Assessing the Prognostic Value of Coronary Computed Tomography Angiography

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    Journal of the American College of Cardiology Vol. 52, No. 16, 2008 2008 by the American College of Cardiology Foundation ISSN 0735-1097/08/$34.00PubDITORIAL COMMENT

    ssessing the Prognosticalue of Coronary Computedmography Angiography*

    ephan Achenbach, MD, FACC, FESC

    langen, Germany

    mputed tomography (CT) imaging of the coronaryeries is challenging. The coronary vessels are small, andy move very rapidly, so that tremendously high spatiald temporal resolution are necessary to obtain sharpages of the coronary tree. The first CT system success-ly used to visualize the coronary arteries was the electronm tomography (EBT) scanner, which became availablethe late 1980s and early 1990s and was also calledtrafast CT because of its ability to acquire images atprecedented speed. With an exposure time of 100 ms/age, the EBT scanner allowed faster imaging than mostltidetector CT systems in use today, but limitationsluded a spatial resolution much lower than that of currentscanners, rather high image noise, and a long overall

    age acquisition time (patients typically had to hold theirath for more than 30 s).

    See page 1335

    The main application of EBT was the detection andantification of coronary artery calcification. In addition,T first demonstrated the ability of CT imaging to obtainninvasive coronary angiograms after injection of atrast agent. In the mid 1990s, this new developmenteived tremendous interest and fueled the surprisinglyid evolution of CT technology, much of which wasven by the desire to improve the ability of CT to visualizecoronary arteries. Today, 64-slice CT systems, which

    ow rather stable imaging of the coronary vessels, aredely available. Coronary computed tomography angiog-hy (CTA) is considered an appropriate clinical tool inected situations, including ruling out coronary stenoses inptomatic patients with intermediate likelihood of coro-

    itorials published in the Journal of the American College of Cardiology reflect thes of the authors and do not necessarily represent the views of JACC or theerican College of Cardiology.

    lished by Elsevier Inc.som

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    rom the Department of Cardiology, University of Erlangen, Erlangen, Germany.Achenbach receives research grants from Siemens Healthcare and Bayer Scheringrma, and is supported by a grant (01 EV 0708) from Bundesministerium frung und Forschung, Germany.ry artery disease (1). Although numerous comparisons ofimaging to invasive angiography have been published

    d demonstrate a high accuracy for the detection ofstructive coronary artery lesions, very little is knownut the prognostic implications of coronary CTA.The study presented by Ostrom et al. (2) in this issue ofJournal provides data concerning the prognostic value oftrast-enhanced CT visualization of the coronary arteries.e investigators followed up 2,538 patients studied bytrast-enhanced EBT for up to 15 years. Based on theirge number of patients, complete follow-up, and longservation period, they are able to demonstrate that thesence of obstructive and nonobstructive coronary arteryions seen in contrast-enhanced EBT is predictive ofrtality above and beyond traditional risk factors. Dem-stration of lesions is also a better predictor than the mereessment of coronary calcification. The severity of coro-ry lesions and the extent of disease (e.g., 1 affected vesselseveral affected vessels) were associated with mortalityes. After adjustment for risk factors and coronary calciumre, patients with obstructive lesions seen in EBT angiog-hy had an approximately 2-fold risk of death as com-red to patients without detectable atherosclerosis. Inter-ingly, noncalcified, nonstenotic plaque was found to bedictive only if its extent was substantial: only patientso had all 3 vessels affected had an increased mortality.Obviously, the study by Ostrom et al. (2) has someitationsfor example, it is unclear how many patientsre symptomatic and what treatment was initiated basedthe EBT resultsbut it does provide very interestingly data concerning the prognostic implications of coro-ry plaque detected in contrast-enhanced CT imaging. Astypically the case with new and exciting research results,study answers some questions, but also raises many new

    es, some of which are outlined below.mptomatic patients or asymptomatic individuals? Inopinion, it is important to carefully distinguish 2 clinicalnarios. The first scenario is the use of coronary CTA forptomatic patients. For some subgroups of patients whonot have a high likelihood of coronary artery stenoses,s is currently considered appropriate (1). Clinically, theof CT will be ruling out coronary artery stenoses to

    id invasive catheterization. Prognostic studies are neededclarify whether it is safe to replace invasive angiographyCT, and also to determine whether patients in whom CTes out the presence of obstructive lesions (thus avoidingasive angiography) but demonstrates the presence ofnobstructive plaque are at higher risk of cardiac eventsn are patients with entirely normal coronary arteries on. This determination is important in order to make

    propriate recommendations regarding risk modificationsuch patients. The study by Ostrom et al. (2) provides

    doi:10.1016/j.jacc.2008.07.022e data in this respect.The second scenario is that of the asymptomatic patientwhom coronary CTA is performed for the sole purpose

