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Noninvasive computed tomography angiography (CTA) can be a cheaper alternative to invasive cardiac catheterization in diagnosing coronary artery disease, researchers performing a decision-tree analysis said.

Using coronary CTA to screen for coronary artery disease reduced the diagnostic cost per patient by an average of $759 for patients who test positive on a stress test, but who otherwise have no symptoms and are at a less than 50% chance of significant coronary artery disease, according to an online report in the American Journal of Roentgenology.

Patients who were diagnosed using CTA had a false-negative diagnosis rate of 2.5%, which is comparable to the false-negative rate of stress testing, and they received an additional 1-2 mSv of radiation exposure, reported Ethan J. Halpern, MD, of Thomas Jefferson University in Philadelphia, and colleagues.

"For a patient at low risk who has no symptoms and has a positive stress test result, our results suggest that preliminary coronary CTA rather than direct triage to cardiac catheterization is a cost-effective alternative," they wrote.

Although routine screening for coronary artery disease (CAD) in patients with no symptoms is not endorsed by practice guidelines, asymptomatic patients with cardiac risk factors often undergo exercise stress testing, especially before surgery or starting an exercise program. Many patients with low to intermediate risk for indications such as atypical chest pain and multiple cardiac risk factors also undergo stress tests.

Patients who test positive for CAD on stress tests but show no other symptoms of the disease are often referred for diagnostic catheter angiography. Very few of these patients have CAD, according to unpublished findings by Halpern and colleagues.

"To reduce the number of catheterization procedures performed in which the coronary arterial anatomy is found to be normal," they wrote, "it may be beneficial to offer coronary CT angiography to these patients as a noninvasive alternative to immediate cardiac catheterization."

The researchers constructed a decision tree to compare the false-negative rates, false-positive rates, costs, and radiation exposure of direct referral of patients for cardiac catheterization with those of coronary CTA before catheterization. They assumed that patients referred for coronary CTA proceed to catheterization only when they are diagnosed with stenosis causing greater than 50% reduction in vessel diameter.

They determined the costs for coronary CTA and diagnostic catheterization based on the 2009 Medicare fee schedule for physician services and obtained data on the tests' sensitivity, specificity, and radiation dose through a literature review. The average cost to Medicare was $508 for coronary CTA and $2,948 for cardiac catheterization.

The cost reduction associated with coronary CTA alone depended on the prevalence of coronary artery disease. Overall costs of performing coronary CTA before triage to cardiac catheterization were reduced as long as the prevalence was less than 85%. CTA reduced average diagnostic costs by $789 with a CAD prevalence of less than 50% and by $1,000 at a CAD prevalence of less than 75%.

The authors noted that all decision-tree analyses are limited by the underlying assumptions made. In this study, analysis was limited to Medicare data and that medical charges and reimbursements vary widely across locations and insurance plans. Radiation dose also varies depending on the brand of CT machine used. They also cautioned that, although their study focused on patients without symptoms of CAD, they used sensitivity and specificity values for coronary CTA that were obtained from studies of patients with symptoms of CAD.