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