Multislice CT Coronary Angiography

Pete Newcomer

11/07

Types of Coronary CT imaging 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 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

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 beta-

blockers are used (protocol). (unless using dual head) Dilating of vessels helps so NTG is used by protocol at

the UW.

MSCT Coronary Angiography Accuracy 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

•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

Test Sensitivity Specificity PPV NPV

CTA 89% (76-99) 96% (95-97) 76% (56-88) 99% (96-100)

Nuc Med Spect

70-80% 70-80%

Stress Echo

70-80% 70-80%

ETT 60-65% 70-75%

Cardiac Cath

100% 100%

Comparison of different Screening tests

Contraindications to Multislice CT Angiogram 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

False positives and negativesBetter rate than most noninvasive

stress tests. Radiation exposure

Comparable to nuc med stressRisk is highest for young women

“Estimating the risk of Cancer Associated with Radiation Exposure from 64-Slice CT Coronary Angiography”JAMA 7/07

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.

Copyright restrictions may apply.

Einstein, A. J. et al. JAMA 2007;298:317-323.

Estimated Relative Risks of Attributable Cancer Incidence Associated With a Single Computed Tomography Coronary Angiography Scana

Copyright restrictions may apply.

Einstein, A. J. et al. JAMA 2007;298:317-323.

Lifetime Attributable Risk of Cancer Incidence From a Single Computed Tomography Coronary Angiography (CTCA) Scan

Copyright ©2007 American Heart Association

Einstein, A. J. et al. Circulation 2007;116:1290-1305

Lifetime attributable risk estimates of all-cancer incidence per 100 000 persons exposed to a single 100-mGv dose to all organs

Copyright restrictions may apply.

Einstein, A. J. et al. JAMA 2007;298:317-323.

Doses From the 8 Computed Tomography Coronary Angiography Protocols

Effective Radiation Doses for Various Tests Bone Density 0.01 mSv CXR: 0.02 mSv Mammogram: 0.7 mSv CT of the head: 2 mSv CT colonoscopy 5 mSv CT of the abdomen: 10 mSv Stress Gated Myocardial Perfusion Scan SPECT: 10-11

mSv CT chest: 13 mSv MSCT angiogram: 15 mSv (MEN)

21 mSv (w) Can be reduced 40% if ECG controlled X-ray tube current

modulation is used. Coronary angiography: 6-30mSv CT chest/abd/pelvis: 35 mSv Dose allowed for radiological personnel: 20

mSv/year

What does that mean?

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

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

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

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.