2Why change current practise? Poor at predicting cardiac events50% of first cardiac events are MI.50% events occur in low to mod risk patients>50% patients with MI “average” lipidsFunctional testing inaccurate “So I’m going to live?”Expensive business!Hospital admission / angio $Perfusion scan $1000Cardiologist / stress echo $500Functional 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
3Lipid Management Frequently uncertain who to treat NCEP supports statins in high risk (>20% 10 yr)Moderate risk (10-20% 10yr) group challengingAkosah et al: Young pts mean age 50 presenting MI70% in lower risk category and statin ineligibleEarly plaque detection / lipid lowering therapyWhat 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 accountNCEPSurely 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.
4Coronary Calcification Misguided bias against techniqueProven robust technique in identifying at risk populationCoronary Calcium Score >100 or >75th pecentile identifies a CAD equivalentTechnique 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)
7AHA – 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.
8Original 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):March 27, 2008
9ConclusionThe 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
10Introduction to Coronary CTA Imaging technique accounting for cardiac motion through ECG gatingEarly 1980’s conventional CT1987 EBCT1999 Multi Detector CTAccelerated progression in imaging capability over past decade will continue into forseeable futureDiagnostic capability has at times preceded the critical evaluation of clinical applicationSuccessive generations of CT scanners have been applied to Cardiac imagingThis has resulted in Accelerated….As a result the Diagnostic…..
12TechnologyCardiac motion – Translational, Rotational and Accordian-type movementsSelective coronary angiography gold standardWhole heart covered, real time imagingTemporal resolution of 10msecSpatial resolution 100umButLumen onlyLimited anglesNo cross sectional reconstructionThe 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
13Technology 64 slice CT pivotal technology “Can Do” Spatial resolution 0.35 mm – “isotropic”Slice, dice, any angle, cross sectional analysisTemporal resolution msecDetector array 4 cm wideInfinite Grey scale, image vessel wall, characterise plaque“Can Do”Sensitivity and Specificity ~95% c.f. invasive angiography, ~5% segments unevaluable64 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.
14Helical ScanningHelical scanning involves continuous x-ray exposure and table movement to acquire the most image data in the shortest time.
15Snapshot Pulse is most dose efficient At Z location,waiting for desired heart phaseNO XRAYSZ locationTime
16METHODS - CTA 0.5-0.625 mm slices Single Breath-hold Imaging 80 cc Non-ionic (IODINATED) contrastAggressive B blockade
18Accuracy of Noninvasive CT Angiography: Trial exclusions Technically inadequate scans not included in analysisPatient exclusion criteriaRapid heart ratesIrregular heart beat/arrhythmiasRenal dysfunctionContrast AllergiesBeta-blocker intolerantObesity limits interpretation
19Diagnostic accuracy of CTA AnalysisSensitivity (%)Specificity (%)PPV (%)NPV (%)Stenoses > 50%, per patient93826297Stenoses > 50%, per vessel84915198Stenoses > 70%, per patient49Stenoses > 70%, per vessel85923399ACCURACY study. 232 pts. Chest pain syndromes. Low ppv due to low prevalence of disease in this gp.PPV=positive predictive valueNPV=negative predictive valueMin J. Radiological Society of North America 2007; November 25-30, 2007; Chicago, IL.
21Case 1 - 43 male 43 year old man commenced a new exercise program Left side chest discomfort on exertionCholesterol 6.0, LDL 3.6, HDL 1.3No smoking, diabetes, HT or family history of IHDBMI 26 kg/m2Medications – nilResting ECG – normalWhat next ?CIA Mar 08
22Functional TestObjectively negative stress echocardiogram – 13 minutesHowever, vague left sided chest pain at peak exercise“Is my heart OK ?”CIA Mar 08
24Case 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 presentationNegative Stress Echo after 12 minutes of Bruce protocol. No symptoms with stress testWorrying symptoms and CV risk factors, but negative functional test
25Volume rendered image of Coronary CT Severe LAD and Diagonal branch stenosis
26OutcomeThis 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.
27Case 3 37 yr old pastry chef- referred Aug 05 Sudden death of 40 yr old first cousinBackgroundSVT 3 episodes over last 15 yearsEx smoker 1year (since age 20)FH of IHD father CABG at 63Chol 5.4, LDL 3.4, HDL 1.2, TG 1.9Chol/HDL ratio 4.5Overweight at 100kg (BMI 33)
28Assessment SR 86bpm BP 130/90 ECG ECHO Exercise stress test (echo assisted)11.5 mins of Bruce protocolNormal haemodynamic responseLimited by fatigue no CPNo ECG or ECHO evidence of ischaemia
29Management Lifestyle changes Stay off cigarettes weight loss dietary and exercise adviceFurther investigation ? (asymptomatic)novel risk factors Hs CRP, Lp(a), homocysteineGTTambulatory BP monitor? Sleep studyPharmacological intervention ?
30Cardiovascular Risk Assessment Assessment of 5-10 year risk of coronary eventFramingham risk score (10 year risk)NZ risk calculator ( 5 year risk)Pharmacological intervention if risk>2%/yr or 20%/10yrs
43Left 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
51In the ER?High negative predictive value, therefore CT may help avoid unnecessary hospital admissions, however…Patient preparation24hr scan workup usually not logistically feasibleScanner availabilityCoronary physiology and other investiagations(ECG and biomarkers) well validated for prognosisAll coronary segments may not be visibleApparent non-flow limiting lesion potentially unstable“Triple rule out” –high radiation and contrast dosesHigh volume centre usually provides high quality service