Ruling Out Coronary Artery Disease with Noninvasive Coronary ...

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ORIGINAL RESEARCH

Ruling Out Coronary Artery Disease with Noninvasive Coronary Multidetector CT Angiography before Noncoronary Cardiovascular Surgery1 Paz Catalán, MD Rubén Leta, MD Alberto Hidalgo, MD José Montiel, MD Xavier Alomar, MD David Viladés, MD Antonio Barros, MD Sandra Pujadas, MD Francesc Carreras, MD, FESC Josep M. Padró, MD Juan Cinca, MD, FESC Guillem Pons-Lladó, MD

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From the Cardiac Imaging Unit (P.C., R.L., A.H., X.A., A.B., S.P., F.C., G.P.L.), Departments of Cardiovascular Surgery (J.M., J.M.P.) and Cardiology (D.V., J.C.), Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, Clínica Creu Blanca, Reina Elisenda de Montcada 17, Barcelona 08034, Spain. Received February 27, 2010; revision requested April 30; revision received July 21; accepted August 19; final version accepted August 31. P.C. supported in part by a research grant from Toshiba Medical Systems–Spain. Address correspondence to P.C. (e-mail: [email protected] ). q

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Purpose:

To assess the usefulness of preoperative coronary computed tomographic (CT) angiography in the detection of coronary artery disease (CAD) in nonselected patients scheduled to undergo noncoronary cardiovascular surgery to avoid unnecessary invasive coronary angiography (ICA).

Materials and Methods:

The institutional review board approved the study protocol; informed consent was given. This prospective study involved 161 consecutive patients who underwent coronary calcium scoring and coronary CT angiography before undergoing noncoronary cardiovascular surgery. Seven patients were excluded because of contraindications to CT angiography. The major indication of noncoronary cardiovascular surgery was valvular heart disease (121 patients). Follow-up was performed at a median of 20 months to define ischemic events described as acute coronary syndrome or death secondary to acute coronary syndrome, arrhythmias, or cardiac failure. Multivariate analysis was performed to determine predictors of nondiagnostic coronary CT angiography. Kaplan-Meier analysis was performed to evaluate outcome at follow-up.

Results:

Twenty-one patients did not undergo surgery, which left 133 patients as the study group. Atrial fibrillation was present in 45 of 133 patients. The interquartile range of the Agatston coronary calcium score was 0–471. Coronary CT angiography was diagnostic in 108 of 133 patients. Of these, 93 of 108 had no significant CAD (ⱕ50% stenosis), and noncoronary cardiovascular surgery was performed in them without preoperative ICA. No patients in this group had postoperative ischemic events at follow-up. Coronary CT angiography was nondiagnostic in 25 of 133 patients who were referred for preoperative ICA. Multivariate analysis showed Agatston score to be the only independent predictor of nondiagnostic coronary CT angiography (odds ratio = 1.002; 95% confidence interval: 1.001, 1.003; P = .001). The best Agatston score cutoff for diagnostic coronary CT angiography was 579.

Conclusion:

In nonselected patients scheduled to undergo noncoronary cardiovascular surgery, preoperative coronary CT angiography was diagnostic in 81% of cases. Preoperative ICA could be safely avoided in patients without significant CAD by using coronary CT angiography. The Agatston score, but not the presence of atrial fibrillation, was an independent predictor of nondiagnostic coronary CT angiography. q

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Supplemental material: http://radiology.rsna.org/lookup /suppl/doi:10.1148/radiol.10100384/-/DC1

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Radiology: Volume 258: Number 2—February 2011

CARDIAC IMAGING: Coronary CT Angiography to Depict Coronary Artery Disease

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reoperative evaluation of patients scheduled to undergo noncoronary cardiovascular surgery includes the use of invasive coronary angiography (ICA) to rule out the coexistence of significant coronary artery disease (CAD) (1,2). Despite the absence of apparent clinical symptoms of angina, prevalence of significant CAD in this population has been reported to be between 8% and 41% (3,4). The relevance of this finding lies in the observation that revascularization in these patients in addition to the procedure of noncoronary cardiovascular surgery reduces the occurrence of peri- and postoperative adverse major clinical events (5). Multidetector coronary computed tomographic (CT) angiography of the coronary arteries is nowadays a reliable technique to rule out significant CAD, with a proved high negative predictive value, particularly in patients with low or intermediate pretest probability of

