title: Transluminal attenuation gradient in coronary computed tomography angiography is a novel noninvasive approach to the identification of functionally significant coronary artery stenosis: a comparison with fractional flow reserve.
abstract: OBJECTIVE
  The purpose of this study was to assess the diagnostic accuracy of TAG320 in predicting functional stenosis severity evaluated by fractional flow reserve (FFR).
  
  
  BACKGROUND
  Coronary computed tomography angiography (CCTA) has limited specificity for predicting functionally significant stenoses. Recent studies suggest that contrast gradient attenuation along an arterial lesion, or transluminal attenuation gradient (TAG), may provide assessment of functional significance of coronary stenosis. The use of 320-detector row computed tomography (CT), enabling near isophasic, single-beat imaging of the entire coronary tree, may be ideal for TAG functional assessment of a coronary arterial stenosis.
  
  
  METHODS
  We assessed the diagnostic accuracy of TAG320 using 320-row CCTA with FFR for the evaluation of functional stenosis severity in consecutive patients undergoing invasive coronary angiography and FFR for stable chest pain. The luminal radiological contrast attenuation (Hounsfield units [HU]) was measured at 5-mm intervals along the artery from ostium to a distal level where the cross-sectional area decreased to <2.0 mm(2). TAG320 was defined as the linear regression coefficient between luminal attenuation and axial distance. Functionally significant coronary stenosis was defined as ≤0.8 on FFR.
  
  
  RESULTS
  In our cohort of 54 patients (age 62.7 ± 8.7 years, 35 men, 78 vessels), TAG320 in FFR-significant vessels was significantly lower when compared with FFR nonsignificant vessels (-21 [-27; -16] vs. -11 [-16; -3] HU/10 mm, p < 0.001). On receiver-operating characteristic analysis, a retrospectively determined TAG320 cutoff of -15.1 HU/10 mm predicted FFR ≤0.8 with (a bootstrapped resampled) a sensitivity of 77%, specificity of 74%, positive predictive value of 67%, and negative predictive value of 86%. The combined TAG320 and CCTA assessment had an area under the curve of 0.88. There was incremental value of adding TAG320 to CCTA assessment for detection of significant FFR by Wald test (p = 0.0001) and integrated discrimination improvement index (0.11, p = 0.002).
  
  
  CONCLUSIONS
  Assessment of TAG320 with a 320-detector row CT provides acceptable prediction of invasive FFR and may provide a noninvasive modality for detecting functionally significant coronary stenoses. Combined TAG320 and CCTA assessment may have incremental predictive value over CCTA alone for detecting functionally significant coronary arterial stenoses; however, larger studies are required to determine the benefit of combined TAG320 and CCTA assessment.
authors: Monash Cardiovascular Research Centre, Department of Medicine (Monash Medical Centre), Monash University and Monash Heart, Southern Health, Clayton, Australia.
authors: Dennis T L
authors: DT
authors: Wong
authors: Brian S
authors: BS
authors: Ko
authors: James D
authors: JD
authors: Cameron
authors: Nitesh
authors: N
authors: Nerlekar
authors: Michael C H
authors: MC
authors: Leung
authors: Yuvaraj
authors: Y
authors: Malaiapan
authors: Marcus
authors: M
authors: Crossett
authors: Darryl P
authors: DP
authors: Leong
authors: Stephen G
authors: SG
authors: Worthley
authors: John
authors: J
authors: Troupis
authors: Ian T
authors: IT
authors: Meredith
authors: Sujith K
authors: SK
authors: Seneviratne
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D015331:Cohort Studies; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging / Q000503:physiopathology; D023921:Coronary Stenosis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D005260:Female; D053805:Fractional Flow Reserve, Myocardial / Q000502:physiology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography / Q000379:methods*; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity