title: Additional value of transluminal attenuation gradient in CT angiography to predict hemodynamic significance of coronary artery stenosis.
abstract: OBJECTIVE
  The current study evaluates the incremental value of transluminal attenuation gradient (TAG), TAG with corrected contrast opacification (CCO), and TAG with exclusion of calcified coronary segments (ExC) over coronary computed tomography angiogram (CTA) alone using fractional flow reserve (FFR) as the gold standard.
  
  
  BACKGROUND
  TAG is defined as the contrast opacification gradient along the length of a coronary artery on a coronary CTA. Preliminary data suggest that TAG provides additional functional information. Interpretation of TAG is hampered by multiple heartbeat acquisition algorithms and coronary calcifications. Two correction models have been proposed based on either dephasing of contrast delivery by relating coronary density to corresponding descending aortic opacification (TAG-CCO) or excluding calcified coronary segments (TAG-ExC).
  
  
  METHODS
  Eighty-five patients with intermediate probability of coronary artery disease were prospectively included. All patients underwent step-and-shoot 256-slice coronary CTA. TAG, TAG-CCO, and TAG-ExC analyses were performed followed by invasive coronary angiography in conjunction with FFR measurements of all major coronary branches.
  
  
  RESULTS
  Thirty-four patients (40%) were diagnosed with hemodynamically-significant coronary artery disease (i.e., FFR ≤0.80). On a per-vessel basis (n = 253), 59 lesions (23%) were graded as hemodynamically significant, and the diagnostic accuracy of coronary CTA (diameter stenosis ≥50%) was 95%, 75%, 98%, and 54% for sensitivity, specificity, negative predictive value, and positive predictive value, respectively. TAG and TAG-ExC did not discriminate between vessels with or without hemodynamically significant lesions (-13.5 ± 17.1 HU [Hounsfield units] × 10 mm(-1) vs. -11.6 ± 13.3 HU × 10 mm(-1), p = 0.36; and 13.1 ± 15.9 HU × 10 mm(-1) vs. -11.4 ± 11.7 HU × 10 mm(-1), p = 0.77, respectively). TAG-CCO was lower in vessels with a hemodynamically-significant lesion (-0.050 ± 0.051 10 mm(-1) vs. -0.036 ± 0.034 10 mm(-1), p = 0.03) and TAG-ExC resulted in a slight improvement of the net reclassification index (0.021, p < 0.05).
  
  
  CONCLUSIONS
  TAG did not provide incremental diagnostic value over 256-slice coronary CTA alone in assessing the hemodynamic consequences of a coronary stenosis. Correction for temporal nonuniformity of contrast delivery or exclusion of calcified coronary segments slightly enhanced the results.
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Wynand J
authors.initials: WJ
authors.lastname: Stuijfzand
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Danad
authors.affiliation: Department of Radiology, Nuclear Medicine, and PET Research, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Pieter G
authors.initials: PG
authors.lastname: Raijmakers
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: C Bogdan
authors.initials: CB
authors.lastname: Marcu
authors.affiliation: Department of Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Martijn W
authors.initials: MW
authors.lastname: Heymans
authors.affiliation: Department of Radiology, Nuclear Medicine, and PET Research, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Cornelis C
authors.initials: CC
authors.lastname: van Kuijk
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Albert C
authors.initials: AC
authors.lastname: van Rossum
authors.affiliation: Department of Cardiology and Radiology, Erasmus Medical Center, Rotterdam, the Netherlands.
authors.forename: Koen
authors.initials: K
authors.lastname: Nieman
authors.affiliation: Institute for Cardiovascular Imaging, Weill-Cornell Medical College, New York-Presbyterian Hospital, New York, New York.
authors.forename: James K
authors.initials: JK
authors.lastname: Min
authors.affiliation: Department of Medicine and Radiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Jonathon
authors.initials: J
authors.lastname: Leipsic
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Niels
authors.initials: N
authors.lastname: van Royen
authors.affiliation: Department of Cardiology, VU University Medical Center, Amsterdam, the Netherlands. Electronic address: p.knaapen@vumc.nl.
authors.forename: Paul
authors.initials: P
authors.lastname: Knaapen
mesh_terms: D000368:Aged; D017023:Coronary Angiography / Q000379:methods*; D023921:Coronary Stenosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D003331:Coronary Vessels / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D053805:Fractional Flow Reserve, Myocardial; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography; D015588:Observer Variation; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D061205:Vascular Calcification / Q000000981:diagnostic imaging / Q000503:physiopathology
keywords: coronary artery disease; coronary computed tomography angiography; fractional flow reserve