Advances in Knowledge n In patients scheduled to undergo noncoronary cardiovascular surgery, coronary CT angiograms are of diagnostic image quality in 81% of cases. n The presence of atrial fibrillation is not a limitation for performing diagnostic coronary CT angiography, provided that the ventricular heart rate is adequately controlled to less than 70 beats per minute. n The presence of severe coronary artery calcification is the only independent predictor of nondiagnostic coronary CT angiography; an Agatston score cutoff of about 600 shows the best predictive accuracy for performing diagnostic coronary CT angiography. n Preoperative invasive coronary angiography (ICA) can be safely omitted in patients without significant CAD (defined as .50% stenosis) by using coronary CT angiography. Radiology: Volume 258: Number 2—February 2011

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disease (6,7). Thus, the technique has been applied in the preoperative screening of noncoronary cardiovascular surgery (8,9), although initial reports are limited to patients with valvular heart disease, in regular sinus rhythm. In the largest study to date (10), patients with atrial fibrillation also were included. All these studies, however, consist basically of a comparison between ICA and coronary CT angiography, without testing the actual value of coronary CT angiography in terms of avoiding routine ICA in these patients. The purpose of the present study was to assess the usefulness of preoperative coronary CT angiography in the detection of CAD in nonselected patients scheduled to undergo noncoronary cardiovascular surgery to avoid unnecessary ICA.

Materials and Methods One author (P.C.) is supported in part by a research grant from Toshiba Medical Systems–Spain. That author has not received any remuneration for this study. The research grant from Toshiba Medical Systems–Spain was only to support the accommodations of that author in Barcelona during this study. Any industry gave support specifically for the study reported in our article. The authors are not employees of or consultants for any medical or pharmaceutical company, and they have no conflicts of interest. The authors had exclusive control of the data and the information submitted for publication.

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Study Population and Protocol This study protocol was approved by the institutional review board, and all patients gave written informed consent before entering the study. The inclusion criteria were an established indication of noncoronary cardiovascular surgery with need for preoperative ICA (1,2) and the consent of the patient to participate in the study. As exclusion indicators, we considered the accepted contraindications (11) to coronary CT angiography, except atrial fibrillation. A total of 161 consecutive patients were considered for the study. Seven patients were excluded because of history of reaction to iodine-containing contrast agents (n = 1), serum creatine level greater than 1.5 mg/dL (n = 4), body mass index greater than 40 kg/m2 (n = 1), or inability to maintain a breath hold of 10 seconds (n = 1). Thus, a group of 154 patients entered the study. There were no patients with previous coronary stent placement. According to the study protocol, preoperative ICA was not performed in those patients with absent or nonsignificant CAD (vessel obstruction ⱕ 50%) at coronary CT angiography. In case of luminal narrowing of more than 50% or in those patients with nondiagnostic coronary CT angiographic studies, ICA was subsequently performed. Perioperative monitoring was performed from the start of the surgical

Published online before print 10.1148/radiol.10100384 Radiology 2011; 258:426–434

Implications for Patient Care n Coronary CT angiography is a useful preoperative test for safely avoiding ICA in most of the patients scheduled to undergo noncoronary cardiovascular surgery. n Coronary CT angiography provides additional anatomic information on extracoronary structures that may be relevant in relation to the surgical procedure.

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Abbreviations: CAD = coronary artery disease ECG = electrocardiography ICA = invasive coronary angiography Author contributions: Guarantors of integrity of entire study, P.C., R.L., F.C., J.M.P., G.P.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, P.C., R.L., A.H., X.A., D.V., A.B., J.M.P.; clinical studies, all authors; statistical analysis, P.C.; and manuscript editing, P.C., R.L., A.H., J.M., X.A., A.B., S.P., F.C., J.M.P., G.P. See Materials and Methods for pertinent disclosures.