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    JACOctorisk stratification in a primary prevention context. Thisquite a different setting. Most patients in the study bytrom et al. (2) probably had symptoms, and similarly, theother available studies that have investigated prognostic

    plications of coronary CTA were all conducted in pa-nts who were largely symptomatic (37). It is importantt to use results obtained from such patient groups totify coronary CT screening of asymptomatic patients.etest likelihoods and future event risks are substantiallyer, and the balance between test benefit and associatedks (and costs) may be profoundly different from that ofptomatic patients. The use of contrast-enhanced coro-

    ry CTA for risk stratification for asymptomatic patients isrently considered an inappropriate application (1), andmy opinion, the study by Ostrom et al. (2) will notange that.d technology matter? The study by Ostrom et al. (2)s conducted using EBT, which is not widely availableymore. The EBT data collected by Ostrom et al. (2) areremely valuable because they allow a long follow-upriod, but EBT has meanwhile been replaced by multide-tor computed tomography (MDCT), which has highertial resolution and, in general, better image quality thanT. However, this does not mean that detection of plaqueMDCT is easy. Data sets of impeccable quality areuired to assess the presence or absence of nonobstructiveque, and even in expert hands, neither sensitivity norcificity is perfect (8). With adequate image quality,wever, it should be expected that more noncalcifiedque will be identified in MDCT as compared to EBTauble-edged sword. On the one hand, it will make it lessely that a patient with a future event will be missed byDCT. On the other hand, I suspect that even more plaquey be detected by MDCT, and that may lead to a largermber of patients being placed in a high risk category.ain, it is important to keep in mind that only plaque in allessels was predictive of future events in the study by Ostromal. (2). Small, localized plaques have so far not been tied toincreased event risk.ould the mere detection of plaque be enough? Ostromal. (2) used a yes/no model to assess the presence ofstructive and nonobstructive coronary lesions by CT.ost likely, that will not be sufficient in the future (Fig. 1).t all nonobstructive lesions are alikefor example, theyy be small, confined to the vessel wall, and predominantlycified, or they can be large, positively remodelled, andgely noncalcified. However, as noncalcified plaque isserved very frequently by contrast-enhanced coronaryA (more than one-half of all patients in the study bytrom et al. [2], and about 30% of patients in a differentdy [9]), merely evaluating the presence of plaque mayce too many individuals in a high-risk category, withconsequence of (expensive) risk modification treatment

    well as considerable emotional stress. Efforts will have to

    C Vol. 52, No. 16, 2008ber 14, 2008:13446undertaken to identify characteristics that are associatedth increased risk of future events, whether this may bebal features (such as plaque volume), specific aspects of a

    afieaigure 1 Visualization of Proximal and MidLAD by Contrast-Enhanced MDCT in 3 Patients

    isualization of the proximal artery and mid left anterior descending coronaryrtery (LAD) by contrast-enhanced multidetector computed tomography (MDCT) in 3ifferent patients. (A) Visualization of a small calcified plaque (large arrow) alongith some noncalcified plaque (small arrow) in the mid left anterior descendingronary artery. (B) While nominally this patient also demonstrates calcified (largerrow) and noncalcified, nonobstructive plaque (small arrow), the lesion has differ-nt characteristics as compared with A. The noncalcified plaque component isbstantially larger, and the lesion displays pronounced positive remodeling.otentially, this lesion may be more vulnerable than the lesion in A. (C) Not in

    1345AchenbachPrognostic Value of Coronary CTAll cases is image quality high enough to reliably rule in or rule out small noncalci-d plaque. Although coronary stenoses can be ruled out, image noise preventsssessing the presence of noncalcified plaque in this low-dose image.

