1. Cardiac CT
Shiva Roy FRACP
2008

2. 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 $
Perfusion scan $1000
Cardiologist / stress echo $500
Functional testing: 70-80% sensitivity and specificity in best hands. Up to 2% annual incidence of events in trial patients with negative stress echo’s – 20% 10 yr incidence i.e. high risk (we reassure!)
Expensive: 1 Cardiac death in Eastern Suburbs - Millions of lost revenue in taxes, millions in insurance payouts

3. 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
What about the asymptomatic 30 yr old smoker with a family history, LDL of 3.6 and HDL of1.2?
PBS guidelines do not take total risk into account
NCEP
Surely the early detection of plaque and commencement of lipid lowering therapy would have prevented some events. Clearly we need more sensitive screening to detect early plaque formation facilitating early introduction of lipid lowering therapy in at risk people. Coronary calcium has been identified as a way of defining a CAD equivalent.

4. 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
Technique discredited early on, levelled at the entrepreneurial approach of it’s introduction rather than on any scientific basis and in fact it has proven to be a very robust technique in identifying at risk population but not an at risk individual. N.B. – CTA not discredited for the same reason. Coronary Calcium scores are given in all patients undergoing CTA except graft patients and some stent patients (not necessary, have diagnosed obstructive disease)

6. New Guidelines From AHA

7. 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.

8. 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):
March 27, 2008

9. 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

10. 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
Successive generations of CT scanners have been applied to Cardiac imaging
This has resulted in Accelerated….
As a result the Diagnostic…..

11. Coronary Motion

12. 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
The problem with the heart is that it moves through multiple planes and we need to account for translational, rotational and accordian-type movements in attemting to create a still picture we can analyse.
Presently, selective coronary angiography is the gold standard in assessing coronary artery patency. The whole heart is covered throughout the imaging cycle, the Temporal resolution is 10msec which means a still image is created every .01sec. Spatial resolution is extremely high with flat plane imaging and can discriminate .01 of a mm.
We need to benchmark CT coronary angiography against this. To obtain a still frame we need a Detector array covering the whole heart – around 14cm, spatial resolution of 0.3mm which is about the threshold of clinical relevance and temporal resolution of msec which is sufficient to suppress all cardiac motion. We’re not quite there yet but we’re not far off

13. Technology 64 slice CT pivotal technology “Can Do”
Spatial resolution 0.35 mm – “isotropic”
Slice, dice, any angle, cross sectional analysis
Temporal resolution msec
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
64 slice CT is the pivotal technology that has brought CT coronary angiography to clinical relevance
..Spatial resolution of 0.35mm is probably at the threshold of clinical relevance and allows for isotropic”imaging. This means that the cube of information has identical X, Y and Z axes and therefor appears the same from any projection
..Temporal resolution of 65 to 200 msec depending on whether half segment or multisegment reconstruction
..Detector array 4 cm wide so the whole heart is covered in four rotations which takes 1.4cm. Practically each segment is scanned 2, 3 or 4 times so scan time on the GE machine is 6 seconds. Siemens detector array is about half the width so the scan time is twice as long….. Don’t believe everything you here.

14. Helical Scanning
Helical scanning involves continuous x-ray exposure and table movement to acquire the most image data in the shortest time.

15. Snapshot Pulse is most dose efficient
At Z location,
waiting for desired heart phase
NO XRAYS
Z location
Time

16. METHODS - CTA 0.5-0.625 mm slices Single Breath-hold Imaging
80 cc Non-ionic (IODINATED) contrast
Aggressive B blockade

17. Normal Study

18. 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

19. 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 49
Stenoses > 70%, per vessel 85 92 33 99
ACCURACY study. 232 pts. Chest pain syndromes. Low ppv due to low prevalence of disease in this gp.
PPV=positive predictive value
NPV=negative predictive value
Min J. Radiological Society of North America 2007; November 25-30, 2007; Chicago, IL.

20. 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 – mSv
Nuclear Imaging – 6-15 mSv

21. Case 1 - 43 male 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

22. Functional Test
Objectively negative stress echocardiogram – 13 minutes
However, vague left sided chest pain at peak exercise
“Is my heart OK ?”
CIA Mar 08

23. LAD
CIA Mar 08

24. 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

25. Volume rendered image of Coronary CT
Severe LAD and Diagonal branch stenosis

26. 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.

27. 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)

28. Assessment 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

29. Management 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 ?

30. Cardiovascular Risk Assessment
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

31. - 4 +7
+8 (assume still smoking) +1
13 (12%/10yrs)

32. Management 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

33. NHF Guidelines Known CHD, PVD or CVD AAA DM CRF
Familial Hyperlipidaemia
Absolute risk of >2%/yr

34. NHF Guidelines 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

36. 64 slice coronary CT angiography
Referred by GP June Calcium score 360

37. CT + Catheter Angiogram correlation

38. CT – Cardiac Applications
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

40. Open Bypass Grafts 40

41. Coronary aneurysms

42. Apical Thrombus and Infarction

43. Left Atrial Appendage Thrombus
Another interesting finding:
Filling defect/Thrombus in the left atrial appendage. (low flow is the cause of thrombis- AF patients)
? The function of the Appendages
(vestigial- left over – evolution)
Concern is that a part may break off and travel north and cause the patient to stroke

44. ASD

45. Patent Ductus ArteriosusAo

46. Pericardial Thickening

47. Pulmonary Veins

48. Placement of LV Lead

49. 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/non-coronary cardiac surgery
Possible Pulmonary embolus/aortic dissection

50. Triple Rule In

51. 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

53. Potential use of CT Coronary Angiography
Intermediate Risk
Low risk
High Risk
Asymptomatic?/atypical pain
No Investigation
or Functional testing
(Stress ECG/Echo/Nuclear)
Suspicious pain/Neg FT
Atypical pain/Pos FT
Poorly compliant with
Lifestyle or med Rx
angina, ECG +ve
Troponin +ve,
functional test +ve
MSCT
Mild atheroma
Moderate atheroma
Severe atheroma
Functional test
Medical therapy
No ischaemia
Ischaemia
Medical therapy
Angio / revascularisation
Risk as calculated by conventional vascular risk factors: Low<10%, intermediate 10-20%, High>20%