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procedure until hospital discharge. Immediately after intervention and during the intensive care stay (48–72 hours), patients were monitored with continuous 12-lead electrocardiography (ECG), intraarterial blood pressure, and pulse oximetry. Moreover, serial measurements of serum cardiac biomarkers (creatine kinase-MB fraction and cardiac troponin I level) were obtained during this period. During the remaining hospitalization period, ECG and blood pressure were monitored routinely. After hospital discharge, any adverse cardiovascular event defined as acute coronary syndrome (12) or death secondary to acute coronary syndrome, arrhythmias, or cardiac failure was registered from the medical records and, when necessary, by personal phone call.

Coronary CT Angiography: Technical Aspects Coronary CT angiographic examinations were performed with a 64–detector row scanner (Aquilion; Toshiba Medical Systems, Otawara, Japan). In all patients, an unenhanced scan was performed before coronary CT angiography to assess the total coronary calcium burden. This scan was prospectively triggered at 70% or 75% of the R-R interval and performed by using the following scanning parameters: collimation, 4 3 3.0 mm; gantry rotation time, 400–450 msec; tube voltage, 120 kV; and tube current, 200 mA. For contrast material–enhanced scanning, collimation was 64 3 0.5 mm and rotation time was 400 or 450 msec, depending on heart rate. Median tube current and voltage were 320 mA (range, 300–400 mA) and 120 kV (range, 100– 135 kV, in one patient with body mass index . 30 kg/m2), respectively. The total amount of contrast material (Xenetix 350; Guerbet, Aulnay-sous-Bois, France) was determined by the flow rate (in milliliters per second) multiplied by the time of image acquisition (in seconds), plus an additional 10 mL as a safeguard. The average dose was 79 mL 6 13.4 (standard deviation) (range, 50– 120 mL), followed by a saline flush of 40 mL; both were injected at a rate of 5.3 mL/sec 6 0.7 (range, 4–6 mL/sec). The bolus tracking technique was used 428

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to time the scan, with a threshold attenuation of 130 HU in the ascending aorta for initiating the scan acquisition. Of the 154 patients, 141 (92%) received 1 mg of lorazepam orally 60 minutes before the CT scan (8) to avoid potential tachycardia due to stress. In 59 patients with a heart rate greater than 70 beats per minute, intravenous b-blocker therapy (metoprolol tartrate, 2.5–10 mg) was given before the CT scan. Eleven patients with a heart rate less than 55 beats per minute and blood pressure 105/80 mm Hg or higher after receiving intravenous b-blocker therapy received additional sublingual nitroglycerin (0.4 mg) to obtain coronary dilatation if a great increase of heart rate (.70 beats per minute) and/or blood pressure decrease (,100/70 mm Hg) were not expected with it. Radiation doses were estimated by using previously described methods (13). No ECG x-ray modulation was applied because of the lack of this option in our system at the time of the study. Care was taken, however, to minimize radiation dose by using adequate tube voltage (100 Kv) and tube current (300 mA) in patients with body weight less than 90 kg. The effective radiation dose was 14.2–15.9 mSv, derived from the summed dose–length product multiplied by the European Working Group for Guidelines on Quality Criteria in Computed Tomography conversion coefficient (k = 0.014 mSv/[mGy · cm]) (14).

Coronary CT Angiography: Image Reconstruction and Analysis For coronary CT angiography, the acquired volume was reconstructed with a section thickness of 0.5 mm, a reconstruction interval of 0.3 mm, and a field of view of 180–210 mm and by using a medium and, if necessary, a sharper kernel. Images were reconstructed with retrospective ECG gating to obtain motionfree images. We considered diagnostic coronary CT angiographic examination (15) that which enables confirming or ruling out significant CAD. If nondiagnostic image quality was obtained, additional data sets were reconstructed in the end-systolic phase, which was particularly the case in those patients without

