Temporal trends in utilization of cardiac computed tomography

Journal of Cardiovascular Computed Tomography (2009) 3, 16–21

Original Research Article

Temporal trends in utilization of cardiac computed tomography Ala-Eddin M. Ayyad, MDa, Jason Cole, MDb, Asmir Syed, MDb, Milind Y. Desai, MDa,c, Sandra Halliburton, PhDa,c, Paul Schoenhagen, MDa,c, Scott D. Flamm, MDa,c, Srikanth Sola, MDa,c* a

Cleveland Clinic, Heart and Vascular Institute, Cleveland, OH, USA, bUniversity of South Alabama College of Medicine, Mobile, AL, USA, and cCleveland Clinic, Imaging Institute, Cleveland, OH, USA KEYWORDS: Cardiac CT; Computed tomography

BACKGROUND: Appropriate, inappropriate, and uncertain indications for the use of cardiac computed tomography (CT) were defined by a multisociety document in 2006. We sought to compare the appropriateness of cardiac CT examinations before and after these criteria were published. METHODS: We retrospectively evaluated all patients presenting for cardiac CT examinations in the first 3 months of 2006 and 2007 at a large academic medical center and an unaffiliated large cardiology group private practice. The indication for the examinations were determined from the patients’ medical records. The examinations were then classified as ‘‘appropriate,’’ ‘‘inappropriate,’’ or ‘‘uncertain,’’ based on appropriateness criteria. Examinations that did not fall into any of these categories were classified as ‘‘uncategorized.’’ RESULTS: We evaluated a total of 1409 patients (64.9% men; mean age, 57.6 6 13.4 years). The proportion of appropriate CT examinations increased from 69.5% during the study period in 2006 to 78.5% in 2007 (P 5 0.001). A corresponding decrease was observed in inappropriate CT examinations from 11.5% in 2006 to 4.6% in 2007 (P 5 0.001). No change was observed in the number of CT examinations that were deemed uncertain (12.7% in 2006, and 13.3% in 2007; P 5 NS). CONCLUSION: The number of CT examinations considered appropriate increased during the study period, whereas the number of inappropriate examinations decreased. Cardiologists were more likely than noncardiologists to order examinations that were appropriate during the study period. Ó 2009 Society of Cardiovascular Computed Tomography. All rights reserved.

Introduction Technologic advances and novel clinical applications have led to rapid growth in the use of cardiac computed Conflict of interest: The authors report no conflicts of interest. * Corresponding author. Address correspondence to Srikanth Sola, MD, FACC, FAHA, Department of Cardiology, Sri Sathya Sai Institute of Higher Medical Sciences, EPIP Area, Whitefield, Bangalore, 560 066 India. E-mail address: [email protected] Submitted April 23, 2008. Accepted for publication October 13, 2008.

tomography (CT). Cardiac CT has been shown to be useful in the evaluation of coronary artery anatomy,1–9 the pulmonary veins,10–12 ventricular structure and function,13 the pericardium,14–18 and in patients with valvular19–21 or congenital heart disease.22 In an effort to provide a rational approach to the utilization of noninvasive imaging methods, multiple medical societies collectively developed the Appropriateness Criteria for cardiac CT and cardiac magnetic resonance imaging in 2006.23 According to current literature and

1934-5925/$ -see front matter Ó 2009 Society of Cardiovascular Computed Tomography. All rights reserved. doi:10.1016/j.jcct.2008.10.009

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Temporal trends in use of cardiac CT

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expert opinion, these criteria define appropriate, inappropriate, and uncertain indications for the use of cardiac CT for a wide variety of contemporary clinical indications; however, the level of adherence to these recommendations is unknown. We sought to determine the prevalence of appropriate and inappropriate CT examinations at two highvolume centers with considerable experience in cardiac CT. Because an increasing number of patients are being referred for cardiac CT studies by physicians other than cardiologists, we also evaluated differences in referral patterns between cardiologists and noncardiologists.

