The document discusses advancements in cardiac CT, particularly 320-slice coronary CT angiography, which provides detailed, noninvasive imaging of coronary artery disease (CAD) and is shown to correlate well with invasive coronary angiography. It highlights the prognostic value of plaque composition detected by CT and its ability to improve patient outcomes, particularly in emergency situations. The paper advocates for a shift in focus from lumen stenosis to a comprehensive assessment of CAD and its implications for treatment and patient management.

1. WHAT IS NEW IN CARDIAC CT? IN SEARCH OF THE COMPREHENSIVE AND
CONCLUSIVE HEART SCAN

2. Review Article
According to World Health Organization statistics for
2007, cardiovascular deaths account for 33.7% of all
deaths worldwide, whereas cancer represents 29.5%, other
chronic diseases, injury and communicable diseases
contribute to 26.5%, 7%, and 4.6%, respectively [1].
Considering the fact that cardiovascular deaths top the list,
it would be useful to have a perfect diagnostic test to show
the disease clearly in its extent and nature. However, the
current noninvasive tests of ECG, Echo and TMT are
indirect means of judging the presence of significant
Coronary artery disease (CAD) and may even be
inconclusive.
In our study of patients with mildly positive TMT (CSI
2010) 85% of patients had CAD, majority of who had soft
plaques.
Invasive Coronary angiography (ICA) the gold
standard for coronary anatomy has had a profound impact
on the diagnosis and management of ischemic heart
disease, setting up the potential for both surgical and
percutaneous coronary revascularization and the
foundation for contemporary myocardial reperfusion
therapy. The enormity of the significance of ICA and how
it has completely revamped cardiovascular medicine in the
past four decades cannot be adequately emphasized.
Although the value of ICA remains unquestioned, it
depicts the coronary artery as a simple two-dimensional
projection of the lumen. Unfortunately, the silhouette or
“luminogram” is a relatively poor representation of
coronary anatomy and a limited standard on which to base
WHAT IS NEW IN CARDIAC CT? IN SEARCH OF THE COMPREHENSIVE AND
CONCLUSIVE HEART SCAN
Rochita Venkataramanan
Senior Consultant Radiologist, Apollo Hospital, 21, Greams Lane, Chennai 600 006, India.
E-mail:rochitav@gmail.com
Coronary CTAngiography (CT) with its noninvasive cross sectional information has seen remarkable growth in
recent years. With the introduction of the new generation scanners, like the 320-slice CT, it has risen to a whole
new level. Percent diameter stenosis determined with the use of 320-slice CT shows good correlation with
Invasive catheter angiogram (ICA) without significant underestimation or overestimation. Plaque composition
on CT regardless of lesion severity has emerged as a strong predictor of major cardiac events. The percentage
stenosis mismatch between CT and ICA can be explained by the 2 dimensional nature of ICA and its
interpretive inconsistencies. In the upcoming years, we need to evolve from focusing on lumen stenosis to a
comprehensive assessment of CAD and its impact on patient outcome.
Key words: 320 slice, CT Angiography accuracy, Coronary artery plaque composition, CABG, Percent
stenosis disagreement.
therapeutic decisions [2]. It is also invasive and requires
an additional stress test to add functional information to
judge the significance of a stenotic segment.
Coronary CT Angiography (CT) with its noninvasive
cross sectional information has seen remarkable growth
in recent years. With the introduction of the new
generation scanners CT has risen to a whole new level.
The 320 slices is among these prestigious high definition
scanners with wide-area detectors able to scan 16 cm of
the body in a single rotation (Fig 1).
320 SLICE MAKES CORONARY CT SAFER,
MORE COMFORTABLE AND ACCURATE
Dewey, et al [3] compared the 320 slice CT with ICA
in a head to head pilot study. They showed that whole-
heart coronary 320-slice CT significantly reduces the
effective radiation dose compared with catheter
angiogram. 320-slice CT now makes it possible to cover
the whole heart in a single CT snapshot. This approach
can reduce the radiation exposure by 4 to 5 fold because it
avoids the 400% to 500% overlapping rotations for
helical cardiac CT (over-scanning) and the extra 2
rotations necessary at the beginning and end of CT scans
(over ranging) that were previously necessary in most
cases. The per-patient sensitivity and specificity for 320-
slice CT compared with ICA were 100% and 94%
respectively. Percent diameter stenosis determined with
the use of 320-slice CT showed good correlation with ICA
(P ≤0.001) without significant underestimation or
Apollo Medicine, Vol. 8, No. 3, September 2011 200

