Evidence demonstrates CT accuracy for CABG obstruction evaluation

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A meta-analysis of diagnostic performance of 16- and 64-slice CT for coronary artery bypass graft assessment (CABG) showed evidence that the modality provided high accuracy for the evaluation of CABG obstruction in assessable conduits, according to research published this month in the journal Radiology.

“Promising results for bypass patency evaluation were reported with the first-generation (4- and 8-slice) multisection CT scanners, but there was a major limitation related to the presence of a large number of unassessable grafts because of motion artifact, presence of surgical wires or clips, and heavy calcification,” the scientists wrote. “The introduction of 16- and, more recently, 64-section scanners promises to reduce the number of unassessable grafts, improving the diagnostic accuracy of multisection CT for helping detect graft disease.”

A group from the departments of radiology, thoracic and cardiovascular surgery, nuclear medicine, cardiology and statistics from the University Hospital of Caen in Normandy, France, along with colleagues from the Institut Pasteur in Lille and S. Anna Hospital in Ferrara, Italy, constructed a meta-analysis of peer-reviewed published literature in multiple languages through 2007 to evaluate the accuracy of 16- and 64-slice CT for assessment of CABGs.

“Only studies evaluating the presence of significant obstructive coronary artery bypass disease (50 percent lumen reduction) as a result of coronary angiography and multisection CT in the same patients were included,” they noted.

The study authors also restricted their analysis to studies that reported cases in absolute numbers of true-positive, false-positive, true-negative, and false-negative results. In addition, the studies had to have used coronary angiography as the reference standard for diagnosing obstructive CABG disease.

From an initial field of 158 potential relevant citations, the researchers applied their criteria and refined their meta-analysis to 15 studies published between June 2004 and May 2007. Their data cohort included 723 bypass-graft patients with a mean age of 65.

Pooled data on 2,023 grafts assessed with CT for the existence of occlusion or substantial stenoses demonstrated a sensitivity of 97.6 percent, and specificity of 96.7 percent, a positive predictive value to 92.7 percent, and  a negative predictive value of 98.5 percent for diagnostic performance. Occlusion analysis of 1,308 grafts showed a sensitivity of 99.3 percent and a specificity of 98.7 percent; while stenosis analysis of 871 non-occluded grafts delivered a sensitivity of 94.4 percent and a specificity of 98 percent.

“The results of our meta-analysis demonstrate that obstructive bypass graft disease can be detected by using at least a 16-section CT with a high diagnostic accuracy with a sensitivity of 98 percent, a specificity of 97 percent, a positive predictive value of 93 percent and a negative predictive value of 99 percent, albeit with only 92.4 percent of scanned grafts being fully assessable,” the authors wrote.

They observed that CT angiography (CTA) is a less invasive technique than traditional coronary angiography, which takes more time, uses more contrast agent, and has an increased complication rate. They also noted that coronary angiography sometimes has difficulty in locating the origin of grafts and exploring them selectively. Also, for patients who need repeat cardiac bypass surgery, CTA provides surgeons with precise information about existing graft position as well as the existence of calcification of the aorta.

“Multisection CT provided high accuracy for the evaluation of CABG obstruction in assessable conduits, and might be used as a noninvasive tool for the evaluation of suspected graft dysfunction in patients who are at high risk for complications from coronary angiography,” the authors stated.