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Cardiac CT
Shiva Roy FRACP
2008
Why change current practise?
• Poor at predicting cardiac events
– 50% of first cardiac events are MI.
– 50% events occur in low to mod risk patients
– >50% patients with MI “average” lipids
• Functional testing inaccurate “So I’m going to live?”
• Expensive business!
– Hospital admission / angio $5000.00
– Perfusion scan $1000
– Cardiologist / stress echo $500
Lipid Management
• Frequently uncertain who to treat
• NCEP supports statins in high risk (>20% 10 yr)
• Moderate risk (10-20% 10yr) group challenging
– Akosah et al: Young pts mean age 50 presenting MI
• 70% in lower risk category and statin ineligible
• Early plaque detection / lipid lowering therapy
Coronary Calcification
• Misguided bias against technique
• Proven robust technique in identifying at risk
population
• Coronary Calcium Score >100 or >75th pecentile
identifies a CAD equivalent
New Guidelines From AHA
AHA – Circulation 2005
Given the evolving literature since the last
ACC/AHA Expert Consensus statement (2000),
current data indicate that CAD risk stratification is
possible with CAC measures.
Specifically, low CAC scores are associated with a
low adverse event risk, and high CAC scores are
associated with a worse event-free survival.
This recommendation to measure atherosclerosis
burden, in clinically selected intermediate–CAD
risk patients (eg, those with a 10% to 20%
Framingham 10-year risk estimate) to refine
clinical risk prediction and to select patients for
altered targets for lipid-lowering therapies.
Original Article
Coronary Calcium as a Predictor of Coronary
Events in Four Racial or Ethnic Groups
Robert Detrano, M.D., Ph.D., Alan D. Guerci, M.D., J. Jeffrey Carr, M.D., M.S.C.E.,
Diane E. Bild, M.D., M.P.H., Gregory Burke, M.D., Ph.D., Aaron R. Folsom, M.D.,
Kiang Liu, Ph.D., Steven Shea, M.D., Moyses Szklo, M.D., Dr.P.H., David A. Bluemke,
M.D., Ph.D., Daniel H. O'Leary, M.D., Russell Tracy, Ph.D., Karol Watson, M.D., Ph.D.,
Nathan D. Wong, Ph.D., and Richard A. Kronmal, Ph.D.
N Engl J Med
Volume 358(13):1336-1345
March 27, 2008
Conclusion
• The coronary calcium score is a strong
predictor of incident coronary heart
disease and provides predictive
information beyond that provided by
standard risk factors in four major racial
and ethnic groups in the United States.
No major differences among racial and
ethnic groups in the predictive value of
calcium scores were detected
Introduction to Coronary CTA
• Imaging technique accounting for cardiac motion
through ECG gating
– Early 1980’s conventional CT
– 1987 EBCT
– 1999 Multi Detector CT
• Accelerated progression in imaging capability
over past decade will continue into forseeable
future
• Diagnostic capability has at times preceded the
critical evaluation of clinical application
Technology
• Cardiac motion – Translational, Rotational and
Accordian-type movements
• Selective coronary angiography gold standard
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Whole heart covered, real time imaging
Temporal resolution of 10msec
Spatial resolution 100um
But
• Lumen only
• Limited angles
• No cross sectional reconstruction
Technology
• 64 slice CT pivotal technology
 Spatial resolution 0.35 mm – “isotropic”
 Slice, dice, any angle, cross sectional analysis
 Temporal resolution 45-200msec
 Detector array 4 cm wide
 Infinite Grey scale, image vessel wall, characterise
plaque
• “Can Do”
– Sensitivity and Specificity ~95% c.f. invasive
angiography, ~5% segments unevaluable
Helical Scanning
• Helical scanning involves continuous x-ray
exposure and table movement to acquire the most
image data in the shortest time.
Snapshot Pulse is most dose
efficient
At Z location,
Z location
waiting for desired
heart phase
NO XRAYS
Time
METHODS - CTA
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0.5-0.625 mm slices
Single Breath-hold Imaging
80 cc Non-ionic (IODINATED) contrast
Aggressive B blockade
Normal Study
Accuracy of Noninvasive CT
Angiography: Trial exclusions
• Technically inadequate scans not included in analysis
• Patient exclusion criteria
– Rapid heart rates
– Irregular heart beat/arrhythmias
– Renal dysfunction
– Contrast Allergies
– Beta-blocker intolerant
• Obesity limits interpretation
Diagnostic accuracy of CTA
Analysis
Sensitivity
(%)
Specificity
(%)
PPV
(%)
NPV
(%)
Stenoses > 50%, per
patient
93
82
62
97
Stenoses > 50%, per
vessel
84
91
51
98
Stenoses > 70%, per
patient
91
84
49
98
Stenoses > 70%, per
vessel
85
92
33
99
PPV=positive predictive value
NPV=negative predictive value
Min J. Radiological Society of North America 2007;
November 25-30, 2007; Chicago, IL.
Radiation Dose with CT
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EBCT – calcium scan – 0.7 mSv
MSCT – Calcium scan – 1.2 mSv
MSCT – Angiogram – 9-18 mSv
Dose Modulation – up to 47% savings
Coronary Angiogram – 2.1-2.3 mSv
Nuclear Imaging – 6-15 mSv
• 43 year old man commenced a new exercise
program
• Left side chest discomfort on exertion
• Cholesterol 6.0, LDL 3.6, HDL 1.3
• No smoking, diabetes, HT or family history
of IHD
• BMI 26 kg/m2
• Medications – nil
• Resting ECG – normal
• What next ?