controlled atrial fibrillation less than 70 beats per minute. In 48 cases, a manual edition of the ECG was required for the reconstruction of the images, sometimes to improve image quality in patients with atrial fibrillation and high variability of the R-R intervals or to remove extra systoles. If the image quality was not enough to confirm or exclude CAD at the end of imaging reconstruction and postprocessing, we deemed the coronary CT angiogram to be nondiagnostic. For evaluating extracardiac structures, an additional reconstruction was performed with a larger field of view. The Agatston score (16) was used to quantify coronary calcium. A calcified lesion was defined as an area of three or more connected pixels greater than 130 HU and was expressed as Agatston score. All data sets were independently analyzed by two observers (R.L., 8 years of experience in coronary CT angiography; P.C., 6 years of experience in coronary CT angiography) on an offline workstation (Vitrea2; Vital Images, Plymouth, Minn) by using a modified 17-segment American Heart Association classification (17). The axial sections were initially evaluated for the presence of significant CAD, and additional multiplanar reconstructions and curved multiplanar reformation were used for coronary evaluation. Significant coronary disease was defined as greater than 50% stenosis in two orthogonal longitudinal views from the coronary CT angiographic examination, with a proximal nondiseased region of the same arterial segment as a reference. Obstruction of 50% or less was considered nonsignificant CAD, and when measurements of coronary lesions were not readily obtainable, the case was deemed as nondiagnostic. Disagreement between observers was resolved by consensus in a joint reading.

ICA Studies ICA was performed before surgery in those patients with coronary stenosis of 50% or greater at coronary CT angiography and also in cases with nondiagnostic studies. ICA and coronary CT angiography were performed within a time frame of less than 3 months. One

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experienced cardiologist, unaware of the results of coronary CT angiography, analyzed all coronary segments by using a modified American Heart Association classification (17). Segments were classified as normal, nonsignificant disease (ⱕ50% stenosis), or significant CAD (.50% stenosis). These stenoses were evaluated in two orthogonal planes.

Statistical Analysis General characteristics of the study sample were expressed as means 6 standard deviations for continuous variables. The Agatston score was shown as median and interquartile range, because it was not normally distributed. Categoric variables were presented as percentages. Spearman rank correlation coefficient was calculated for correlation between Agatston score and age and significant CAD. An unpaired two-sided Student t test or Mann-Whitney U test and x2 or Fisher exact tests were utilized to compare continuous and categoric variables, respectively, between diagnostic and nondiagnostic coronary CT angiographic groups. P values of less than .05 were considered to indicate statistically significant differences. All P values were two-sided. On the basis of the significance of bivariate analysis (variables with P , .1 were included) between diagnostic and nondiagnostic coronary CT angiographic groups and some especially relevant variables, a multiple logistic regression was performed to determine the independent predictors of nondiagnostic coronary CT angiography. The exclusion criterion of variables for this backward strategy was P value greater than .10. A receiver operating characteristic curve analysis was carried out to obtain the Agatston score with the highest diagnostic accuracy or Youden index (higher sensitivity and specificity to obtain diagnostic coronary CT angiography) and to identify the patients who would probably require ICA for nondiagnostic CT angiography or significant CAD at coronary CT angiography. Kaplan-Meier curves were used to evaluate possible events at follow-up. Statistical analysis was performed by using software (SPSS, version 15.00 for Windows, SPSS, Chicago, Ill; STATA, version Radiology: Volume 258: Number 2—February 2011

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Figure 1

Figure 1: Flow diagram shows distribution of patients according to the results of noninvasive coronary multidetector CT angiography (CCTA). NCCVS = noncoronary cardiovascular surgery.

11.1 for Windows, Stata, College Station, Tex).

Results Of the 154 patients included in the study group, 21 were excluded because surgery was not performed within the time frame of the study. Thus, a total of 133 patients (73 women; mean age, 65 years 6 11) were included in the study (Fig 1). The baseline characteristics of the patients are summarized in Table E1 (online). Eleven (8%) of 133 patients presented with anginal pain at clinical evaluation. Of note, 45 (34%) of 133 patients presented with atrial fibrillation (Fig 2), and two (1.5%) of 133 patients had an implanted pacemaker. Heart rate during scanning was 69 beats per minute 6 14. Prescan b-blocker therapy was given to 59 (44%) of 133 patients. Coronary CT angiography was successfully performed in all cases without complications. The amount of coronary artery calcium, expressed as Agatston score, was 51 (median) with interquartile range of 0–471 (range, 0–3956). We found correlation between age and Agatston score (rs = 0.53; P , .001), as well as between Agatston score and significant CAD (rs = 0.51; P , .001). More specifically, a clear association was seen between patients with a calcium score in a percentile of 75 or higher and significant CAD (18).

