Detecting Heart Disease Noninvasively Post 1

At some point, nearly everyone wonders how his or her coronary arteries are doing. People with coronary artery disease would like to know if drugs, procedures, and lifestyle changes are helping to clear their arteries, and people with cardiovascular risk factors worry about having a heart attack or needing bypass surgery. Even people at low risk may be concerned about their heart’s health.

That’s why a newly popular — and controversial— method of scanning the coronary arteries is getting a lot of attention: electron beam computed tomography, or EBCT, a form of the familiar CAT scan (see picture). In EBCT, an x-ray scanner detects calcium buildup in the arteries, generating a number called the calcium score. Many studies have found that the calcium score correlates with the amount of artery-obstructing plaque. A new variation of EBCT called contrast EBCT can even make images that pinpoint the location of blockages, though this type of scanning isn’t yet widely available.

The appeal of EBCT is clear. It’s noninvasive, unlike angiograms, which require the cardiologist to guide a catheter into the heart from a distant blood vessel in the arm or leg. It’s fast, taking only about 15 minutes, compared to the hours needed for the most commonly used noninvasive screening method, the thallium stress test. And it’s relatively inexpensive — although it’s not generally covered by insurance, an EBCT scan can be performed for about $475. This has led to some EBCT clinics to advertise scans on the radio, in newspapers, and even on billboards. Predictably, the aggressive advertising has led to controversy. Although EBCT may be noninvasive, fast, and inexpensive, cardiologists aren’t so sure that it’s useful or worth paying for out-of-pocket.

A study in the December 31, 1998, New England Journal of Medicine sought to find out how useful and accurate EBCT could be. Researchers asked 125 people scheduled for an angiogram to undergo an EBCT scan, the still-experimental contrast form. With the angiogram representing the “true state” of each person’s coronary arteries, the reliability of the EBCT scan was judged by how well it matched the angiogram.

Overall, the EBCT scans were quite accurate when held up to this standard — about as reliable as the average treadmill stress test in identifying people with blocked arteries. EBCT accurately detected blockages 92 percent of the time and correctly ruled out blockages 94 percent of the time. The drawback appeared to be the difficulty of getting usable images with the contrast form of EBCT; only about two thirds of participants could be screened because the researchers couldn’t get good images in the others.

Unlike this fancier contrast form of EBCT, the regular, noncontrast form can’t make images. But its relatively simple action — measuring calcium buildup — has shown some promise. Another study in the same issue of the NEJM found that calcium measurements taken with noncontrast EBCT effectively track the amount of plaque in someone’s arteries. And in a new use for noncontrast EBCT, described in a November 1, 1998, report in the Journal of the American College of Cardiology, doctors can use the scans to identify the kind of cardiomyopathy a person has.

Cardiomyopathy, a broad term for weakness and disease of the heart muscle, stems from a range of causes — from viruses to genetics to coronary artery. Knowing the cause of a person’s cardiomyopathy is crucial to picking the right therapy, such as bypass surgery for clogged arteries, but it’s been hard to find a reliable, noninvasive method for making the assessment. The study found that EBCT scans were about 92 percent accurate in determining whether cardiomyopathy was caused by clogged arteries.

Comments are closed.