CT as well as telephone or direct personal interactions with referring physicians in which the ideal patient population for a cardiac CT examination was explained. When a patient was referred for a cardiac CT examination that was felt to be inappropriate, the referring physician was contacted, and the examination was either cancelled or the reasoning for the test clarified. In particular, screening CTA examinations were discouraged. At the group private practice, cardiac CT examinations were only ordered by cardiologists, and all patients underwent prescreening to ensure that each patient met local health insurance criteria for reimbursement for the examination.

Methods

Statistics

We retrospectively reviewed all cardiac CT examinations that were performed at an academic medical center and an unaffiliated private group cardiology practice (.20 cardiologists) during the first 3 months of 2006 and 2007. Medical records for each patient and the ordering indication for each CT examination were reviewed by two physician investigators with experience in cardiac CT (.3 years). Medical records were available for all patients. Each examination was classified by consensus as appropriate, inappropriate, or uncertain based on the appropriateness criteria. Patients without known coronary artery disease who were referred for a coronary CT angiography (CTA) were classified as low, intermediate, or high risk of coronary artery disease (CAD), based on their clinical risk factors at the time of presentation.24,25 Studies for which the indication could not be classified into any appropriateness criteria category were classified as uncategorized. For coronary CTA examinations, we also evaluated the relation between the type of ordering physician (cardiologist or noncardiologist) and CTA examination results. A noncardiologist was defined as any physician with a specialty other than cardiology (ie, internal medicine, family practice, cardiac surgery, etc). Each CTA examination was classified as clinically significant if .50% luminal stenosis was present in at least one coronary artery, a coronary artery bypass graft (CABG) was found to be occluded (previously not known to be occluded), or a clinically important coronary artery anomaly was present. Because the cardiac CT laboratory at the academic medical center also performs a large number of CT examinations for evaluation of the aorta (.6000/year), we excluded these examinations from analysis because most of these would be considered appropriate and would bias the study results.

Data are presented as the mean 6 SD for continuous variables and as the percentage of total patients for categorical variables. The independent sample t test and the chi-square or Mann-Whitney test were used for comparison of continuous and categorical variables, as appropriate. A P value of , 0.05 was considered statistically significant, and all P values were 2 sided. Calculations were performed with SAS software (version 15.0; SAS Institute, Cary, NC).

Patient screening Coinciding with the publication of the appropriateness criteria in October 2006, a formal and continuous effort was made at the academic medical center to educate referring physicians about the appropriate use of cardiac CT. This consisted of monthly educational conferences on cardiac

Results A total of 1409 patients underwent cardiac CT examinations during the study period (64.9% men; mean age 57.6 6 13.4 years). Of these, 763 examinations were performed during the first 3 months of 2006 and 646 in the same period of 2007 (P , 0.001). There was a higher proportion of patients with coronary artery disease and diabetes in 2007 compared with 2006 (Table 1). The proportion of cardiac CT examinations that were considered appropriate increased during the study period, from 69.8% (530/763) in 2006 to 78.5% (507/646) in 2007 (P 5 0.001). A corresponding decrease was observed in the proportion of examinations deemed inappropriate from 11.4% (88/763) in 2006 to 4.6% (30/646) in 2007; P 5 0.001). No significant difference was observed in the number of examinations that were considered uncertain (12.7% [97/ 763] in 2006; 13.3% [86/646] in 2006; P 5 NS). A small number of examinations did not fit into any of the appropriateness criteria categories and were considered uncategorized (6.1% [48/763] in 2006 vs. 3.6% [23/646] in 2007; P 5 0.03). The most common indication for coronary CTA was the evaluation of the coronary arteries in both 2006 (41%) and 2007 (37.3%); P 5 NS; Table 2. Other common indications included evaluation of pulmonary venous anatomy before or after radiofrequency ablation for atrial fibrillation and preoperative evaluation of the relation of the cardiovascular structures to the sternum before redo-sternotomy (Table 3). All of the cardiac CT examinations classified as inappropriate in our study were ordered for evaluation of the