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In our trial, we found that significant CAD was 14-fold more prevalent in the subgroup of 35 patients within the percentile of 75 or higher than in patients below this percentile. Coronary CT angiography was diagnostic (Fig 3a–3c) in relation to the presence or absence of significant CAD in 108 (81%) of 133 patients. Ninety-three (86%) of these 108 patients showed no significant CAD, with noncoronary cardiovascular surgery then being performed without preoperative ICA or any other diagnostic test. Significant CAD at coronary CT angiography was present in 15 (11%) of 133 patients: six cases of aortic stenosis, four of mitral regurgitation, three of other rheumatic valvular diseases, and two of aortic wall disease. Of the 11 patients with angina, eight had aortic stenosis, and only one showed significant coronary artery lesions at coronary CT angiography. Those 15 patients with significant CAD at coronary CT angiography underwent preoperative ICA, results of which confirmed the severity of the lesions in 11 of them and showed obstruction of less than 50% in the remaining four patients. Nondiagnostic coronary CT angiographic studies (Fig 3d) occurred in 25 (19%) of 133 patients and were because of severe calcifications (11 patients), motion artifacts (eight patients), or inadequate vessel opacification (six patients). 429


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Analysis of Variables Related to Diagnostic Adequacy of Coronary CT Angiography Parameter Demographics Patients Women Age (y)* Body mass index (kg/m2)* Cardiovascular risk factor Hypertension Diabetes Dyslipidemia Smokers Known CAD CAD family history Indication for surgery Aortic stenosis Mitral regurgitation Mitral stenosis Plurivalvular disease Congenital disease Aortic insufficiency Aortic wall disease Heart rhythm Sinus and pacemaker Atrial fibrillation Heart rate (beats/min)* LVEF (%)* Median Agatston score† Contrast medium Rate (mL/sec)* Volume (mL)*

Diagnostic Coronary CT Angiography

Nondiagnostic Coronary CT Angiography

P Value

108 (81.2) 58 (79.5) 64.4 6 11.2 26.3 6 4.1

25 (18.8) 15 (20.5) 67.2 6 9.5 27.3 6 2.5

… .569 .252 .129

46 (74.2) 16 (76.2) 29 (72.5) 31 (81.6) 5 (83.3) 4 (80)

16 (25.8) 5 (23.8) 11 (27.5) 7 (18.4) 1 (16.7) 1 (20)

.053 .546 .092 .944 .891 .944

29 (72.5) 31 (88.6) 14 (77.8) 13 (86.7) 4 (66.7) 13 (100) 4 (66.7)

11 (27.5) 4 (11.4) 4 (22.2) 2 (13.3) 2 (33.3) 0 2 (33.3)

.092 .194 .746 .736 .314 .127 .314

72 (81.8) 36 (80) 69.6 6 14.5 58.7 6 13 10 (0–218.5) 5.4 6 0.7 79 6 14

16 (18.2) 9 (20) 69.9 6 11.8 58.5 6 12.9 1089 (505.5–2315.5)

.800 .800 .931 .936 .0001

5.2 6 0.9 76.6 6 10.5

.315 .416

Note.—Unless otherwise indicated, data are numbers of patients, with percentages in parentheses. LVEF = left ventricular ejection fraction. * Data are means 6 standard deviations. †

Data in parentheses are interquartile ranges.

Patients with nondiagnostic studies had aortic valve disease (n = 11), mitral stenosis (n = 4), mitral regurgitation (n = 4), other rheumatic valvular diseases (n = 2), atherosclerotic aortic disease (n = 2), or congenital heart disease (n = 2). Variables potentially related to image quality of a coronary CT angiogram were analyzed according to the diagnostic performance of the CT examinations (Table). Three maximum exploratory models with three variables were considered in the multivariate analysis of logistic regression: Agatston score and hypertension as constant variables and dyslipidemia, aortic stenosis, and atrial fibrillation as interchangeable variables (model 1: Ag430

atston score, hypertension, and dyslipidemia; model 2: Agatston score, hypertension, and aortic stenosis, both on the basis of the significance of bivariate analysis; model 3: Agatston score, hypertension, and atrial fibrillation in relation to the clinical interest). In the three models, only the Agatston score remained as independent predictor of nondiagnostic coronary CT angiography (odds ratio = 1.002; 95% confidence interval: 1.001, 1.003; P = .001). The cutoff with the highest sensitivity and specificity (Youden index) for diagnostic coronary CT angiography, as obtained from receiver operating characteristic curve analysis, was 579 (Fig 4). Patients with nondiagnostic

