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Heart Imaging Tool Under the Microscope

The death of newsman Tim Russert last month from a massive heart attack raised interest in new technologies that may better identify people at risk for life-threatening cardiac events.

A test that one expert calls "the iPod of medical imaging" is emerging as an important tool for visualizing plaque buildup in patients with known coronary artery disease.

But a new study offers little support for the use of computed tomography angiography (CTA) as an early screening tool for people with no symptoms of artery disease, such as chest pain or an abnormal stress test .

And researchers conclude that the safety of CTA must be established before the test can be recommended for the routine screening of people with no symptoms.

CTA-associated radiation exposure has been linked to an increase in the lifetime risk of cancer , especially in women and young people.

"CTA has promise, but at present we simply don't have the data to confirm its usefulness and safety in an asymptomatic population," study co-author Hyuk-Jae Chang, MD, PhD, of South Korea's Seoul National University Bundang Hospital, tells WebMD.

CTA-Detected Plaque

Also known as multislice computed tomography or 64-slice CT, CTA screening is being prematurely marketed to the public as a screening tool for low-risk populations, even though there are no guidelines recommending its use for this purpose, Chang says.

"Everyone wants the latest technology, and this is something like the iPod of medical imaging," says cardiologist Ann F. Bolger, MD, of the University of California, San Francisco. "Unfortunately, the technology is only as useful as the science behind it."

In one of the first studies to examine the value of CTA for identifying coronary artery disease in presumably low-risk populations, Chang and colleagues followed 1,000 asymptomatic people without established artery disease for about a year and a half following CTA screening.

Although the test did identify significant and severe plaque buildup in 5% and 2% of the people, respectively, the sample size was too small and the follow-up too short to determine the value of CTA screening in people without symptoms, Chang says.

The researchers plan to follow 5,000 asymptomatic patients for five years following CTA screening.

"We do not yet have the data to show that the risks outweigh the benefits in this population, but we also don't have the data to show that the benefits outweigh the risks," Chang says. "So we must wait."

Radiation Risk a Concern

One big problem with the test is that it is not clear what the findings mean in patients with few risk factors for heart disease , Bolger tells WebMD.

"If you don't see coronary disease, is that person off the hook, and if you do see it does that mean that the person will have a coronary event in a year, or two, or five?" she says. "We can't answer these questions yet."

This, combined with a cost of anywhere from $500 to $1,500 per scan, and the radiation risk identified in earlier studies, makes it too soon to recommend CTA for the routine screening of asymptomatic people, she says.

The American Heart Association came to the same conclusion in a recently published statement on the use of new noninvasive techniques to measure arterial plaque, finding that CTA should not be used to screen for coronary artery disease in people with no evidence of disease.

But Bolger says it is only a matter of time before researchers gain a better understanding of the role of CTA and other new-generation tests designed to identify people at risk for heart attacks and strokes.

"With every year that goes by our understanding about these tests and how to use them gets better," she says.

American Heart Association past president Robert Bonow, MD, agrees.

Bonow calls CTA "a very exciting technology," but he tells WebMD that its safey and effectiveness for identifying coronary artery disease in asymptomatic populations remains to be determined.

A professor of medicine at Northwestern University, Bonow is also the chief of cardiology at Northwestern Memorial Hospital.

"Other (new-generation) tests that involve much less radiation are showing a lot of promise, so we will just have to see," he says.

By Salynn Boyles
Reviewed by Brunilda Nazario
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