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Table 1

Characteristics of the study population

Characteristic

2006 (n 5 763)

2007 (n 5 646)

P value

Age (y), mean 6 SD Male, % (n) White, % (n) Hypertension, % (n) Diabetes, % (n) Hyperlipidemia, % (n) Smoking, % (n) Coronary artery disease, % (n) Heart failure, % (n) Peripheral arterial disease, % (n) Stroke, % (n)

57.2 64.7 87 47.4 12.6 54.3 37.9 22.2 10.3 6.8 5.5

58.11 6 13.3 65.2 (421) 85.9 (555) 52.3 (338) 17 (110) 53.3 (344) 39.5 (255) 28.2 (182) 12.7 (82) 7.3 (47) 4.6 (30)

0.60 0.84 0.43 0.053 0.034 0.92 0.11 0.005 0.12 0.62 0.79

6 13.6 (494) (664) (362) (96) (414) (289) (169) (79) (52) (42)

Patients were studied during the first 3 months of 2006 and 2007.

coronary arteries. The majority of these (76%) were coronary CTA examinations done for screening of asymptomatic patients with low-to-moderate risk of CAD, which were typically ordered as part of comprehensive health evaluations at the academic medical center. The number of screening coronary CT angiograms decreased from 6.9% in 2006 to 3.1% in 2007 (P 5 0.01). None of the inappropriate examinations in our study were ordered at the private group practice, where prescreening and insurance authorization were required before each CT examination. Inappropriate cardiac CT examinations were more frequently ordered by noncardiologists than by cardiologists during the study period (Table 4). Both groups, however, showed a decrease in the number of examinations that were considered inappropriate, with a corresponding increase in appropriate examinations during the study period. Coronary CTA examinations classified as

Table 2

appropriate had a higher incidence of clinically significant findings, compared with those examinations that were classified as inappropriate (46.1% compared with 24.5%; P 5 0.0021). The most common indication for examinations classified as uncertain included coronary CTA for evaluation of symptomatic CAD in patients with an intermediate pretest probability of CAD who were able to exercise and had an interpretable electrocardiogram (144/1409; 10.2%). Other CT examinations classified as uncertain included evaluation of native and prosthetic cardiac valves in patients with limited echocardiograms (17/1409; 1.2%) and evaluation of bypass graft patency in patients with chest pain and prior CABG (17/1409; 1.2%). The most common indications for examinations that were not included in the appropriateness criteria and were considered uncategorized included evaluation for arrhythmogenic right ventricular dysplasia (27 of

Cardiac CT exams by clinical indication

Indication

2006 (n 5 763)

2007 (n 5 646)

P value

Appropriateness category/ indication23

Coronary artery anatomy (coronary CTA), % (n) Pulmonary vein anatomy for pulmonary vein isolation for atrial fibrillation, % (n) Evaluation of bypass graft location/relation of cardiovascular structures to sternum before redo sternotomy, % (n) Pericardial disease, % (n) Congenital heart disease, % (n) Cardiac mass or tumor, % (n) Noninvasive coronary vein mapping before placement of biventricular pacemaker, % (n) Bypass graft patency in patients with chest pain and prior CABG, % (n) Characterization of native and prosthetic cardiac valves, % (n) Arrhythmogenic right ventricular dysplasia, % (n) Other, % (n)

41 (313) 37.1 (283)

37.3 (241) 36.7 (237)

— 0.81

See Table 3 Appropriate, 35

4.6 (35)

14.2 (92)

,0.0001

Appropriate, 37

2.5 2.3 1.2 0.8

(18) (17) (9) (6)

2.3 1.5 2 0.6

(8) (10) (13) (4)

0.99 0.052 0.29 0.24

Appropriate, Appropriate, Appropriate, Appropriate,

34 28 33 36

4.5 (14)

1.2 (3)

0.029

Uncertain, 23

0.9 (7)

1.5 (10)

0.28

Uncertain, 32

2.6 (20) 7.2 (55)

1.1 (7) 2.2 (14)