coronary CT angiographic studies were subsequently referred for preoperative ICA, results of which showed significant CAD in five patients and nonsignificant disease in 20. Thus, from the total study group of 133 unselected patients, preoperative ICA was avoided in 70% of them (93 of 133 patients). In those 40 patients referred for ICA, complications of the procedure appeared in two (5%) of 40 patients in the form of local hematoma at the puncture site requiring blood transfusion. None of the patients who underwent surgery without ICA had pre- or postoperative ischemic complications due to a potentially missed diagnosis of CAD at coronary CT angiography. There were no differences in cardiac events, defined as acute coronary syndrome or death secondary to acute coronary syndrome, arrhythmias, or cardiac failure, among patients who had undergone or who had not undergone preoperative ICA (P = .355). These postoperative cardiac events occurred in 15 (11%) of 133 patients. Fourteen patients died during the hospital stay of the following causes: four because of refractory hypercoagulable state; four because of a nosocomial infection; four because of severe right ventricular dysfunction, as evidenced at echocardiography and because of preoperative pulmonary hypertension with right ventricular overload; and two after a major neurologic event. Those patients who died because of right ventricular dysfunction had a preoperative predicted death rate greater than 30% according to the BernsteinParsonnet score (19), preoperative right ventricular dysfunction and/or severe calcification of the mitral ring. One case of dissection of both coronary ostia was attributable to malposition of a prosthetic device in the aortic annulus and could be repaired successfully. No additional events were observed in the clinical follow-up (median, 20 months; interquartile range, 11–25 months), as shown by the KaplanMeier curves for survival free of events (long rank = 0.389) (Fig 5). Of note, relevant noncardiac incidental findings were detected on two coronary CT angiographic studies. A

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case of lung neoplasm was detected in the topogram of the study and proved to be a squamous cell carcinoma. A case of thymoma was seen in the restricted field of view of the coronary CT study, and it was resected during the cardiac intervention.

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Figure 2

Discussion The findings of the present study can be summarized as follows: First, preoperative routine ICA can be safely avoided in a considerable number of patients scheduled to undergo noncoronary cardiovascular surgery by use of coronary CT angiography; second, the presence of a controlled atrial fibrillation does not preclude performing diagnostic coronary CT angiographic examination; third, an Agatston score of coronary calcification higher than 579 significantly increases the likelihood of a subsequent nondiagnostic coronary CT angiography. The performance of ICA as a screening preoperative test before major noncoronary cardiovascular surgery in patients at risk for CAD is recommended (1,2). The rationale for this approach lies in the proved adverse prognosis after surgery in patients with undetected CAD (20–22) and in the reduction in terms of mortality observed when coronary revascularization is performed simultaneously with noncoronary cardiovascular surgery (5,23). Although noninvasive tests for inducible ischemia could represent an alternative to ICA, its usefulness is limited in practice because of a proved suboptimal predictive value of postoperative complications in these patients (24,25). As an invasive procedure, ICA is costly and carries a small but definite risk of complications (1.5%) and even a certain mortality risk (0.15%), and these numbers are higher when the population involved has an increased associated comorbidity, as is the case in those patients scheduled to undergo noncoronary cardiovascular surgery (26). Furthermore, most of these patients will have normal results at ICA examination; the prevalence of significant CAD in these patients has been reported to range between 10% and 20% (27). Radiology: Volume 258: Number 2—February 2011

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Figure 2: Coronary CT angiographic results in patient with a dilated left atrium and atrial fibrillation with mean heart rate of 73 beats per minute at coronary CT angiographic acquisition. (a) Volume-rendered CT image (left anterior oblique view with cranial angulation) shows the arteries: left main (LM), left anterior descending (LAD), first diagonal (1-D), second diagonal (2-D), left circumflex (LCx), and first and second marginal obtuse branches (1-MO, 2-MO). (b) Volume-rendered CT image (right anterior oblique view with cranial angulation) shows the arteries: right coronary artery (RCA), marginal acute branch (MAb), left anterior descending (LAD), and second diagonal (2-D). (c) Curved multiplanar reconstruction of left anterior descending coronary. (d) Maximum intensity projection of right coronary artery.

