that for a calcium score of 1 to 400 (which means mild to
moderate amount of calcium deposits), a CCTA should
be performed.
However, the British Society of Cardiovascular
Imaging takes the view that CT calcium scoring is to
be used only as a backup if a patient is unsuitable for a
full CCTA. The reason is that studies comparing CCTA
with CT calcium scores show that the utility of using a
calcium score of 0 as an exclusion of underlying heart
artery disease would end up with misdiagnosis or further
testing in a significant proportion of patients, even in low-
risk groups.
Hence, from a cost perspective, CCTA is more cost-
effective compared to CT calcium scoring, leading to
faster diagnosis, fewer probes, lower cost, and better
outcomes. In 2015 a publication in Open Heart, a British
medical journal, showed that the implementation of the
UK guidelines in the University College London Hospital
led to a reduction in the average cost of the diagnostic
journey per patient and fewer investigations per patient
in order to confirm a diagnosis.
In recent years, data from many large studies have
shown data consistent with the UK guidelines. All this
shows that that CCTA is a safe and effective alternative
to stress testing in those with chest pain.
Heart scans versus prediction models
All these trials examined a population with a relatively
low heart artery disease prevalence. The probability
of heart disease for each individual was severely
overestimated by standard prediction models based
on formulas. Hence although the heart artery disease
prevalence in one of the trials, called the CRESCENT
trial, was 8 per cent, the predicted probability by
the widely used prediction model by Diamond and
Forrester was 45 per cent.
Likewise, the disease prevalence was 8.8 per cent
in another trial, PROMISE, but the average predicted
likelihood was 53 per cent. Even if newer risk prediction
tools were used as in the 2013 European Society
of Cardiology prediction model and was applied to
CRESCENT, it only lowered the probability from 45 to
37 per cent; still much higher than the actual 8 per cent
prevalence of heart artery disease. Hence, the current
disease prediction models significantly overestimated
disease burden.
Better test for women
There is substantial evidence to show that women
have higher rates of false-positive exercise stress tests
and nuclear stress tests as compared with men, and
hence there was a need to look for a better alternative.
As CCTA allows direct visualization of heart arteries,
this would reduce the unnecessary stress and additional
testing arising from false-positive tests. In ROMICAT-II,
women with chest pain who presented to the emergency
department and underwent CCTA benefitted from a
greater reduction in length of stay as compared to men.
In a sub-analysis of women in the CRESCENT trial, it
was shown that compared to stress testing, women who
underwent CCTA had higher chest pain resolution within
one year (40 per cent CCTA versus 22 per cent stress),
GlobalHealthAndTravel.com
underwent less additional diagnostic testing and had
lower downstream diagnostic costs.
What this meant was significant improvements in
processes of care and diagnostic efficiency for women
who underwent CCTA instead of conventional stress
testing. In women, sub-analysis of the PROMISE
trial showed that women derived greater prognostic
information from an abnormal CCTA than from an
abnormal stress test. In comparison, the prognostic
information from both testing strategies were similar
for men.
Making the best decision
The key practical take-home messages are:
• If you want faster diagnosis and less downstream
testing, current data favour the use of CCTA as the first
line choice for chest pain. In the UK, this has shown
faster diagnoses, fewer investigations, and lower costs
for diagnosis.
• If you want the best certainty about the likelihood of
underlying heart artery disease from non- invasive
testing, CCTA is the only non-invasive test which has
been able to demonstrate a consistent 100 per cent
negative predictive value for heart artery testing in
experienced centres; no other non-invasive test can
tell you with 100 per cent certainty that you do not
have heart artery disease.
• Compared to functional testing, CCTA is more likely to
result in resolution of chest pain symptoms, provide
better prognostic information and lead to better
outcomes. Hence, when you see your family doctor for
chest pain, you will be able to have better discussion
on what the most appropriate choice for you is.
• Not all CT scans are the same and the experience of
the centre is also very important. Recently, I saw a
patient who had a CCTA done in a hospital and was
advised to undergo invasive coronary angiogram
with a view to open up the heart arteries with balloon
angioplasty and stenting.
Dr Michael Lim
Senior Consultant
Physician/Cardiologist
MBBS, MRCP (UK), M
Med (Int Med), FAMS
(Cardiology), FRCP
(Edin)
She did not want to do so and was referred by her
family doctor to see me for further evaluation. I examined
images of the CCTA and was of the view that there were
artefacts that affected the accuracy of the scan. After
discussion of the various options, it was decided to use
another newest generation CT scan whose radiation
dose was extremely low to assess the heart arteries. To
the delight of the patient and her family, the scan showed
that there was no significant blockage of the heart
arteries and no further heart evaluation was required.
Therefore, should you ever require a CCTA, discuss
with your family doctor to send you to centres which
have new generation CT scanners and doctors who have
substantial experience in CCTA.
For enquiry or appointment, call +65 6931 8000
Visit us at:
MWH Medical Specialists Centre, 101 Irrawaddy Road,
#07-01 Royal Square Medical Centre
Singapore 329565
MARCH 2020
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