0.04 0.03

Uncategorized Uncategorized

Ayyad et al Table 3

Temporal trends in use of cardiac CT

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Coronary CTA to evaluate coronary arteries or bypass grafts, by clinical indication and appropriateness category (23)

Clinical indication

2006 (n 5 313)

2007 (n 5 241)

P value

Appropriateness category/ indication23

Chest pain, nondiagnostic stress test, % (n) Evaluation of suspected coronary anomalies, % (n) Screen for CAD in low to intermediate risk patient (Framingham criteria), % (n) Chest pain, intermediate pre-test probability, ECG interpretable and able to exercise, % (n) Other (evaluate coronary arteries prior to valvular heart surgery; evaluate transplant vasculopathy; etc), % (n)

32.3 (101)

38.2 (92)

0.115

Appropriate, 16

0.43

Appropriate, 4

5.8 (18)

5 (12)

16.9 (53)

8.3 (20)

0.0001

Inappropriate, 10, 11

21.4 (67)

40 (77)

0.29

Uncertain, 1

19.2 (60)

19.1 (46)

—

Variable

70 uncategorized examinations) in patients with contraindications to magnetic resonance imaging, evaluation of coronary artery anatomy in patients undergoing valvular heart surgery (17 of 70), and evaluation of transplant vasculopathy in heart transplant recipients (6 of 70).

Discussion This study represents one of the first attempts to apply the appropriateness criteria for cardiac CT to currently clinical practice. We found that referrals for CT examinations considered appropriate increased from 69.5% during the study period in 2006 to 78.5% in 2007 (absolute increase of 9%), whereas the number of CT examinations considered inappropriate decreased from 11.5% to 4.6% in 2007 during the study period (6.9% decrease). These findings likely reflect a greater awareness of the role and limitations of cardiac CT among physicians who order and interpret these examinations, as well as changes in reimbursement policies for cardiac CT. Both factors are probably related to the growing clinical experience as reflected in the published appropriateness criteria for cardiac CT. Our study highlights the role that prescreening and reimbursement practices can play in reducing cardiac CT

Table 4

examinations that may be considered inappropriate. At the academic medical center, medical contraindications (patient age or likelihood of calcified coronary arteries or both, renal function, cardiac rhythm, etc) were the primary means used to exclude a patient from a cardiac CT examination during the study period. All of the inappropriate CT examinations in our study were performed at this center and largely consisted of self-pay screening coronary CTA examinations performed as part of a comprehensive health evaluation. Such examinations were subsequently discouraged, coinciding with the publication of the appropriateness criteria. In contrast, all referrals for cardiac CT examinations performed at the private group practice were prescreened not only for medical contraindications but also to ensure that they met local insurance criteria for reimbursement. Despite these differences in practice patterns, the most examinations during the second review period in our study could be classified as appropriate. Cardiologists were more likely than noncardiologists in our study to order cardiac CT examinations that were considered appropriate. This probably reflects the greater familiarity with the role and limitations of cardiac CT among cardiologists than among noncardiologists. As the use of cardiac CT expands over the next few years, there will be an increased need for medical societies and interpreting physicians to educate referring physicians

Cardiac CT to evaluate coronary arteries or bypass grafts, by ordering physician Ordering physician

Indication

Cardiologist (n 5 436)

Noncardiologist (n 5 118)

P value

Appropriate, % (n) Inappropriate, % (n) Uncertain, % (n)

58.5 (255) 13.3 (58) 28.2 (123)

29.7 (35) 43.2 (51) 27.1 (32)

,0.0001 ,0.0001 0.8

CT examinations considered appropriate were more frequently ordered by cardiologists, whereas inappropriate examinations more frequently ordered by noncardiologists during the study period.

