JACC: Coronary CTAs false-positive rate is a concern

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A multicenter, multivendor study found that 64-slice CT angiography can reliably rule out significant coronary artery disease in patients with stable and unstable anginal syndromes, according to a study in the December 2008 Journal of the American College of Cardiology. An accompanying editorial, however, slams the test for its high false-positive rate.

W. Bob Meijboom, MD, and colleagues at three university hospitals in the Netherlands prospectively studied 360 symptomatic patients, ages 50 to 70, who were referred for diagnostic catheter coronary angiography. Each patient also received a coronary CT angiography (CCTA) exam and each center used a 64-slice CT scanner from a different vendor (Sensation 64, Siemens Healthcare; Brilliance 64, Philips Healthcare; and Aquilion 64, Toshiba Medical Systems).

Researchers did not exclude any patients or segments because of impaired image quality attributable to either coronary motion or calcifications. To optimize images, they reconstructed datasets with retrospective electrocardiographic gating using an absolute reverse or percentage technique. They also reconstructed datasets immediately after the scan following a stepwise approach. Because of the retrospective gating, radiation dose was fairly high, between 15 mSv and 18 mSv.

Initially, a single dataset was reconstructed during the mid-to-end diastolic phase (350 ms before the next R-wave or at 65 percent to 70 percent of the R-R interval). In case of insufficient image quality of one or more coronary segments, additional datasets were reconstructed in the diastolic phase (between 250 ms and 450 ms before the next R-wave or between 60 percent and 80 percent of the R-R interval).

In case of persistent artifacts related to coronary motion, an alternative approach using an absolute forward or percentage technique (between 250 and 400 ms after the previous R-wave or between 20 percent and 40 percent of the R-R interval) was used to obtain datasets during the end-systolic phase, according to the study.

Researchers used axial source images, as well as multiplanar or curved reformatted reconstructions and maximum intensity projections, to evaluate the CT dataset for the presence of significant segmental stenosis. They defined significant coronary artery disease (CAD) as >50 percent lumen diameter reduction.

CCTA was found to accurately rule out significant CAD, with a high sensitivity (99 percent) and high negative predictive value (97 percent). Because of overestimation of the severity of a stenosis, the specificity was moderate (64 percent), with a positive predictive value of 86 percent.

The researchers wrote that their stenosis grading policy, and “inclusion of all coronary segments in an intention-to-diagnose approach, is based on the premise that patients with either positive CTA results or nonevaluable segments will undergo catheter angiography. Because the clinical implication is the same, we graded nonevaluable segments as positive, which means that the calculated sensitivity and specificity reflect clinical decision making.”

In his commentary, Steven E. Nissen, MD, from the Cleveland Clinic Foundation, said the study’s data “should give us pause.” He pointed to CCTA’s high false-positive rate in “detecting” obstructions that “simply weren’t there” (in more than 50 percent of the subjects). CCTA also categorized 98 patients with three-vessel disease, but only 19 actually had it, a false-positive rate of 81 percent.

“This high false-positive rate has potentially serious implications, leading to unnecessary and potentially risky procedures that threaten to accelerate already-excessive health care costs,” Nissen wrote. “We must ask ourselves critical questions about the introduction of any costly new technology. Does it improve quality of care compared with existing methods? Does it prolong life or improve quality of life? Does it reduce costs? Is it cost-effective? Are there important safety concerns?”

He continued, “Despite its rapid adoption, for all of these metrics, CT coronary angiography has yet to show that it can deliver on its promise.”

Nissen called for restricted use of CCTA until clinical evidence shows its cost-effectiveness and safety. He called for “real-world” trials that take all comers, including patients with low, medium, and high-risk CAD. Lastly, he said there needs to be outcome studies to show whether CCTA “really improves what we care most about: patient outcomes.”