical issue."

"The real benefit of a test like this -- which only takes about 5 minutes to do and doesn't require anything beyond the equipment and capabilities already in place in most vascular laboratories -- is their value for selecting the right therapies," said Dr. Lindner.

Further studies are needed on subjects for whom no diagnosis has yet been made. The technique does require additional training in how to receive the microbubble signals, said Lindner, but otherwise there are few significant hurdles yet to be cleared for the test to be used in vascular clinics everywhere.

SOURCE: Oregon Health and Science University School of Medicine

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