Los Angeles, CA - A largely abandoned imaging test is providing some welcome new insights about the technology it produced: researchers in California using CT angiograms taken with electron-beam tomography (EBT) scanners have shown than the images can predict mortality among patients with suspected coronary artery disease (CAD) [1]. They say the findings represent the first solid outcome data supporting a role for CT angiography in predicting all-cause mortality.

"All the other studies that have been published have almost entirely been on coronary calcium scanning and outcomes, but this study was looking at whether CT angiography (CTA) predicts outcomes, and there are virtually no data in the literature looking at this," senior author Dr Matthew Budoff (Harbor-University of California, Los Angeles [UCLA] Medical Center, Torrance) told heartwire. "We now have some evidence that the plaque we see on CT angiography and the stenosis we see on CTA actually have prognostic implications."

The study appears in the October 14, 2008 issue of the Journal of the American College of Cardiology.

Today, most of the excitement—and controversy—over CT angiography has centered on multislice scanners with 64 detectors or more. But as Budoff, with first author Dr Matthew Ostrom and colleagues (UCLA), point out in their paper, much-needed outcome data, linking angiographic burden identified by CTA to subsequent adverse events, are hard to come by, since the technology itself is so new and patient follow-up is limited.

For their study, Ostrom et al reviewed CT angiograms for 2538 patients who underwent CTA using EBT during the late 1990s and early 2000s. All patients had no known CAD at the time of their scans; their CAD was categorized by EBT scan as obstructive or nonobstructive CAD in one, two, or three vessels.

After a mean follow-up of more than six years (and a maximum of 12 years) patients diagnosed with CAD by CT angiography were significantly more likely to have died than patients with no evidence of CAD by CT angiography at baseline, a finding that remained significant after adjustment for CAD risk factors. Ostrom et al further demonstrated a clear trend wherein patients with nonobstuctive CAD in one vessel were more likely to survive than patients with two- or three-vessel nonobstructive disease, increasing all the way across the spectrum to patients with three-vessel obstructive CAD, in whom survival was the lowest. Moreover, coronary artery calcium score, added to presence or absence of CAD by EBT angiography, increased the predictive power of the test.

"The primary results of our study reveal that the burden of angiographic disease detected by CTA positively correlates with the incidence of all-cause mortality among patients with suspected CAD referred for evaluation in an outpatient setting," Ostrom et al write. "This is the first study to demonstrate that CTA is incremental to traditional risk factors plus coronary calcium in predicting all-cause mortality. . . . To our knowledge, this cohort represents the largest and longest follow-up after CTA in such a population and is one of few studies demonstrating the prognostic value of this technology."

To heartwire, Budoff emphasized that the newer, 64-slice scanners would undoubtedly be better for visualizing plaques and defining stenosis, but it will be some time before outcome data are available for 64-slice CTA. "I am confident 64-slice will do better, but we won't have 10-year data for another seven years," he predicted.

And still to be established, he notes, is how the prognostic capacity of CTA compares with that of other imaging modalities, such as conventional invasive angiography and nuclear imaging for hard outcomes. Other outstanding questions include which patients are best suited to noninvasive CTA, as opposed to other screening modalities, and how much radiation dose can be minimized.

"Radiation exposure [from CTA] at our site has been diminishing over the years—we've been averaging under 10 mSv for CTA over the past three years, and we continue to find ways of reducing radiation exposure with prospective imaging and by reducing the scan parameters to lower radiation exposure to our patients," Budoff said.

Conventional invasive angiography, he added, is between 2 to 5 mSv, while nuclear imaging is higher, ranging from 8 to 20 mSv.

Newer CT scanners, with 128 detectors or higher, will be a mixed blessing, Budoff notes—something that may provide reassurances to centers that have already invested in 64-slice scanners. "I think the radiation dose will go up with the next-generation scanners, because when you have more detectors, the radiation dose goes up. The diagnostic accuracy may go up a little bit, and the number of noninterpretable studies may go down a little bit, but you will be paying a price both because the cost of the machines will go up and in terms of higher radiation exposure."