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about which patients are most suited for evaluation by this imaging method. A number of CT examinations in our study had indications that were considered uncertain or uncategorized by the appropriateness criteria. Those indications included evaluation of native and prosthetic cardiac valves (typically in patients with complex valve disease or limited echocardiograms or both), bypass graft patency, and transplant vasculopathy in heart transplant recipients, areas of active research in cardiac CT.26–33 It is expected that some of these designations of appropriateness will change over time as additional data about the role of CT become available. Our study has several limitations that must be noted. First, our study was conducted at two busy cardiac CT centers with a combined volume of .14,000 CT examinations per year. We chose two different centers with different patient populations (northeast Ohio and south Alabama) and different physician referral patterns (.1000 physicians, including 90 cardiologists at Cleveland Clinic; .20 cardiologists at the group practice) in an attempt to capture different cardiac CT practices. Nevertheless, the results of our study may not be representative of all centers performing cardiac CT. Furthermore, some of the indications for cardiac CT examinations (pulmonary vein anatomy before or after ablation for atrial fibrillation, cardiac masses, etc) performed at Cleveland Clinic may not be common at smaller centers with a more limited patient population. These less-common indications are also less likely to be used inappropriately compared with coronary CTA, whereby the potential for abuse or inappropriate use is much higher. Second, this was an observational study, and it is not possible to separate the direct influence of the appropriateness criteria from other factors that may have affected physician referrals for cardiac CT, such as changes in insurance reimbursement policies and increasing familiarity among physicians of the role of this imaging method in patient care. Finally, incomplete documentation, a limitation of many quality of care studies, may have led to some studies being incorrectly classified as inappropriate. Nevertheless, we feel that the results of our study suggest a trend toward more appropriate utilization of cardiac CT, in accordance with the published criteria. Cardiac CT continues to expand at a rapid pace, fueled in part by rapid technologic advances, publication of validation and outcomes studies, and the attractiveness of being able to gain important clinical information noninvasively. Nevertheless, the economic effect of uncontrolled utilization for clinically inappropriate indications as well as unwarranted downstream testing and treatment is an important concern for both government and private payers. The results of our study, however, show that there has been a significant increase in the number of CT examinations that are considered appropriate during the study period, with a corresponding decrease in the number of inappropriate examinations.

