Obstructive Coronary Artery Disease: Reverse Attenuation Gradient Sign at CT Indicates Distal Retrograde Flow-A Useful Sign for Differentiating Chronic Total Occlusion from Subtotal Occlusion

Purpose: To study the clinical importance of the reverse attenuation gradient (RAG) sign in patients with occlusive coronary artery disease observed with coronary computed tomographic (CT) angiography. Materials and Methods: All patients provided written informed consent, and the institutional review board committee approved the study protocol. Eighty consecutive patients (mean age, 67.1 years +/- 12.1 [standard deviation]; range, 35-87 years; 62 men [mean age, 65.8 +/- years +/- 12.5; range, 35-86 years] and 18 women [mean age, 71.7 years +/- 9.3; range, 58-87 years]) were enrolled prospectively in this study. The RAG sign was defined as the reverse intraluminal opacification gradient of vessels distal to the occlusive lesions, which has lower attenuation in the proximal segment and gradually increased attenuation along the vessel. Other parameters, such as lesion length and bridging collateral vessels visible at coronary CT angiography, were recorded. Mann-Whitney Wilcoxon and Fisher exact tests were used for comparison. Results: There were 94 occlusive lesions. Invasive coronary angiography was used to confirm 49 chronic total occlusions (CTOs) and 45 subtotal occlusions (SOs). The CTO group had the RAG sign significantly more frequently than did the SO group (65% [32 of 49] vs 7% [three of 45]; P < .001). Similarly, significant difference of measurements of the attenuation gradient (5.1 HU/10 mm +/- 13.4 vs -13.4 HU/10 mm +/- 8.7; P < .001) and lesion length (23.6 mm +/- 22.7 vs 6 mm 6 3; P,.001) was noted between the groups. Bridging collateral vessels were present in only four cases of CTO at coronary CT angiography. All segments with RAG at coronary CT angiography were shown by means of invasive coronary angiography to be supplied by retrograde collateral vessels. When a combination of all those parameters was used for diagnosis of CTO, sensitivity and specificity were 90% (44 of 49) and 93% (42 of 45), respectively. Conclusion: The RAG sign represents the retrograde collateral flow distal to an occlusive lesion. This sign is highly specific for CTO and helps to differentiate CTO from SO. (C) RSNA, 2012