3. Review Article
201 Apollo Medicine, Vol. 8, No. 3, September 2011
overestimation. Comparison of 320-slice CT with ICA
revealed a significantly smaller effective radiation dose
(4.2 mSv for CT vs. 8.5 mSv for ICA) and amount of
contrast agent required (median 80 ml for CT vs. 111 mL
for ICA P≤0.001) for 320-slice CT. The majority of
patients (87%) indicated that they would prefer CT over
ICA for future diagnostic imaging (P≤0.001).
PROGNOSTIC VALUE OF CT ANGIOGRAPHY
FOR MAJOR ADVERSE CARDIAC EVENTS:
SCORING OVER THE CLINICAL RISK MODEL
While it is exciting to produce exquisitely beautiful CT
images of CAD, the clinical usefulness of CT and the
concern whether CT actually improves patient outcomes
is an issue which needs to be resolved. Some authors feel
threatened by the enthusiasm for and proliferation of
unproven screening tests. Several recent studies have
addressed this concern.
Vincenzo Russo, et al [4] performed CT for a total of
441 patients with suspected CAD. Patients were followed
up as to the occurrence of hard cardiac events (cardiac
death, nonfatal myocardial infarction, and unstable angina
requiring hospitalization). 67.3% patients had CAD.
During a mean follow-up of 31 months 44 hard cardiac
events occurred in 40 patients. Calcium scoring showed a
statistically significant incremental prognostic value as
compared to a baseline clinical risk model (P≤0.018),
whereas CT angiography provided an additional
incremental prognostic value as compared with a baseline
clinical risk model plus calcium scoring (P≤0.016).
However, plaque composition (calcified versus soft and/or
mixed plaques) and the presence of soft or mixed plaques,
regardless of lesion severity, was found to be the strongest
predictor of events as a potential marker of plaque
vulnerability (P≤0.0001). During follow-up, an excellent
prognosis was noted in patients with normal coronary
arteries on CT.
CT provides independent and incremental prognostic
information as compared to baseline clinical risk factors
and calcium scoring in patients with suspected CAD [5,6].
CT ANGIOGRAPHY VALUE IN THE EMERGENCY
ROOM. NO MORE GUESSING
Arthur Nasis, et al [7] showed that when CT is used in
the ER for patients with chest pain with low to intermediate
risk, those patients without overt plaque can be immediately
discharged from the hospital. Patients with non-obstructive
plaque and mild to moderate stenosis can be discharged after
a negative 6 hour troponin level, and patients with severe
stenosis need to be admitted to the hospital for further
management.At follow-up, there were no deaths or cases of
acute coronary syndrome and the rate of readmission to the
hospital because of chest pain was higher in those patients
who had not had a CT. Mean length of stay was lower with
Fig.1 The contours of the arteries are sharper and rounder on the 320 slice CT as compared to the 64 slice which shows a
flattening of the artery due to artefact between the subsequent scanned segments (yellow lines).

4. Review Article
Apollo Medicine, Vol. 8, No. 3, September 2011 202
those patients who had a CT. Tailoring troponin
measurement to CTfindings allows safe and early discharge
of patients resulting in reduced length of stay.
CT ANGIOGRAPHY USEFULNESS FOR
PERCUTANEOUS CORONARY INTERVENTION
AND THROMBOLYSIS
Coronary artery lesions that are more than 2 cm in
length, across an excessively angulated segment, with
heavy calcification, across ostia or bifurcations, with
irregular surfaces and adherent thrombi, past tortuous
segments or those that are totally occluded are considered
complex and have limited success after stenting [8]. It is
therefore important to identify these lesions. Brett M
Wertman, et al [9] demonstrated that CT is quite capable
of identifying these Type C complex lesions that are
associated with higher contrast use and greater procedure
length during PCI. This comes as no surprise and is a
foregone conclusion given the cross sectional nature of
CT (Fig 2).
Post-procedural myocardial injury is associated with
thick soft plaques as detected by CT [10]. Those patients
who had a large soft plaque in the lesion being stented
demonstrated a rise in the troponin T levels after the
procedure. Plaque analysis by CT would therefore be a
useful method for predicting post-procedural myocardial
injury after percutaneous coronary intervention.
Makoto Yamashita, et al [11] demonstrated that in
patients with Acute MI, CT can differentiateAngiographic
Fig.2 (a) Coronary plaque with partly soft and part calcific nature (mixed plaque) in the mid LAD. (b) The 3D image gives the
relation of the stenotic segment to side branches as well as the curvature of the artery. (c) The lesion length and vessel
diameter can be measured. (d) The myocardium Sagittal view reveals a dark area in the suendocardium of the anterior
wall representing ischaemia.

