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Journal of the American College of Cardiology Vol. 44, No. 6, 2004© 2004 by the American College of Cardiology Foundation ISSN 0735-1097/04/$30.00Published by Elsevier Inc. doi:10.1016/j.jacc.2004.06.044

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DITORIAL COMMENT

oninvasive Multi-Sliceomputed Tomographyoronary Angiographyn Emerging Clinical Modality*

. J. de Feyter, MD, FACC, K. Nieman, MDotterdam, The Netherlands

-ray angiography with selective contrast injection throughardiac catheterization remains the reference standard forhe evaluation of the coronary arteries, but noninvasivelternatives, such as magnetic resonance imaging or com-uted tomography (CT), have been developed, the latter ofhich seems most robust for the detection of coronary

tenosis at this moment.Earlier reports using 4-detector row multi-slice computed

omography (MSCT) were promising, but the sensitivitynd specificity to detect significant coronary stenosis, vary-ng from 75% to 95% and from 84% to 98%, respectively,ere achieved after the exclusion of coronary segments with

nadequate image quality (1–5). Between 6% and 32% of theoronary segments were regarded as not interpretable as aesult of cardiac or respiratory motion artifacts or severealcifications and high heart rates.

See pages 1224 and 1230

The current-generation 16-detector row CT scannersith a rotation time of 420 ms, in combination with heart

ate control by beta-receptor blockers, seem to offer aramatic improvement in image quality, quality consistency,nd consequently diagnostic performance without exclusionf segments because of suboptimal image quality.Ropers et al. (6) reported a sensitivity of 92% and a

pecificity of 93% but excluded 12% of the coronary seg-ents because of inadequate image quality. Nieman et al.

7) demonstrated a sensitivity of 95% and a specificity of6% by 16-slice MSCT in comparison with conventionalngiography to detect significantly stenosed coronary arter-es. In this report, none of the coronary segments werexcluded from analysis.

In this issue of the Journal, Kuettner et al. (8) evaluatedhe diagnostic performance of 16-detector row MSCT inomparison with conventional angiography in a populationf 58 symptomatic patients. Two patients were excludedrom analysis. They also included patients who had under-one coronary artery bypass surgery, which made the inter-

*Editorials published in the Journal of the American College of Cardiology reflect theiews of the authors and do not necessarily represent the views of JACC of themerican College of Cardiology.

pFrom the Erasmus Medical Center, Rotterdam, The Netherlands.

retation of the diagnostic performance of MSCT for theoronary arteries problematic. Much to their credit, they didot exclude any coronary segments from analysis based onhe image quality. They reported a sensitivity of 72% and apecificity of 97% to detect significant stenoses, with con-entional angiography as the standard of reference. Thesegures, which deviate from the earlier studies, could be theesult of a different patient population (i.e., patients whonderwent coronary artery bypass grafting, patients with aower disease prevalence in terms of stenoses or calcium,atients who were older (�70 years of age), or patients whoeceived less intensive beta-receptor blocking). Alterna-ively, these figures could be the result of a more exclusion-riven, rather than detection-driven evaluation and, there-ore, merely represent another position on the sameeceiver-operator curve. They do confirm the observer-ependence of the visual and semiquantitative interpretationf CT angiograms and underline the urgent need forbjective and accurate quantification tools.Severe calcification remains to be a significant problem

or the interpretation of CT angiograms and the detectionf coronary stenosis. Kuettner et al. (8) stratified the resultsccording to the coronary calcium score from a scan withoutontrast enhancement, which was acquired prior to theontrast-enhanced angiographic acquisition. As expected,he diagnostic performance was poor in patients with morextensive coronary calcification. In patients with limitedoronary calcium (Agatston score �1,000) a sensitivity andpecificity of 98% and 98% was achieved, compared with8% and 87% in patients with a higher calcium scoreAgatston score �1,000).

SCT ASSESSMENT OF CORONARY BYPASS GRAFTS

ecause of their larger diameter size and lesser mobility,oronary bypass grafts are more accessible to noninvasivevaluation. Evaluation of proximal graft patency has beenemonstrated with electron-beam CT and spiral CT,hereas the evaluation of distal graft patency, disease at the

nsertion site, or nonocclusive graft stenoses have remainedhallenging (9–16).

