By Anne Harding
WEDNESDAY, Nov. 26, 2008 (Health.com) — An expensive CT scan that uses multiple X-rays to produce spectacular 3–D images of the heart can’t replace tried-and-true coronary angiography for finding blocked blood vessels in chest-pain patients, according to a study in the New England Journal of Medicine.
But doctors are using the newer test—sometimes because patients ask for it—despite a lack of evidence that it’s helpful, and a possibility that it might be harmful.
“I think it’s being used without clear data of any benefit for the patient,” says Rita Redberg, MD, a professor at the University of California at San Francisco School of Medicine, who wrote an article accompanying the study.
The gold standard for diagnosing heart disease is coronary angiography (also known as an angiogram or cardiac catheterization), in which doctors snake a tube through the femoral artery in the leg and up into heart vessels to release a dye that lights up blockages on an X-ray.
CT scans of the heart, known as multi-detector computed tomographic (CT) angiography, are less invasive than angiograms. But the CT scans use a contrast dye and multiple radiation-generating X-rays, which a computer assembles into a high-resolution, three-dimensional image of the heart.
Supporters of the CT scans say they could be used in patients with chest pain who are at lower risk of having heart disease due to their age, sex, or type of pain. If the test doesn’t find blockages, they say, these patients could skip traditional angiography altogether.
However, in the new study, Julie M. Miller, MD, of Johns Hopkins University School of Medicine in Baltimore, and her colleagues looked at 291 patients who were scheduled for an angiogram but also had a 64-slice CT scan. They found the newer test was less accurate and yielded more false negatives than previous single-center studies had suggested.
Robert Bonow, MD, chief of cardiology at Northwestern University’s Feinberg School of Medicine, notes that about 10% of study participants with a positive test had normal coronary arteries, and 17% of those with a normal test had coronary disease.
Meanwhile, Medicare has covered the CT scans since 2006, and the tests are in widespread use, even though their usefulness for patients is unclear. The CT scans cost about $700 and angiograms cost about $1,500, according to Johns Hopkins. However, people who have the CT scans often end up needing the angiogram anyway.
Dr. Bonow says he expects the new findings could “put the brakes” on current enthusiasm for the test. “It is the way the world’s going to evolve in the future, but I just don’t think we’re there yet," he says.
While traditional angiography is invasive, he adds, the risks are exceedingly low when performed by an experienced clinician. And if the test does identify blockages in the heart’s arteries, they can be treated with stents or angioplasty right away. (Both require a catheter threaded through an artery into the heart.)
In the United States, 30% of angiograms find no blockages in the heart arteries, notes Kim Allan Williams, MD, a professor of medicine and radiology at the University of Chicago. “We’d like to fix it so we have no more normal angiograms,” he says.
According to Dr. Williams, CT angiography is useful for ruling out heart disease in patients with active chest pain and equivocal stress test results. (In a stress test, patients’ hearts are monitored while they exercise.)
“It does help you select the patients who are going to need further management with revascularization and that’s really what you want the test to do,” Dr. Williams says. Revascularization is any procedure that restores blood flow to the heart, such as bypass surgery or angioplasty.
But Dr. Redberg argues that the usefulness of a CT scan in patients with chest pain is debatable and the test has risks. The scan exposes patients to considerably more radiation than an angiogram, she says, and these patients may wind up needing an angiogram anyway—as well as other tests that could expose them to even more radiation, like those that use nuclear tracers.
“Importantly, but unfortunately, we don’t know what the radiation risks are,” Dr. Redberg says. “It’s been estimated that we’re going to see tens of thousands of additional cancers in the U.S. population because of our increased use of CT scans.”
Radiation isn't the only concern, she says: Technology is a major driver behind ballooning health care costs in the United States. “It’s not always true that more tests are better, and it does drive up our health-care costs without a clear benefit to patients," she explains.
If your doctor recommends the CT scan before a stress test, ask for more details, Dr. Redberg says: “How is this going to help my health care; how is it going to help me to feel better?”
Dr. Bonow agrees: “If the doctor is recommending this test, ask the right questions. Does this mean I will never need an invasive angiogram? What is this test going to do?
“What you need is an informed patient asking good questions.”
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