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203 Apollo Medicine, Vol. 8, No. 3, September 2011
TIMI grade 3 (normal) from TIMI grade 2 (sluggish) flow
by comparing the density of contrast at the distal end of the
thrombolysed artery with that proximal to the stenotic
lesion. CT number distal /CT number proximal should be
more than 0.54 for TIMI 3. CT can be used to assess
coronary reperfusion noninvasively after thrombolysis.
PLAQUE REGRESSION ASSESSMENT BY CT
ANGIOGRAPHY
The discovery of early CAD on CT would be futile if
these could not be resolved by medication. However
several multicenter, randomized lipid-lowering trials
using both catheter angiographic and clinical assessment
showed a negligible improvement ((1 to 3%) of luminal
caliber on ICA. Yet these same studies yielded 25% to
75% reduction in acute events, including myocardial
infarction [12-14]. This points to the fact that the benefits
of lipid-lowering therapy are derived by stabilization of
lipid-rich plaques, not changes in angiographic lumen
size. Regression in the size of the plaque can be well
assessed by CT.
Kaori Inoue, et al suggest that the use of statins even at
a low dose may result in significant changes in plaque
morphology on CT and an absolute decrease in plaque
volume without significant change in lumen size and when
the changes in lipid profile are not statistically significant.
This suggests that the changes in the plaque morphology
may even occur with relatively less robust changes in the
lipid profile, and may occur early after statin use [15].
STRESS MYOCARDIAL CT PERFUSION IS HERE
Stress myocardial computed tomography perfusion
(CTP) is a novel examination that provides both anatomic
and physiological information (i.e., myocardial
perfusion). Multiple single-center studies have
established the feasibility of stress myocardial CTP.
Furthermore, it has been illustrated that a combined
CCTA/CTP protocol improves the diagnostic accuracy to
detect hemodynamic significant stenosis as compared
with CTA alone. Stress and reversible myocardial
perfusion deficit measured by CT using a visual semi
quantitative approach and a visually guided software-
based approach show strong similarity with SPECT
[16,17].
CT AND ICA DISAGREEMENT ON PERCENTAGE
STENOSIS. “NEVER THE TWAIN SHALL MEET”
Despite good sensitivity and specificity for detecting
significant coronary artery disease in patients,
disagreement on individual coronary arterial stenosis
severity is common between CT and the current “gold
standard” ICA. This is true for IVUS and histopathology
as well, which also do not correlate with ICA. Catheter
angiogram readings vary from doctor to doctor and such
inconsistencies as well as the modality’s limitations as a 2-
dimensional technique are important reasons for
discrepant results between CT and ICA that are less
acknowledged.
CT and ICA are fundamentally different technologies.
Expecting good agreement on the degree of lumen
narrowing is rather unrealistic. Importantly, percentage of
stenosis is of uncertain relevance for patient outcome.
Arbab-Zadeh and Hoe clearly point out that assessment of
total (calcified and non-calcified) coronary atherosclerotic
plaque burden, number of lesions and location, as well as
plaque characterization, show strong promise for superior
prognostic impact than mere lesion quantification and
thus, deserve more of our attention. In the upcoming years,
we need to evolve from focusing on lumen stenosis to a
comprehensive assessment of CAD and its impact on
patient outcome [18].
For example a glass cylinder that is filled with marbles
and then completely filled with ink hides the presence of
the marbles within and appears to be filled only with ink.
Similarly, complex CAD like the marbles can be
completely hidden by the dense contrast within the
coronary artery on ICA. However if one were to section
the cylinder and look within with CT the marbles would be
clearly visible as would the real amount of narrowing
within the cylinder. This is how CT is a more accurate
measure of degree of stenosis and presence of CAD than
ICA (Fig.3).
Fig.3 (a) Coronary CT reveals a very short intraluminal
complex filling defect in this symptomatic patient. (b)
However Catheter angio reveals a subtle irregularity
only on very careful scrutiny. (c&d) explain how an
intraluminal plaque causing an non concentric stenosis
can be missed on the 2 D projections of the catheter
anglogram (taken from reference 2).

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Apollo Medicine, Vol. 8, No. 3, September 2011 204
In our study “Coronary artery bypass graft patency
relationship to target artery stenosis and its effect on native
vessels, a CTA analysis” (presented at the 8th
International Congress on Coronary Artery Disease 2009)
we found that not only does ICA underestimate disease, it
can also overestimate stenosis due to complex plaque
morphology and angiographic projections making
borderline stenosis appear tighter. This also happens due
to an interpretive error associated with variations in the
way ICA is read by different doctors. As a result grafts
which were thought to have been placed on 80% stenosis
actually could at times land on a 60% stenosis. This sets up
a chronic competitive flow war between the graft and the
native coronary artery causing graft failure and
progression of disease in the native artery rapidly
rendering vessels difficult for future percutaneous or
surgical intervention (Fig.4).
CONCLUSION
Coronary CT Angiography in the present era of high
end scanners like the 320 slice CT has evolved into an
ideal test which can consistently and clearly image the true
coronary arterial stenosis severity, a detailed depiction of
the atheroma causing this, the downstream effect on the
myocardium, functionality of the heart with minimum
contrast dose and radiation in a short time with no patient
discomfort. CT proves that regardless of lesion severity
the presence of soft and mixed plaques can cause
significant cardiovascular events scoring over a clinical
risk model. CT can be used in the emergency room to
actually look into the coronary arteries and decide who
needs to be hospitalized for an ongoing cardiac event. A
safe and early discharge can be confidently decided for
those patients who do not have a cardiac event. CT may be
able to demonstrate significant benefit at lowered doses of
statins by showing a reduction in plaque volume.
By the demonstration of the true percentage of
stenosis, CABG based on CT would ensure graft
longevity.
Many authors believe that this is just scratching the
surface of the true potential of this new test and as the
machines advance, a more accurate and clear
understanding is evolving in the field of cardiology.
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Fig.4 The 3D image on the left shows the LAD and LCx
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