Because coronary CT angiography has recently emerged as a valuable noninvasive tool for the diagnosis of CAD in symptomatic patients with low to intermediate pretest risk (6,7), it seems appropriate to apply the technique to rule out CAD in patients scheduled to undergo noncoronary cardiovascular surgery. Some previous studies (8–10) have shown a good correlation between coronary CT angiographic and ICA results in selected groups of patients submitted to undergo noncoronary cardiovascular surgery. Of note, in our study, patients did not undergo preoperative ICA if deemed to be free of significant CAD after diagnostic coronary CT angiographic examination. Most important, none of

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these patients had peri- or postoperative complications potentially because of CAD, thus proving the safety of this approach. ICA was performed, in addition to coronary CT angiography, in a total of 40 patients. In those with nondiagnostic coronary CT angiographic studies, ICA results showed a relatively low (five of 25) prevalence of significant CAD. In most of those patients catheterized because of apparently significant CAD at coronary CT angiography (11 of 15), severity of CAD was confirmed. This is in agreement with the reported suboptimal positive predictive value of coronary CT angiography for defining significant coronary artery lesions (28). In practice, however, this is not a major 431


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Figure 3

Figure 3: Noninvasive coronary multidetector CT angiographic images of diagnostic categories. (a) Normal left anterior descending coronary artery (arrow). (b) Left anterior descending coronary artery with nonsignificant stenosis (arrows). (c) Right coronary artery with a significant stenosis (a total occlusion of the midpart of the right coronary artery [arrows]). Top right: ICA image. (d) Coronary CT angiogram is nondiagnostic because of severe calcification and shows significant stenosis (arrows) on ICA image (far right).

limitation in the setting of noninvasive preoperative screening for CAD, where it is more relevant to avoid underdiagnosis of CAD rather than overdiagnosis. The consequence will be that a small proportion of patients without significant CAD will still be referred to undergo ICA. Most important, preoperative coronary CT angiography provides additional information about the thoracic aorta and other mediastinal structures, which is relevant for the cardiac surgeon’s choice (29,30) of cannulation and crossclamping sites. The consecutive recruitment of subjects without exclusions due to atrial fibrillation, which was present in nearly half of our population, is also important. Atrial fibrillation has been traditionally 432

considered a relative contraindication to coronary CT angiographic examination (11,31). However, when the mean heart rate is appropriately controlled by means of medical therapy, the deleterious effect of an irregular heart rhythm on the quality of the images is notably minimized (10,32,33). The availability of systems for editing ECG synchronization improves the retrospective reconstruction in cases of arrhythmia. This is proved by the results of our study, which showed a similar proportion of nondiagnostic studies in patients with sinus rhythm and in those with controlled atrial fibrillation (Table). Nondiagnostic coronary CT angiography accounted for 19% of patients studied. The amount of coronary artery

calcium, quantified by means of the Agatston score, was the determinant for a diagnostic study, with a cutoff of 579 being the best predictor. In view of these data, it could be questionable to proceed with noninvasive coronary CT angiography after coronary calcium scanning yielded an Agatston score higher than this value. For example, a rise in the Agatston score from 579 to 1000 or 1500 increases two- and sixfold, respectively, the risk of nondiagnostic coronary CT angiography. As with any other procedure that involves CT, radiation associated with coronary CT angiography is an issue of concern. In particular, the estimated doses of radiation in our study proved to be significantly higher than those

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Figure 4 Figure 4: Receiver operating characteristic curve for a model created to assess the ability to interpret coronary CT angiograms in this clinical setting. AS = Agatston score, AUC = area under the receiver operating characteristic curve, CI = confidence interval, SD = standard deviation.

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erative ICA was safely avoided in those patients without significant CAD. A proportion of nondiagnostic coronary CT angiographic studies still remained, mainly because of severe coronary calcification, and a high Agatston score was the only predictor of an adequate coronary CT angiographic examination. Acknowledgments: We are grateful to the expert advice on statistics of Ignasi Gich, MD, from the Department of Epidemiology of Sant Pau University Hospital and to the Unit of Clinical Biostatistics of Ramón y Cajal University Hospital, in particular to Víctor Abraira, PhD.

References 1. Bonow RO, