Radiology: 64-slice CT shows some accuracy in grading coronary artery stenoses

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Newer technology for 64-slice CT could be an effective diagnostic tool for ruling out coronary artery disease (CAD) or for making a positive diagnosis in high-risk patients; however, findings must be interpreted with caution, according to a study in this month's issue of Radiology.

Hervé Gouya, MD, from the department of radiology at the University Paris Descartes and Hôpital Cochin in Paris, and colleagues sought to assess the diagnostic accuracy of multidetector (64-slice) CT versus coronary angiography in detection of and assignment of grades for coronary artery stenoses in a high-risk population and to investigate causes for discordance between the two.

The study included 114 high-risk patients (103 men, 11 women; mean age, 63 years) with potential myocardial ischemia. Two radiologists with unequal experience in reading coronary CT angiograms independently interpreted CT images. They assessed the diagnostic performance of CT in detection of stenoses of 50 percent or more per patient, per artery and per segment.

Gouya and colleagues reported that 68 percent of patients had stenoses of 50 percent or more. The readers found good interrater agreement, with ? values of 0.77-0.85. For the most experienced radiologist, the sensitivity, specificity, positive likelihood ratio and negative likelihood ratio were 73.4 percent, 95 percent, 14.7, and 0.28 per segment, 95.2 percent, 94.7 percent, 18 and 0.05 per artery, and 100 percent, 89.2 percent, 9.26 and zero per patient, respectively.

The authors said that the discordance between 64-slice CT and coronary angiography was related to either under- or overestimation of the degree of stenosis, anatomic misclassification and coronary artery segments that were not assessable at 64-slice CT. Bland-Altman analysis showed poor agreement, especially for intermediate stenosis (mean bias, 1.3 percent; 95 percents limits of agreement: -27.3 percent, 29.9 percent).

Despite excellent sensitivity and negative likelihood ratios in a per-patient or per-vessel analysis, some coronary artery stenosis remained misdiagnosed with 64-slice CT, resulting in limited sensitivity on a per-segment basis owing to anatomic discordance and failure to accurately quantify intermediate stenosis, the authors concluded. "Although assigning a stenosis to the wrong vessel (eg, first instead of second marginal obtuse branch) is clinically nonrelevant, underestimation of the degree of stenosis can lead to inappropriate therapy," they wrote.

Although the results show the high diagnostic accuracy of 64-slice CT compared with coronary angiography on a per-patient and a per-artery basis, some stenoses remain misdiagnosed, and this misdiagnosis results in a limited sensitivity at the per-segment level, Gouya and colleagues noted.

"Discrepancies between coronary angiography and 64-slice CT are mostly caused by assignment of a stenosis to the wrong coronary artery segment and poor agreement for quantification of coronary artery stenosis diameter, especially for evaluation of intermediate stenosis," the authors cautioned, and the "results should be applied cautiously in a population with a different pretest risk for CAD."