Report from SCCT: Studies emphasize needed changes in cardiac CTA appropriateness criteria

July 11, 2007

Cardiac CT clinical appropriateness criteria published in late 2006 may already need revising, according to researchers who sought to determine the real world efficacy of the guidelines. They presented their studies at the 2007 Society of Cardiovascular Computed Tomography meeting.

Cardiac CT clinical appropriateness criteria published in late 2006 may already need revising, according to researchers who sought to determine the real world efficacy of the guidelines. They presented their studies at the 2007 Society of Cardiovascular Computed Tomography meeting. The American College of Cardiology appropriateness criteria were developed by a panel of experts who voted to consensus on 39 potential indications for cardiac CT angiography. The panel found 13 indications appropriate, 12 uncertain, and 14 inappropriate. Dr. Marcus Y. Chen, a researcher at the Laboratory of Cardiac Energetics with the National Heart, Lung and Blood Institute, presented a study in which he and colleagues at the University of Colorado Health Sciences Center sought to determine if the ACC guidelines led to further diagnostic testing or coronary percutaneous interventions (PCI).Researchers retrospectively evaluated the indications for coronary CTA referrals and adherence to the new appropriateness criteria in 172 consecutive patients. CT studies were performed on a 40-slice scanner.

Tests were scored as Appropriate, Uncertain, Inappropriate, or Not-Classifiable when indications did not fit one of the 39 published indications in the criteria:

  • 72% of referrals fell into the Appropriate category
  • 6%, Uncertain
  • 14%, Inappropriate
  • 8%, Not-Classifiable

A greater portion of the Inappropriate group required subsequent diagnostic testing when compared with the Appropriate group: 25% versus 9% (p = 0.02). More patients within the Uncertain group proceeded to PCI than those in the Appropriate group: 27% versus 3% (p<0.001). A majority of the additional diagnostic testing cases involved catheter angiography as the test of choice versus SPECT imaging.

The two main reasons for appropriate referrals were for:

  • symptomatic detection of coronary disease after uninterpretable or equivocal prior studies
  • patients with acute chest pain who had an intermediate probability of coronary disease but no ECG changes and no positive cardiac enzymes

The three main reasons for inappropriate referrals were for patients:

  • with symptomatic acute chest pain who had a high pretest probability for coronary disease
  • who were asymptomatic and had a low Framingham risk profile
  • who had chest pain but no moderate to severe ischemia on prior stress testing

Regarding uncertain referrals, the main rationales were to:

  • determine if patients were at high risk for noncardiac surgery
  • evaluate patients with chest pain after surgery
  • scan asymptomatic patients who had a high Framingham risk profile

The group of patients in the Not-Classifiable category included mostly those undergoing coronary artery disease evaluations prior to noncoronary artery cardiac surgery or after cardiac transplantation. This group did not have a rate of subsequent diagnostic testing or percutaneous intervention significantly different from those in the Appropriate group.

Researchers suggest that new indications should be considered for the next revision of the appropriateness criteria, perhaps considering assessment of the coronary arteries prior to heart valve surgery. They also suggest strengthening the education of referring physicians and implementing institutional review to ensure quality assurance and adherence to the criteria. An audience member commented that a potential bias of the study is that the data were gathered before the publication of the ACC criteria. Chen agreed, but Dr. Srikanth Sola from The Cleveland Clinic, also in the audience, said that he and colleagues found similar results in a study of 2600 patients. The rate of appropriate indications for patients undergoing CTA scans in 2006 prior to the publication of the criteria was 83%. That number jumped to 90% for the patients scanned in the first three months of 2007 following the criteria's publication. In another study presented at the SCCT meeting, Dr. Casar Bonilla and colleagues at the Cleveland Clinic Florida in Weston sought to assess the clinical indication differences for CTA in the outpatient setting among three guidelines: Regional Medicare (Empire NY/NJ), Local Coverage Determinants (LCD), and the ACC appropriateness criteria. Their retrospective study of 555 consecutive patients found that 13% and 28% had appropriate indications for CTA using the Empire and LCD models, respectively. Using the ACC guidelines, only 1.5% fell within the Appropriate category (

p

≤0.001), while 29% were tagged Uncertain. The other two guidelines do not have an "Uncertain" category.Researchers concluded that indications for cardiac CT can have up to a 10- to 30-fold difference depending on the implementation of each guideline. Moderator Dr. Tracy Callister, director of the Tennessee Heart and Vascular Institute, commented that the majority of coronary CTA studies are ordered for patients with chest pain who have a low to intermediate risk profile. Two of the guidelines allow for that, while the ACC criteria allow for CTA only as a second option after nondiagnostic or equivocal stress tests."The point is made very clear here. If you stick to the ACC guideline, there are actually not many reasons to do cardiac CT," Callister said. He cited a Blue Cross summary study that found the average outpatient sent for diagnostic testing has a pretest probability of 38% ±10%. That means that two out of three patients have less than a 50% chance of having disease. Additionally, data from trials are emerging showing the value of CTA for the low to intermediate risk group to rule out coronary artery disease. "Those of us who like CT would argue that we should do the CT first rather than the nuclear study because CT is more cost-effective and also covers the other causes of chest pain," he said. Dr. Allen Taylor, editor of the new

Journal of Cardiovascular Computed Tomography

, commented that the appropriateness criteria are dynamic and subject to change if they are currently underperforming.