References 1. Nieman K, Cademartiri F, Lemos PA, Raaijmakers R, Pattynama PM: de Feyter PJ: Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation. 2002;106(16):2051–4. 2. Kuettner A, Kopp AF, Schroeder S, Rieger T, Brunn J, Meisner C, Heuschmid M, Trabold T, Burgstahler C, Martensen J, Schoebel W, Selbmann HK, Claussen CD: Diagnostic accuracy of multidetector computed tomography coronary angiography in patients with angiographically proven coronary artery disease. J Am Coll Cardiol. 2004;43(5):831–9. 3. Martuscelli E, Romagnoli A, D’Eliseo A, Razzini C, Tomassini M, Sperandio M, Simonetti G, Romeo F: Accuracy of thin-slice computed tomography in the detection of coronary stenoses. Eur Heart J. 2004; 25(12):1043–8. 4. Raff GL, Gallagher MJ, O’Neill WW, Goldstein JA: Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol. 2005;46(3):552–7. 5. Garcia MJ, Lessick J, Hoffmann Mh: CATSCAN Study I: Accuracy of 16-row multidetector computed tomography for the assessment of coronary artery stenosis. JAMA. 2006;296(4):403–11. 6. Leber AW, Becker A, Knez A, von Ziegler F, Sirol M, Nikolaou K, Ohnesorge B, Fayad ZA, Becker CR, Reiser M, Steinbeck G, Boekstegers P: Accuracy of 64-slice computed tomography to classify and quantify plaque volumes in the proximal coronary system: a comparative study using intravascular ultrasound. J Am Coll Cardiol. 2006;47(3):672–7. 7. Leber AW, Knez A, von Ziegler F, Becker A, Nikolaou K, Paul S, Wintersperger B, Reiser M, Becker CR, Steinbeck G, Boekstegers P: Quantification of obstructive and nonobstructive coronary lesions by 64-slice computed tomography: a comparative study with quantitative coronary angiography and intravascular ultrasound. J Am Coll Cardiol. 2005;46(1):147–54. 8. Mollet NR, Cademartiri F, van Mieghem CA, Runza G, McFadden EP, Baks T, Serruys PW, Krestin GP: de Feyter PJ: High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation. 2005; 112(15):2318–23. 9. Ropers D, Rixe J, Anders K, Kuttner A, Baum U, Bautz W, Daniel WG, Achenbach S: Usefulness of multidetector row spiral computed tomography with 64- x 0.6-mm collimation and 330-ms rotation for the noninvasive detection of significant coronary artery stenoses. Am J Cardiol. 2006;97(3):343–8. 10. Schwartzman D, Lacomis J, Wigginton WG: Characterization of left atrium and distal pulmonary vein morphology using multidimensional computed tomography. J Am Coll Cardiol. 2003;41(8):1349–57. 11. Stanford W, Breen JF: CT evaluation of left atrial pulmonary venous anatomy. Int J Cardiovasc Imaging. 2005;21(1):133–9. 12. Choi SI, Seo JB, Choi SH, Lee SH, Do KH, Ko SM, Lee JS, Song JW, Song KS, Choi KJ, Kim YH, Lim TH: Variation of the size of pulmonary venous ostia during the cardiac cycle: optimal reconstruction window at ECG-gated multi-detector row CT. Eur Radiol. 2005; 15(7):1441–5. 13. Schlosser T, Pagonidis K, Herborn CU, Hunold P, Waltering KU, Lauenstein TC, Barkhausen J: Assessment of left ventricular parameters using 16-MDCT and new software for endocardial and epicardial border delineation. AJR Am J Roentgenol. 2005;184(3):765–73. 14. Wang ZJ, Reddy GP, Gotway MB, Yeh BM, Hetts SW, Higgins CB: CT and MR imaging of pericardial disease. Radiographics. 2003; 23(Spec No):S167–80. 15. Boxt LM, Lipton MJ, Kwong RY, Rybicki F, Clouse ME: Computed tomography for assessment of cardiac chambers, valves, myocardium and pericardium. Cardiol Clin. 2003;21(4):561–85. 16. Axel L: Assessment of pericardial disease by magnetic resonance and computed tomography. J Magn Reson Imaging. 2004;19(6):816–26.

Ayyad et al

Temporal trends in use of cardiac CT

17. Rienmuller R, Groll R, Lipton MJ: CT and MR imaging of pericardial disease. Radiol Clin North Am. 2004;42(3):587–601. 18. Oyama N, Oyama N, Komuro K, Nambu T, Manning WJ, Miyasaka K: Computed tomography and magnetic resonance imaging of the pericardium: anatomy and pathology. Magn Reson Med Sci. 2004;3(3):145–52. 19. Alkadhi H, Bettex D, Wildermuth S, Baumert B, Plass A, Grunenfelder J, Desbiolles L, Marincek B, Boehm T: Dynamic cine imaging of the mitral valve with 16-MDCT: a feasibility study. AJR Am J Roentgenol. 2005;185(3):636–46. 20. Alkadhi H, Wildermuth S, Plass A, Bettex D, Baumert B, Leschka S, Desbiolles LM, Marincek B, Boehm T: Aortic stenosis: comparative evaluation of 16-detector row CT and echocardiography. Radiology. 2006;240(1):47–55. 21. Coche E, Mauel E, Beauloye C, Pasquet A: Tricuspid valve endocarditis and septic pulmonary emboli illustrated by ECG-gated multislice CT of the chest. Eur Heart J. 2006;27(1):20. 22. Ley S, Zaporozhan J, Arnold R, Eichhorn J, Schenk JP, Ulmer H, Kreitner KF, Kauczor HU: Preoperative assessment and follow-up of congenital abnormalities of the pulmonary arteries using CT and MRI. Eur Radiol. 2007;17(1):151–62. 23. Hendel RC, Patel MR, Kramer CM, Poon M, Hendel RC, Carr JC, Gerstad NA, Gillam LD, Hodgson J,Kim RJ, Kramer CM, Lesser JR, Martin ET, Messer JV, Redberg RF, Rubin GD, Rumsfeld JS, Taylor AJ, Weigold WG, Woodard PK, Brindis RG, Hendel RC, Douglas PS, Peterson ED, Wolk MJ, Allen JM, Patel MR: ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography and cardiac magnetic resonance imaging: a report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American College of Radiology, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, American Society of Nuclear Cardiology, North American Society for Cardiac Imaging, Society for Cardiovascular Angiography and Interventions, and Society of Interventional Radiology. J Am Coll Cardiol. 2006;48(7):1475–97. 24. Gibbons RJ, Balady GJ, Bricker JT, Chaitman BR, Fletcher GF, Froelicher VF, Marck DB, McCallister BD, Mooss AN, O’Reilly MG, Winters WL, Gibbons RJ, Antman EM, Alpert JS, Faxon DP, Fuster V, Gregoratos G, Hiratzka LF, Jacobs AK, Russell RO, Smith SC: American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Committee to Update the 1997 Exercise Testing Guidelines: ACC/AHA 2002 guideline update for exercise testing: Summary article. A report of the

