cardiac ct shiva roy fracp 2008. why change current practise? poor at predicting cardiac events...
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Cardiac CTCardiac CT
Shiva Roy FRACPShiva Roy FRACP
20082008
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 2005Given 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 MedVolume 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– 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 technologySpatial resolution 0.35 mm – “isotropic”Slice, dice, any angle, cross sectional analysisTemporal 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
Z loca
tion
Time
At Z location, waiting for
desired heart phase
NO XRAYS
METHODS - CTAMETHODS - CTA
• 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
Min J. Radiological Society of North America 2007; November 25-30, 2007; Chicago, IL.
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 valueNPV=negative predictive value
Radiation Dose with CT
• 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
CIA Mar 08LAD
Case 2• 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.
37 yr old pastry chef- referred Aug 05Sudden death of 40 yr old first cousinBackground 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)
Case 3
SR 86bpmBP 130/90ECGECHOExercise 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 factorsHDL< 1.0FHHTOverweightSmokingIGTMicroalbuminuriaAge> 45
Referred by GP June 2006 Calcium score 360
• 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
CT – Cardiac ApplicationsCT – Cardiac Applications
Open Bypass Grafts
Coronary aneurysms
Apical Thrombus and Infarction
Left Atrial Appendage Thrombus
ASD
Patent Ductus Arteriosus
Ao
PA
Pericardial Thickening
Pulmonary Veins
Placementof
LV Lead
Appropriateness criteria for Cardiac CTCCT/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/non-coronary 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 AngiographyIntermediate
RiskLow risk High Risk
No Investigationor Functional testing
(Stress ECG/Echo/Nuclear)MSCT
Suspicious pain/Neg FTAtypical pain/Pos FT
Poorly compliant withLifestyle or med Rx
angina, ECG +veTroponin +ve, functional test +ve
Mild atheroma Moderate atheroma Severe atheroma
Functional test
No ischaemia Ischaemia
Medical therapy Angio / revascularisation
Medical therapy
Risk as calculated by conventional vascular risk factors: Low<10%, intermediate 10-20%, High>20%
Asymptomatic?/atypical pain