In this issue of the Journal, Schlosser et al. (17) report onhe noninvasive visualization of coronary artery bypass graftssing 16-detector row MSCT. They included 54 patients, 3f whom were excluded because of irregular heart rhythm orast heart rate despite beta-blockade. A total of 131 bypassrafts (40 internal mammary artery and 91 venous grafts)ere available for evaluation.All arterial graft conduits were accessible, although 26%

f the distal anastomoses to the left anterior descendingoronary artery and diagonal branch could not be evaluateds the result of poor opacification or artifacts caused byetal clips. Only four arterial grafts showed occlusive

esions, of which three were correctly detected, whereas all

atent arterial grafts were correctly classified. All venous

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1239JACC Vol. 44, No. 6, 2004 de Feyter and NiemanSeptember 15, 2004:1238–40 Editorial Comment

ypass grafts and proximal anastomoses were evaluable,lthough 26% of the distal anastomoses could not bevaluated. With respect to the patency of the evaluableenous grafts, the assessment by MSCT was entirely cor-ect. Multi-slice computed tomography detected six nonoc-lusive stenoses, of which only a single case could beonfirmed by conventional angiography. The sensitivity andpecificity were 96% and 95%, respectively, after the exclu-ion of non-evaluable anastomoses. These results, as well ashe case examples, illustrate the high image quality of

SCT, which allows the detailed evaluation of bypassrafts. However, to become a truly clinically useful tool inymptomatic patients after coronary artery bypass grafting,oninvasive imaging modalities should be able to evaluatehe native vasculature, in addition to the bypass grafts,ecause disease progression in the coronary arteries could beesponsible for reoccurrence of anginal symptoms as well16). These patients often present after bypass with diffuseoronary artery disease and advanced calcification and areherefore more difficult to assess as may have been suggestedy the results in the study by Kuettner et al. (8).

HAT MAY WE EXPECT OF MSCTORONARY ANGIOGRAPHY IN THE FUTURE?

irst and foremost, MSCT technology must advance tovercome its most significant limitation, which is its sus-eptibility to residual motion artifacts, particularly in pa-ients with a higher heart rate. Overcoming this limitationequires further acceleration of the X-tube rotation or othereans to significantly improve the temporal resolution of

he system. The current technology performs sufficiently inatients with a heart rate �70 min�1. Multi-segmentaleconstruction algorithms, which combine isocardiophasicata from consecutive heart cycles to reconstruct each slicend improve the effective temporal resolution, or beta-eceptor blockers for heart rate deceleration, will be requiredor interpretable image quality in those patients with a heartate that exceeds 70 min�1.

Although electron-beam CT lacks the spatial resolutionnd the number of detector rows of MSCT, it does provideata acquisition with a temporal resolution of 100 ms and

ess with the most recently introduced generation scanners.o what extent the respective advantages of either CT

echnology compensate for the disadvantages needs to beetermined in comparative trials.Luminal assessment in the presence of highly attenuatingaterial such as calcium or stents seems somewhat im-

roved with 16-detector MSCT but would further benefitrom an increased spatial resolution and dedicated imageeconstruction algorithms. Atrial fibrillation or other per-istent arrhythmia that result in inconsistent end-diastolicentricular volumes and consequently varying positions ofhe coronary arteries are not suited for the current CT

echnology, which requires a number of consecutive heart

ycles of approximately equal length to build up a completeoronary angiogram.

The considerable radiation exposure of MSCT (8 to 13Sv) and, to a lesser extent of electron-beam CT (1.5 to 2.0Sv), remains a matter of concern (18,19). Efforts by theanufacturers to reduce the exposure without compromise

o the image quality are desired to accept CT coronaryngiography as a truly less-harmful investigative tool.

HAT WILL BE THE PLACE OFSCT IN CARDIOLOGY PRACTICE?

e cannot and should not expect MSCT or other nonin-asive modalities to equal the high quality and diagnosticersatility of conventional catheter-based coronary angiog-aphy. Instead, we need to determine when and how thedvantages of these techniques (i.e., fast, relatively inexpen-ive, patient-friendly, and relatively harmless) should bexploited to benefit the management of patients withpossible) coronary artery disease. Whether MSCT is usefuls a screening method in a selected patient population, as anlternative to exercise testing, myocardial perfusion, orobutamine stress testing, or as an alternative to conven-ional angiography in patients with favorable characteristicsi.e., a regular heart rhythm with low heart rate and an loworonary calcium load, or in various other patient groupsith differences in prevalence and clinical presentationarying from asymptomatic to stable, unstable angina, orcute myocardial infarction) needs to be evaluated in futurerials.

The technological progress of MSCT coronary imaginguring the past few years has been impressive, and we feelonfident that continuing technical innovations will over-ome many of the current limitations to advance clinicalmplementation of noninvasive coronary imaging. Theuestion is not whether it is possible to replace diagnosticnvasive coronary angiography but rather when; however, it

ay require several years to fully comprehend the role ofSCT in various clinical situations.

eprint requests and correspondence: Dr. P. J. de Feyter, Erasmusedical Center, Thoraxcenter, Room Bd 410, Dr. Molewater-

lein 40, 3015 GD Rotterdam, The Netherlands. E-mail:.j.defeyter@erasmusmc.nl.

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