CIA Mar 08
• Objectively negative stress
echocardiogram – 13 minutes
• However, vague left sided chest pain at
peak exercise
“Is my heart OK ?”
CIA Mar 08
LAD
CIA Mar 08
Case 2
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48 yr old man
Consistent exertional bilateral arm tightness
“like the compression of a blood pressure cuff”
Chol 7.8, LDL 5.1. Father and brother IHD in
their 50s. On no medical therapy at time of
presentation
• Negative Stress Echo after 12 minutes of Bruce
protocol. No symptoms with stress test
• Worrying symptoms and CV risk factors, but
negative functional test
• Volume rendered image of Coronary CT
Severe LAD
and Diagonal
branch stenosis
Outcome
• This patient had a concerning history and
risk factor profile. He declined the offer of
an invasive angiogram given his negative
stress test. He agreed to have a CT coronary
angiogram which detected severe proximal
LAD disease which required
revascularisation.
Case 3
37 yr old pastry chef- referred Aug 05
Sudden death of 40 yr old first cousin
Background
SVT 3 episodes over last 15 years
Ex smoker 1year (since age 20)
FH of IHD father CABG at 63
Chol 5.4, LDL 3.4, HDL 1.2, TG 1.9
Chol/HDL ratio 4.5
Overweight at 100kg (BMI 33)
SR 86bpm
BP 130/90
ECG
ECHO
Exercise stress test (echo assisted)
11.5 mins of Bruce protocol
Normal haemodynamic response
Limited by fatigue no CP
No ECG or ECHO evidence of ischaemia
Lifestyle changes Stay off cigarettes
weight loss
dietary and exercise advice
Further investigation ? (asymptomatic)
novel risk factors Hs CRP, Lp(a),
homocysteine
GTT
ambulatory BP monitor
? Sleep study
Pharmacological intervention ?
Assessment of 5-10 year risk of coronary
event
Framingham risk score (10 year risk)
NZ risk calculator ( 5 year risk)
Pharmacological intervention if risk
>2%/yr or 20%/10yrs
• -4
• +7
• +8 (assume still
smoking)
• +1
• +1
• 13 (12%/10yrs)
Aspirin…recommended when 10yr risk> 10%
per 1000 people treated per year
prevent 14 AMI at expense of 4 bleeds
Statins.. NHF
Risk > 20%/10yrs
PBS
subsidy ineligible
Known CHD, PVD or CVD
AAA
DM
CRF
Familial Hyperlipidaemia
Absolute risk of >2%/yr
Increased absolute risk: LDL > 4.0 or Chol > 6.0
+ any 2 or more risk factors
HDL< 1.0
FH
HT
Overweight
Smoking
IGT
Microalbuminuria
Age> 45
Referred by GP June 2006 Calcium score 360
CT – Cardiac Applications
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Coronary Calcification (CAS)
Non-invasive Coronary Angiography
Aortic Assessment (anuerysm, dissection)
Pulmonary Embolism
Pericardial disease
Congenital heart disease
Cardiac thrombi & tumor
Quantification cardiac anatomy & volumes, global
& regional function
• Venous Anatomy – Pulmonary and Coronary
veins pre-procedure
Open Bypass Grafts
Coronary aneurysms
Apical Thrombus and Infarction
Left Atrial Appendage Thrombus
ASD
Patent Ductus Arteriosus
PA
Ao
Pericardial Thickening
Pulmonary Veins
Placement
of
LV Lead
Appropriateness criteria for Cardiac CT
CCT/CMR writing group JACC 2006:48(7):1-21
• Appropriate/uncertain/inappropriate indications
for cardiac CT based on symptom
status/ECG/biomarkers/ability to exercise/pre-test
risk profile
• Pre PV isolation/BiV pacing
• Anomalous coronary anatomy/pericardial
disease/cardiac masses/cardiomyopathy/noncoronary cardiac surgery
• Possible Pulmonary embolus/aortic dissection
Triple Rule In
In the ER?
• High negative predictive value, therefore CT may help
avoid unnecessary hospital admissions, however…
• Patient preparation
• 24hr scan workup usually not logistically feasible
• Scanner availability
• Coronary physiology and other investiagations(ECG and
biomarkers) well validated for prognosis
• All coronary segments may not be visible
• Apparent non-flow limiting lesion potentially unstable
• “Triple rule out” –high radiation and contrast doses
• High volume centre usually provides high quality service
Potential use of CT Coronary Angiography
Intermediate Risk
Low risk
High Risk
No Investigation
or Functional testing
(Stress ECG/Echo/Nuclear)
Mild atheroma
Asymptomatic?/atypical pain
MSCT
Suspicious pain/Neg FT
Atypical pain/Pos FT
Poorly compliant with
Lifestyle or med Rx
Moderate atheroma
angina, ECG +ve
Troponin +ve,
functional test +ve
Severe atheroma
Functional test
Medical therapy
No ischaemia
Medical therapy
Ischaemia
Angio / revascularisation
Risk as calculated by conventional vascular risk factors: Low<10%, intermediate 10-20%, High>20%