  • given plaque (such as remodeling), or a combination of both(10). A small, noncalcified plaque may actually be prettyharmless and in fact, the absence of substantial amounts ofnoncalcified plaque may at some point allow downstaging ofpatients concerning their risk, but future research will need toaddress this issue.How much can we afford to spend? Even when leavingthe economic implications of CT angiography for riskstratification completely aside, this test comes at a cost: theinjection of contrast and the associated radiation exposureplace CTA in a completely different category as comparedto, for example, coronary calcium imaging. Low radiationdose protocols are becoming increasingly available for CTA,but flawless image quality is necessary to be able to assess thepresence or absence of plaque with a reasonable degree ofcertainty. Studies performed at very low dose or affected byother sorts of artifacts may be sufficient to rule out thepresence of coronary stenosis, but not necessarily to visualizeorrisuse

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    REFERENCES

    1. Hendel RC, Patel MR, Kramer CM, et al. ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria forcardiac computed tomography and cardiac magnetic resonance imag-ing: a report of the American College of Cardiology FoundationQuality Strategic Directions Committee Appropriateness CriteriaWorking Group, American College of Radiology, Society of Cardio-vascular Computed Tomography, Society for Cardiovascular MagneticResonance, American Society of Nuclear Cardiology, North AmericanSociety for Cardiac Imaging, Society for Cardiovascular Angiographyand Interventions, and Society of Interventional Radiology. J Am CollCardiol 2006;48:147597.

    2. Ostrom MP, Gopal A, Ahmadi N, et al. Mortality incidence and theseverity of coronary atherosclerosis assessed by computed tomographyangiography. J Am Coll Cardiol 2008;52:133543.

    3. Pundziute G, Schuijf JD, Jukema JW, et al. Prognostic value ofmultislice computed tomography coronary angiography in patientswith known or suspected coronary artery disease. J Am Coll Cardiol2007;49:6270

    4. Min JK, Shaw LJ, Devereux RB, et al. Prognostic value of multide-tector coronary computed tomographic angiography for prediction ofall-cause mortality. J Am Coll Cardiol 2007;50:116170.

    5. Gilard M, Le Gal G, Cornily JC, et al. Midterm prognosis of patients

    6.

    7.

    8.

    9.

    10.

    Kecom

    1346 Achenbach JACC Vol. 52, No. 16, 2008Prognostic Value of Coronary CTA October 14, 2008:13446even characterize plaque (Fig. 1). Contrast and radiationks have to be assessed very carefully if ever considering theof CTA in primary prevention settings.

    In summary, the paper by Ostrom et al. (2) is helpful andy welcome as it provides more data on the prognosticplications of coronary visualization using CT techniques.contains the very reassuring message that the absence ofnosis and nonobstructive plaque is associated with a goodgnosis, even in a patient population that was most likelygely symptomatic. However, the results do not justify theof CTA as a screening tool for asymptomatic, primaryvention patients.

    print requests and correspondence: Dr. Stephan Achenbach,partment of Cardiology, University of Erlangen, Ulmenweg 18,langen 91054, Germany. E-mail: stephan.achenbach@uk-ngen.de.with suspected coronary artery disease and normal multislice computedtomographic findings: a prospective management outcome study. ArchIntern Med 2007;167:16869.Lesser JR, Flygenring B, Knickelbine T, et al. Clinical utility ofcoronary CT angiography: coronary stenosis detection and prognosisin ambulatory patients. Catheter Cardiovasc Interv 2007;69:6472.Gaemperli O, Valenta I, Schepis T, et al. Coronary 64-slice CTangiography predicts outcome in patients with known or suspectedcoronary artery disease. Eur Radiol 2008;18:116273.Schroeder S, Achenbach S, Bengel F, et al. Cardiac computedtomography: indications, applications, limitations, and training re-quirements: report of a writing group deployed by the Working GroupNuclear Cardiology and Cardiac CT of the European Society ofCardiology and the European Council of Nuclear Cardiology. EurHeart J 2008;29:53156.Hausleiter J, Meyer T, Hadamitzky M, Kastrati A, Martinoff S,Schmig A. Prevalence of noncalcified coronary plaques by 64-slicecomputed tomography in patients with an intermediate risk forsignificant coronary artery disease. J Am Coll Cardiol 2006;18:3128.Narula J, Finn AV, DeMaria AN. Picking plaques that pop. . . J AmColl Cardiol 2005;45:19703.

    y Words: coronary artery disease y electron beam tomography yputed tomography y prognosis.

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