CT Scans Can Spot Blocked Arteries
WEDNESDAY Nov. 26, 2008 -- Expensive, high-tech CT devices that produce 64-slice images of arteries are almost, but not quite, as good as the standard method of detecting and gauging blood vessel blockages, a study finds.
Therefore, "multidetector CT angiography cannot replace conventional coronary angiography at present," concludes a report in the Nov. 27 issue of the New England Journal of Medicine.
But if that is so, experts ask, why is Medicare continuing to pay for these pricey CT exams?
"There is no evidence that they are of benefit to patients," said Dr. Rita F. Redberg, professor of medicine at the University of California, San Francisco, co-author of an editorial in the journal. "In general, there should be evidence of benefit before there is widespread use," she said.
Nevertheless, the study's lead author said the scans may have a place in cardiovascular care.
"Our study shows they do have value, because they have a high degree of diagnostic accuracy to identify patients with tight heart blockages," said Dr. Julie M. Miller, assistant professor of medicine at Johns Hopkins University. "Having the scan is a noninvasive procedure, and that is very attractive. Patients do not undergo the risk, even though it is small, of angiography."
Angiography, which requires insertion of a slim catheter tube into the blood vessels, is the typical way physicians gauge the degree of artery blockage to determine whether treatment is necessary. "Our paper shows for the first time that 64-CT scans can identify patients who need to go on to angioplasty and bypass procedures," Miller said. "It has diagnostic accuracy compared to other tests, such as stress testing. They create more invasive catheterizations than are needed than if the 64-CT test is used."
The study of 291 people with suspected coronary artery blockages was done at nine U.S. medical centers. They underwent both 64-CT and conventional coronary angiography.
The CT scans accurately predicted 84 percent of the treatment procedures that were required, compared to 82 percent accuracy for angiography.
"Until now, there has been doubt about 16-row or 64-row CT scanners being able to diagnose coronary disease," Miller said. The new study dispels that doubt, she said.
But there is no evidence that using a 64-CT scan changes the outcome, Redberg countered. "We need to have a study that uses CT and the traditional strategy and look at the outcome in the two arms to see which is better," she said.
This is more than an argument between academics. Aside from the health of people who might have CT scans, a great deal of money is involved. Redberg's editorial tells a tangled story of how the national Medicare program first declined coverage of the CT scans, asserting at the time that the "evidence is inadequate" to prove their value. However, a series of local decisions means Medicare now covers the scans in every state.
In fact, "the use of cardiac imaging has been increasing by 26 percent per year, despite a lack of evidence of outcome benefit," the editorial said. "Without such evidence, a high-resolution CT angiographic CT image of the heart is just another pretty picture," the expert said.
CT scans also expose patients to a relatively high dose of radiation, the editorial noted, citing a study which estimates that 1.5 percent to 2 percent of all U.S. cancer cases may be attributed to CT radiation.
However, Miller believes that CT scans do have a role in diagnosis.
"The cost to patients is generally reasonable when compared to other noninvasive imaging tests and cheaper than catheterization in general," she said. CT scans of the heart can be considered "for someone complaining of angina [chest pain] who needs further noninvasive evaluation, instead of a stress test, or patients who have had a previous stress test where the results were not clear."
There's more on coronary angiography at the U.S. National Library of Medicine.
Posted: November 2008