More evidence is needed to support the value of non-invasive imaging techniques such as computer tomographic angiography (CTA) in making a diagnosis or prognosis for coronary artery disease, CMS' Medicare Coverage Advisory Committee concluded during a May 18 meeting.

On a scale of one to five between "very confident" and "very unconfident" the panel, on average, voted right down the middle, indicating they were "unsure" if sufficient evidence exists that CTA is an effective adjunct to or replacement for the more invasive gold standard, coronary artery catheterization.

Physicians representing several groups including the American College of Radiology and the American College of Cardiology tried to convince the panel that technologies such as CTA can both detect and rule out the presence of coronary artery disease in patients with low to moderate pre-test likelihood of disease.

The presenters suggested that the screening tool could be used like a gatekeeper to help physicians more effectively triage patients that need to go to the catheterization lab for more invasive procedures for diagnosis and treatments.

Only patients with a high likelihood of requiring intervention for truly ischemia-producing lesions should have diagnostic catheterization, Kim Williams, MD, said, speaking on behalf of the American College of Cardiology.

Proponents noted that the negative predictive value of the test is its most attractive benefit. Moreover, CTA would save low-risk patients the risk and inconvenience of an invasive procedure, which carries serious and potentially life-threatening complications, including arrhythmias, stroke and myocardial infarction.

However, panelists were eager to see more data on clinical outcomes. "There remains a yawning gap" between this evidence and that typically required by practice guidelines or payors, said David Cohen, MD, MSc, Beth Israel Deaconess Medical Center.

The panel members relied on a draft technology assessment commissioned by the Agency for Healthcare Research & Quality that said available data are lacking on CTA, magnetic resonance angiography (MRA) and other non-invasive approaches.

The analysis, conducted by the Duke Center for Clinical Health Policy Research Evidence-Based Practice Center, was based on 29 CTA studies and 13 studies evaluating MRA.

Larger, Less Selected Populations Required

"There is limited evidence regarding test performance of [non-invasive imaging tests] for identifying, quantifying or otherwise characterizing coronary artery stenoses," the report concludes.

The available studies, which were generally small and performed at single centers, "primarily fall into the 'proof of concept' category," it says. "Future work will need to examine these tests in larger, less selected populations representing the clinical settings in which they are actually expected to be used."

Much of the data reviewed by MCAC and BlueCross BlueShield were from 16-slice multi-detector computed tomography. Only six published studies compare CT using 64-slice technology to conventional angiography.

Some physicians presenting at the meeting pointed out that the16-slice technology is being replaced in clinical practice with much higher resolution 64-slice scanners.

Elliot Fishman, MD, Johns Hopkins University, who represented the American College of Radiology, said of the 16-slice technology: "if you have the perfect patient and the sun and the moon and the stars line up, you can get a good study." On the other hand, 95% of images taking in all patient populations come out clear with 64-slice equipment, he said.

Lynne Hurwitz, MD, Duke University, who presented the tech assessment, acknowledged the improvements in the 64-slice technology, however, she noted that it is not uncommon to have blurred images due to respiratory or coronary motion.

Almost all studies have shown that coronary CTA has exposed patients to notably more radiation than traditional angiography.

Panel members were more supportive of the 64-slice technology than the older versions. Several members expressed confidence in the test's effectiveness in pre-operative procedures such as aortic valve replacement.

However, some panelists were not persuaded by any of the data. Rita Redberg, MD, MSc, University of California, San Francisco Medical Center, countered stakeholder claims that CTA would reduce cardiac catheterization. She hypothesized that false positives would actually increase referrals for additional investigational procedures.

Panelists also wanted to clearly define the population for which the technology would be used. They also were concerned about the potential for physicians to increase screenings in order to pay for the device. However, Williams noted that the ACC is developing guidelines on appropriate use of the technology.

Panel chair Alan Garber, MD, PhD, Stanford University, queried whether the agency was premature in assessing the evidence base of the emerging technology.

In 2000, the American Heart Association estimated that more than 12 million people had ischemic heart disease. The economic cost approached $120 bil. that year. It is the most common, serious life threatening illness in the U.S.

Siemens Medical Solutions, GE Healthcare, Philips Medical and Toshiba Medical all manufacture 64-slice CT scanners.

The Medicare Coverage Advisory Committee provides advice and recommendations about whether scientific evidence for certain medical technologies and services warrants consideration of expanded Medicare coverage.

The panel's conclusion follows a negative assessment of CTA by the BlueCross BlueShield Technology Evaluation Center in 2005 (¹ Also see "Coronary Artery Diagnostic Tool Fails To Win Blues TEC Endorsement" - Medtech Insight, 20 June, 2005., p. 23).

- Katherine Thomas

Medicare Panel Calls For Outcomes Data On Non-Invasive Coronary Imaging

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