Cardiovascular Journal of Africa: Vol 28 No 6 (November/December 2017)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 1, January/February 2018 16 AFRICA
Value of transluminal attenuation gradient of stress
CCTA for diagnosis of haemodynamically significant
coronary artery stenosis using wide-area detector CT in
patients with coronary artery disease: comparison with
stress perfusion CMR
Hee Yeong Kim, Hwan Seok Yong, Eung Ju Kim, Eun-Young Kang, Bo Kyoung Seo
Abstract
Introduction: This study aimed to evaluate the value of
transluminal attenuation gradient (TAG) of stress coronary
computed tomography angiography (CCTA), using a wide-
area detector CT in patients with coronary artery disease,
compared to stress perfusion cardiac magnetic resonance
(CMR) imaging.
Methods: This prospective study from May 2012 to January
2015 included 21 patients with moderate coronary stenosis
on invasive coronary angiography. All patients underwent
adenosine stress single-shot CCTA with a rest CCTA scan
using a wide-area detector CT. Coronary artery stenosis was
evaluated on both stress and rest CCTA images, and TAG was
manually obtained for all vessels. Stress perfusion CMR was
used as a reference standard. A TAG cut-off value of –15.1
HU/10 mm was applied for diagnosing haemodynamically
significant stenosis. The diagnostic accuracies of TAG and
CMR were estimated and compared.
Results: TAG of stress CCTA in all coronary arteries had
a sensitivity, specificity, and positive and negative predic-
tive values of 90.5, 90.0, 86.4 and 93.1%, respectively.
Corresponding values for TAG of rest CCTA in all coronary
arteries were 42.9, 83.3, 64.3 and 67.6%, respectively, whereas
those for TAG of coronary arteries with moderate stenosis
on stress CCTA were 93.3, 100, 100 and 92.3%, respectively.
Mean effective radiation doses for stress and rest CCTA were
10.6 ± 2.6 mSv and 2.3 ± 1.3 mSv, respectively.
Conclusions: TAG of CCTA provided high diagnostic accu-
racy for detecting haemodynamically significant coronary
artery stenosis. TAG of stress CCTA was more diagnosti-
cally accurate, especially in coronary arteries with moderate
stenosis.
Keywords: coronary artery disease, transluminal attenuation
gradient, computerised tomography, magnetic resonance imaging
Submitted 25/4/16, accepted 1/5/17
Cardiovasc J Afr 2018; 29: 16–21
DOI: 10.5830/CVJA-2017-026
Coronary computed tomography angiography (CCTA) is
increasingly used as a non-invasive diagnostic imaging tool
for the detection and exclusion of coronary artery disease
(CAD).1,2 However, a well-recognised limitation of CCTA is
its moderate ability to assess the haemodynamic significance
of a given coronary stenosis.3 Other modalities, such as single-
photon emission computerised tomography (SPECT), cardiac
magnetic resonance (CMR) imaging, invasive fractional flow
reserve (FFR), CT-derived computed fractional flow reserve
(CT-FFR), or CT myocardial perfusion (CTP) can predict
haemodynamically significant coronary artery stenosis or
myocardial ischaemia. However, CTP imaging may require
additional iodinated contrast and radiation exposure,4,5 and the
analysis of CT-FFR data requires a large amount of time on
a parallel supercomputer,6 even though these modalities were
developed in an attempt to improve the diagnostic accuracy of
CCTA.
Recently, the transluminal attenuation gradient (TAG),
defined as the contrast opacification gradient along the length
of a coronary artery on CCTA, has been suggested as a tool for
detecting haemodynamically significant coronary artery stenosis.
TAG combines anatomical and functional information to enable
appropriate therapeutic decisions regarding CAD. Preliminary
data suggest that TAGprovides additional functional information
to CCTA.7,8 This method may represent a simple and useful test
to differentiate individuals who will or will not benefit from
revascularisation.
Choi et al.8 reported that TAG could provide information
about the functional significance of coronary artery stenosis.
However, that study was performed with a 64-slice multi-detector
row scanner. Although a subsequent study was performed with a
Department of Radiology, Kangnam Sacred Heart Hospital,
Hallym University College of Medicine, Seoul, Korea
Hee Yeong Kim, MD, PhD
Department of Radiology, Korea University Guro Hospital,
Korea University College of Medicine, Seoul, Korea
Hwan Seok Yong, MD, PhD,
Eun-Young Kang, MD, PhD
Division of Cardiology, Cardiovascular Centre, Korea
University Guro Hospital, Korea University College of
Medicine, Seoul, Korea
Eung Ju Kim, MD, PhD
Department of Radiology, Korea University Ansan Hospital,
Korea University College of Medicine, Seoul, Korea
Bo Kyoung Seo, MD, PhD