EBCT debate heats up in wake of new ACC, AHA guidelines

A conservative consensus statement on the use of electron- beam CT to image coronary calcium does not appear to be quelling interest in the technology. The device’s sole manufacturer expects sales to double this year, even as debate around the technique intensified this summer.

The statement, jointly issued by the American College of Cardiology and the American Heart Association in July, conceded that coronary calcium indicates the presence of plaque, and that a low EBCT score presages a low likelihood of adverse cardiovascular events in two to five years. A high score, on the other hand, indicates a moderate to high risk for the same period.

Citing a shortage of conclusive studies on whether the test is better than or adds to data provided by other tests or risk assessments, the consensus panel limited its recommendations for EBCT to the following patients:

• asymptomatic elderly patients whose treatment may change based on calcium findings;

• patients whose previous tests or other risk factors indicate possible, but not conclusive, evidence of high risk for heart disease; and

• asymptomatic patients who are having a complete cardiac workup and whose results from the traditional tests were inconclusive.

Measuring the increase or decline of calcium over time was called a “promising application” of the technology but one not studied sufficiently to be included in the guidelines.

“The consensus paper was a backlash, not against the technology or its predictive ability, but against the direct advertising to the public,” said Dr. Matthew Budoff, an assistant professor of medicine at the University of California, Los Angeles, and a leading EBCT researcher. Even so, “the document suggests testing for patients at intermittent risk or the elderly—and that’s 30% to 40% of Americans,” he said.

Imatron, the manufacturer, predicts that the guidelines will not dampen interest in the technology. CEO S. Lewis Meyer expects to sell at least 30 units this year, up from 18 in 1999.

“How else can you treat patients if you don’t find disease early?” Budoff said. “You can tell patients that they’re at high risk, and talk about cholesterol scores, but when you show them white specks of calcium on their CT, they get religion.”

The body of research on EBCT is gradually sorting out its potential: whether it can predict disease, how it compares to other risk predictors, and whether spiral CT can offer comparable accuracy.

Among the findings of other studies are the following:

• EBCT can track the degree at which plaque increases, decreases, or stabilizes over time, according to Vanderbilt University researchers in the New England Journal of Medicine, Dec. 31, 1998;

• ECG-triggered, single-slice conventional CT comes the closest to EBCT in quantifying calcium scores, according to German researchers in the February 2000 issue of the American Journal of Roentgenology;

• Calcium screening is cost-effective in groups with low or moderate risk of heart disease, while angiography is more cost-effective in patients at high risk, according to Mayo Clinic researchers reporting in the Journal of the American College of Cardiology, February 1999; and

• Neither risk-factor assessment nor EBCT calcium screening can accurately predict coronary events in asymptomatic high-risk adults, according to UCLA researchers writing in the Feb. 15, 2000, issue of Circulation.

Manufacturers of mechanical CT are jumping on the bandwagon, pushing for faster scan times and other modifications to move their technology closer to EBCT. Imatron’s Meyer believes buyers will heed the body of more than 500 studies and gravitate toward his machines. But Dr. John Rumberger, who developed guidelines on EBCT use at the Mayo Clinic and has published a number of EBCT studies, agrees.

“Merely sharing a moniker of ‘x-ray computed tomography’ with EBT (Imatron’s designation for the technology) does not imply validity (for mechanical scanners),” Rumberger wrote in an open letter to spiral CT users and manufacturers. His letter blasted claims that EBCT is equivalent to spiral CT calcium screening.

“There are no current peer-reviewed published papers that support these claims,” he wrote.

The data might be available soon, however: A major National Institutes of Health study launched in July will compare the four-year progress of 6500 patients scanned with one or the other type of calcium screening.

“There are still problems with single-detector CT that need resolution, not the least of which is the necessity of two or more breath-holds to encompass the entire coronary tree,” said Dr. William Stanford, a professor of radiology at the University of Iowa, at the Second Annual International Symposium on Multidetector-Row CT in June.

“Besides, all three technologies (EBCT, single-detector CT, and multiple-detector CT) are still undergoing innovation and improvement. Most would agree, though, that at present the detail of the electron-beam images is generally better and there is less motion artifact than with helical CT,” he said. “HCT is here to stay. It is imperative that we band together to validate the methodology.”