Seoul, South Korea - In one of the first studies to examine the utility of computed-tomography angiography (CTA) as a screening tool for the detection of coronary artery disease (CAD) in asymptomatic individuals, South Korean researchers conclude that it has the potential to provide good insight [1]. Dr Eue-Keun Choi (Seoul National University Bundang Hospital, South Korea) and colleagues report their findings online July 21, 2008 in the Journal of the American College of Cardiology.

But after weighing up the pros and cons, they say it is far too soon to recommend this as a strategy. "On the basis of our results and considering present radiation-exposure data, we cannot recommend that CTA be used a screening tool for this population at this point." They advocate that further studies be done.

In an accompanying editorial [2], Drs Pim J de Feyter and Carl J Schultz (Thoraxcentre, Erasmus Medical Center, Rotterdam, the Netherlands) concur. "Despite study shortcomings, the authors are to be commended for their efforts to provide initial data concerning the role of CT imaging in asymptomatic subjects. They provided new insights into the prevalence, extent, and severity of coronary atherosclerosis before it has become clinically manifest. [But] we agree with Choi et al that we are far away from recommending CT screening in asymptomatic individuals."

We agree with Choi et al that we are far away from recommending CT screening in asymptomatic individuals.

Both Choi et al and de Feyter and Schultz explain that approximately 50% of all acute coronary syndromes (ACS) occur in previously asymptomatic subjects, so there is a need to identify these people before atherosclerosis becomes clinically manifest and irreversible damage occurs by progression to MI or cardiac death.

The usual way to assess a person's risk is with some kind of model, such as Framingham, but because such asymptomatic subjects are usually at low risk, the prognostic accuracy of such models is far from perfect, they note.

And CTA does have the potential to provide comprehensive information regarding the location, severity, and characteristics of atherosclerotic plaque, say the Korean scientists. But the editorialists say that while they believe there is room for the introduction of a new noninvasive atherosclerotic imaging technique, they wonder what the additional diagnostic value of CTA is compared with, for example, coronary artery calcium screening (CACS).

In their study, Choi and colleagues enrolled 1000 middle-aged subjects (mean age 50 years, 63% men) who themselves sought to undergo 64-slice multidetector row computed tomography as part of a general health evaluation. The researchers say that although eminent institutions, such as the AHA and ACC, have discouraged the use of CTA as a screening process in asymptomatic subjects, "mass-media and market forces have facilitated self-referral within the general public."

They set out to answer two questions: first, to evaluate the prevalence of subclinical coronary atherosclerosis and outline coronary plaque composition in this group of apparently healthy individuals; and second, to pinpoint whether CTA has the potential to identify those at risk more accurately than conventional risk-stratification models.

More than half of the study cohort was considered at low risk, 30% were moderate risk, and 10% high risk; they were followed for an average of 17 months.

Choi et al identified atherosclerotic plaque in 22% of the study population, of whom only 5% had evidence of a significant stenosis and 2% a severe stenosis. The majority had single-vessel disease, and in 77% a stenosis was found on the left main or proximal/mid left anterior descending artery. Forty individuals (4%) had only noncalcified plaques.

These results concur with the few other studies done in this field previously, say de Feyter and Schultz in their editorial.

They "show that . . . the strength of CTA is the fact that this noninvasive technique can identify significant CAD of the left main or three-vessel disease, known to carry worse prognosis, which can be improved by revascularization." But although revascularization might be effective for symptomatic patients or asymptomatic patients at high risk, "this does not necessarily apply to low-risk symptomatic individuals," they point out.

And the next question, they say, is determining the value of CTA to predict adverse coronary events.

In the study by Choi et al, 15 cardiac events occurred in subjects with evidence of CAD, and none occurred in those without CAD. The events consisted of one unstable-angina episode requiring hospital stay and 14 revascularization procedures.

"It is of note that no hard events (death, nonfatal MI) occurred, but more importantly, the revascularization procedures were triggered by the fact that both physicians and patients were unblinded to the CTA outcome data," say de Feyter and Schultz.

"Other outcome data should follow, with physicians and patients blinded to CT outcome, to provide reliable data about the predictive value of CT coronary imaging with respect to hard outcomes," they propose.

They suggest that as well as the blinding issue, the following items should be addressed in future studies of coronary CT imaging:

• Random sample of asymptomatic subjects (non-self-referrals).
• Large sample size, long follow-up (five to 10 years).
• Randomized in case of intervention.
• Calcium screening vs total coronary plaque burden screening.
• Cost analysis (downstream diagnostic tests).
• Hard end point: cardiac death or nonfatal MI.

Finally, both the Korean doctors and the editorialists address the potential issue of harm from CTA due to radiation exposure, with a note that the FDA has announced a small chance of developing a fatal cancer due to a 10-mSv CT study.

Newer CT technology and adapted protocols can significantly reduce the radiation exposure, "but before embracing CT coronary imaging as a routine screening procedure, it needs to be shown that the potential benefits of screening outweigh the harmful effects of CTA," say de Feyter and Schultz.

In conclusion, they say: "The report by Choi et al will hopefully be the first of a large number of studies regarding the establishment of the use of CTA in asymptomatic individuals." But in the meantime, "We abide by the recommendation statement of the US Preventive Services Task Force against routine screening with resting electrocardiography, exercise treadmill test, and electron-beam CT in adults at low risk, which should also apply to CTA screening."