3 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)
4 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.
5 64-Slice CTIt 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.
6 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
7 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 imagingFrom Journal of Nuclear Medicine Vol. 47 No
8 Possible use of CTA in screening symptomatic patients Journal of Nuclear Medicine Vol. 47 No
9 Comparison of different Screening tests SensitivitySpecificityPPVNPVCTA89% (76-99)96% (95-97)76% (56-88)99% (96-100)Nuc Med Spect70-80%Stress EchoETT60-65%70-75%Cardiac Cath100%
10 Contraindications to Multislice CT Angiogram AbsoluteRapid heart rate, Atrial fib, frequent PVC’sPregnancyExtensive 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 secondsContraindication to IV contrast, beta-blocker or nitrates.RelativeHigh 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.
11 Risk of MSCT coronary False positives and negatives Radiation exposure Better rate than most noninvasive stress tests.Radiation exposureComparable to nuc med stressRisk is highest for young women
12 “Estimating the risk of Cancer Associated with Radiation Exposure from 64-Slice CT Coronary Angiography” JAMA 7/07Used 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.
13 Estimated Relative Risks of Attributable Cancer Incidence Associated With a Single Computed Tomography Coronary Angiography ScanaEinstein, A. J. et al. JAMA 2007;298:Copyright restrictions may apply.
14 Lifetime Attributable Risk of Cancer Incidence From a Single Computed Tomography Coronary Angiography (CTCA) ScanEinstein, A. J. et al. JAMA 2007;298:Copyright restrictions may apply.
16 Doses From the 8 Computed Tomography Coronary Angiography Protocols Einstein, A. J. et al. JAMA 2007;298:Copyright restrictions may apply.
17 Effective Radiation Doses for Various Tests Bone Density mSvCXR: mSvMammogram: mSvCT of the head: 2 mSvCT colonoscopy 5 mSvCT of the abdomen: mSvStress Gated Myocardial Perfusion Scan SPECT: mSvCT chest: mSvMSCT angiogram: mSv (MEN) mSv (w)Can be reduced 40% if ECG controlled X-ray tube current modulation is used.Coronary angiography: mSvCT chest/abd/pelvis: mSvDose allowed for radiological personnel: 20 mSv/year
18 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 radiationThe CTA is equivalent to about 4.5 to 6 years without modulation.A Chest/abd/pelvis is equivalent to 10.5 years.
19 Comparative Costs Table 1. Costs Used in Analysis, 1996 U.S. Dollars* CT angiogram 1500Positron emission tomography 1500Single-photon emission computed tomography 475 (NUC MED SPECT)Stress echocardiography 265Planar thallium imaging 221Exercise electrocardiography 110Coronary 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, 824Myocardial infarction: single admission 7415Cardiac catheterization with angiography 1810Percutaneous transluminal coronary angioplasty 11, 685 (average of 1- and 2-vessel procedures)4 May 1999 · Annals of Internal Medicine · Volume 130 · Number 9
20 ConclusionMSCT 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.
21 ConclusionsRadiation 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.