NEJM: Coronary CTA inches closer to Dx cath, but falls short
Heart scan with the Toshiba Aquilion 64-slice scanner. Image Source: Advanced Imaging Newport Coast  
Multidetector CT angiography accurately identifies the presence and severity of obstructive coronary artery disease and subsequent revascularization in symptomatic patients. The negative and positive predictive values, however, indicate that CTA cannot replace conventional coronary angiography at present, according to a study published Nov. 27 online in the New England Journal of Medicine.

In an accompanying editorial, two cardiologists slam the Centers for Medicare & Medicaid Services (CMS) for reimbursing coronary CTA (CCTA) scans without sufficient evidence.

Investigators at nine medical centers involved in the CorE-64 study analyzed 64-row multidetector CCTA data from 291 symptomatic men and women with calcium scores less than 600, who were already scheduled to have diagnostic cath.

A total of 56 percent of patients had obstructive coronary artery disease (CAD). The patient-based diagnostic accuracy of quantitative CCTA for detecting or ruling out stenoses of 50 percent or more according to conventional angiography revealed:
  • an area under the curve (AUC) of 0.93
  • sensitivity of 85 percent
  • specificity of 90 percent
  • positive predictive value of 91 percent, and
  • negative predictive value of 83 percent.
Researchers reported that the AUC is “consistent with robust diagnostic performance and indicates that 64-row multidetector CT angiography has powerful discriminative ability to identify, among symptomatic patients, those with and those without coronary obstruction.”

But because of the low positive and negative predictive values, they concluded that CCTA is not ready to replace conventional angiography in this patient population, those with a higher risk of disease.

CCTA and conventional angiography were similar in their ability to identify patients who subsequently underwent revascularization: the AUC was 0.84 and 0.86 for CCTA and conventional angiography, respectively.

Researchers led by Julie Miller, MD, from Johns Hopkins University School of Medicine, cautioned that the diagnostic performance of CCTA should be considered in the context of commonly used noninvasive stress tests, coupled with imaging techniques or not. They pointed out that CCTA misclassified 13 percent of patients compared with conventional angiography.

CCTA is not a substitute for catheterization, but “an alternative diagnostic tool to rule in or rule out stenoses” when other tests such as SPECT imaging are "unclear or unsafe for a particular patient,” said senior author João Lima, MD, a cardiologist at Hopkins.

In an accompanying editorial titled “Pay Now, Benefits May Follow—The Case of Cardiac Computed Tomographic Angiography,” Rita F. Redberg, MD, and Judith Walsh, MD, suggested that the CMS didn’t do its homework when it chose to allow local carriers to continue to reimburse for coronary CTA.

“The use of cardiac imaging has been increasing by 26 percent per year, despite a lack of evidence of outcome benefit,” the authors wrote. They also suggested that the “fee-for-service system encourages the use of expensive but unproven medical devices by generously reimbursing for new procedures without regard to their benefit.”

Udo Hoffmann, MD, director of CT research at Massachusetts General Hospital, disagrees with the editorial comments. He told Cardiovascular Business News that CMS made the decision to continue to reimburse for coronary CTA based on the expanded evidence it received. “CT is going to be a very useful tool, but it takes time and resources to collect a body of literature, from which to make right diagnostic and treatment decisions,” he said.

He echoed the conclusions of Miller et al, saying that CCTA is a triage tool for coronary angiography, not a substitution for it.

Redberg, who reports receiving grant support from the Blue Shield of California Foundation, is director of women's cardiovascular services at the University of California, San Francisco Medical Center. Walsh is a professor of clinical medicine and epidemiology at the UCSF School of Medicine.  

Toshiba provided funding support for the CorE-64 study, which used its Aquilion 64-multidetector CT scanner.