21

25.

26.

27.

28.

29.

30.

31.

32.

33.

American College of Cardiology/American Heart Association Task force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). J Am Coll Cardiol. 2002;40:1531–40. Grundy SM, Pasternak R, Greenland P, Smith S Jr., Fuster V: ACC/AHA scientific statement: assessment of cardiovascular risk by use of multiple-risk-factor assessment equations: a statement for healthcare professionals from the American Heart Association and the American College of Cardiology. J Am Coll Cardiol. 1999;34: 1348–59. Meyer TS, Martinoff S, Hadamitzky M, Will A, Kastrati A, Schomig A, Hausleiter J: Improved noninvasive assessment of coronary artery bypass grafts with 64-slice computed tomographic angiography in an unselected patient population. J Am Coll Cardiol. 2007;49: 946–50. Ropers D, Pohle FK, Kuettner A, Pflederer T, Anders K, Daniel WG, Bautz W, Baum U, Achenbach S: Diagnostic accuracy of noninvasive coronary angiography in patients after bypass surgery using 64-slice spiral computed tomography with 330-ms gantry rotation. Circulation. 2006;114(22):2334–41. Meijboom WB, Mollet NR, Van Mieghem CA, Kluin J, Weustink AC, Pugliese F, Vourvouri E, Cademartiri F, Bogers AJ, Krestin GP: de Feyter PJ: Pre-operative computed tomography coronary angiography to detect significant coronary artery disease in patients referred for cardiac valve surgery. J Am Coll Cardiol. 2006;48(8):1658–65. Romeo G, Houyel L, Angel CY, Brenot P, Riou JY, Paul JF: Coronary stenosis detection by 16-slice computed tomography in heart transplant patients: comparison with conventional angiography and impact on clinical management. J Am Coll Cardiol. 2005;45(11):1826–33. Schlosser T, Konorza T, Hunold P, Kuhl H, Schmermund A, Barkhausen J: Noninvasive visualization of coronary artery bypass grafts using 16-detector row computed tomography. J Am Coll Cardiol. 2004;44(6):1224–9. Feuchtner GM, Muller S, Bonatti J, Schachner T, Velik-Salchner C, Pachinger O, Dichtl W: Sixty-four slice CT evaluation of aortic stenosis using planimetry of the aortic valve area. Am J Roentgenol. 2007; 189(1):197–203. Pannu HK, Jacobs JE, Lai S, Fishman EK: Gated cardiac imaging of the aortic valve on 64-slice multidetector row computed tomography: preliminary observations. J Computer Assisted Tomog. 2006;30(3): 443–6. Sigurdsson G, Carrascosa P, Yamani MH, Greenberg NL, Perrone S, Lev G, Desai MY, Garcia MJ: Detection of transplant coronary artery disease using multidetector computed tomography with adaptive multisegment reconstruction. J Am Coll Cardiol. 2006;48(4):772–8.