Download Cardiac Disease Assessment with CT –Update

Multislice CT Coronary
Angiography
Pete Newcomer
11/07
Types of Coronary CT
imaging
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MSCT (multislice CT) : A new form of
cardiac imaging. This is a way to measure
obstruction similar to a cardiac
catheterization. It is NOT a functional test.
Coronary Calcium Scoring: calcium scoring
for risk assessment. This is for
asymptomatic patients and is not yet
recommended as a routine screen. (CCS
can be normal in 5% of patients who have
myocardial infarcts)
MSCT Coronary
Angiography: Details
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Initial studies 5-10 years ago used 4-slice MSCT.
Then came 16-slice (we still use these in some
centers) and now 64-slice MSCT is arriving in just the
last few years.
The 64-slice CT is the current standard (approved in
2004). We have one at the UW and one at the VA.
Meriter has a dual head 64-Slice CT. (can handle
faster heart rates)
256-slice CT angiograms are just starting to be
evaluated.
64-Slice CT
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It now has a spatial resolution of 0.4 by 0.4 by 0.4 mm.
Which is adequate to view all of the main coronary
arteries. (0-5% inevaluable in different studies)
CT images that are used come from mid to end
diastole due to relative motion free period. CT scans
the entire cardiac cycle but uses ECG after the fact to
pull the images from mid to end diastole only.
IV contrast is used.
Heart rate needs to be less than 70 bpm so betablockers are used (protocol). (unless using dual head)
Dilating of vessels helps so NTG is used by protocol at
the UW.
MSCT Coronary
Angiography Accuracy
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Accuracy of testing:
 For 64 slice CTA:
(for clinically significant occlusions, >50%)
• Sensitivity: 89 %
• (If cardiac cath positive (gold standard), CTA will be
positive 89% of the time)
• Specificity: 96%
• (if cath negative, the CTA will not find it 96% of the time.)
• Negative Predictive Value: 99%
• (if negative CTA, cath is negative 99% of time)
• Positive Predictive Value: 78%
• (if positive CTA patient has positive cath 78% of the time)
• Clinical Cardiology vol. 30 , 9/07
Clinical Applications of CTA
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•Screening: no application
•Diagnosis of CAD
 Intermediate likelihood of disease **
 After equivocal/discordant stress imaging **
 Coronary anomalies
 Before valvular surgery
 Nonischemic vs. ischemic cardiomyopathy
 Acute chest pain (our ED/Cards starting a pilot study soon)
 Bypass graft patency/location (images of transplanted
arteries and veins are much better)
•Risk stratification (known CAD)
 After equivocal/discordant stress imaging
• From Journal of Nuclear Medicine Vol. 47 No. 7 1107-1118
Possible use of CTA in screening symptomatic
patients
Journal of Nuclear Medicine Vol. 47 No. 7 1107-1118
Comparison of different
Screening tests
Test
Sensitivity
Specificity
PPV
NPV
CTA
Nuc Med
Spect
Stress
Echo
ETT
Cardiac
Cath
89% (76-99)
96% (95-97)
76% (56-88)
99% (96-100)
70-80%
70-80%
70-80%
70-80%
60-65%
100%
70-75%
100%
Contraindications to
Multislice CT Angiogram
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Absolute
 Rapid heart rate, Atrial fib, frequent PVC’s
 Pregnancy
 Extensive calcification (often a CCS is done first and if
very high, > 1000, the CTA is not done). We do this
screen here.
 Unable to hold breath for 20 seconds
 Contraindication to IV contrast, beta-blocker or
nitrates.
Relative
 High BMI: for e.g. if BMI < 25 the sens, spec, PPV
and NPV are 100%, declines with weight.
 Younger patients especially if female due to increased
risk of excessive radiation.
Risk of MSCT coronary
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False positives and negatives
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Better rate than most noninvasive
stress tests.
Radiation exposure
Comparable to nuc med stress
 Risk is highest for young women
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“Estimating the risk of Cancer Associated with Radiation
Exposure from 64-Slice CT Coronary Angiography”
JAMA 7/07
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Used most recent information about health
effects of radiation to estimate lifetime
attributable risk (LAR) of 64-Slice CTA.
Concluded that CTCA was associated with
a nonnegligible LAR of cancer especially in
women, younger patients and for combined
cardiac and aortic scans.
Estimated Relative Risks of Attributable Cancer Incidence Associated With a Single Computed
Tomography Coronary Angiography Scana
Einstein, A. J. et al. JAMA 2007;298:317-323.
Copyright restrictions may apply.
Lifetime Attributable Risk of Cancer Incidence From a Single Computed Tomography Coronary
Angiography (CTCA) Scan
Einstein, A. J. et al. JAMA 2007;298:317-323.
Copyright restrictions may apply.
Lifetime attributable risk estimates of all-cancer incidence per 100 000 persons exposed to
a single 100-mGv dose to all organs
Einstein, A. J. et al. Circulation 2007;116:1290-1305
Copyright ©2007 American Heart Association
Doses From the 8 Computed Tomography Coronary Angiography Protocols
Einstein, A. J. et al. JAMA 2007;298:317-323.
Copyright restrictions may apply.
Effective Radiation Doses
for Various Tests
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Bone Density
CXR:
Mammogram:
CT of the head:
CT colonoscopy
CT of the abdomen:
Stress Gated Myocardial Perfusion Scan SPECT:
CT chest:
MSCT angiogram:
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0.01 mSv
0.02 mSv
0.7 mSv
2 mSv
5 mSv
10 mSv
10-11 mSv
13 mSv
15 mSv (MEN)
21 mSv (w)
Can be reduced 40% if ECG controlled X-ray tube current
modulation is used.
Coronary angiography:
CT chest/abd/pelvis:
Dose allowed for radiological personnel:
6-30mSv
35 mSv
20 mSv/year
What does that mean?
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Radiation sickness occurs at 1000 mSv,
death within a few weeks at 10,000 mSv.
10 mSv is equivalent to about 3 years of
“background radiation”.
So a mammogram is equivalent to about 3
months worth of background radiation
The CTA is equivalent to about 4.5 to 6
years without modulation.
A Chest/abd/pelvis is equivalent to 10.5
years.
Comparative Costs
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Table 1. Costs Used in Analysis, 1996 U.S. Dollars*
CT angiogram 1500
Positron emission tomography 1500
Single-photon emission computed tomography 475 (NUC MED
SPECT)
Stress echocardiography 265
Planar thallium imaging 221
Exercise electrocardiography 110
Coronary artery bypass surgery: 1- and 2-vessel 32, 390 (average
of 1- and 2-vessel procedures)
Coronary artery bypass surgery: 3-vessel and left main 32, 824
Myocardial infarction: single admission 7415
Cardiac catheterization with angiography 1810
Percutaneous transluminal coronary angioplasty 11, 685 (average
of 1- and 2-vessel procedures)
4 May 1999 · Annals of Internal Medicine · Volume 130 · Number 9
Conclusion
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MSCT is an new modality to assess coronary
disease. It has been predicted that CTCA may
emerge as the diagnostic test of choice for
patients with intermediate pretest probability of
disease. (JAMA vol 298, No. 3)
It is a rapidly advancing field and we will soon
be seeing it used more frequently. The ED may
be the first place used due to the ability to
rapidly evaluate chest pain.
Conclusions
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Radiation risk is real but is comparable to other
tests that we order and with careful patient
selection and improved scanners can be
reduced.
MSCT role in our outpatient clinic is not yet
clear but for patients with chest pain and
equivocal testing it may play a role.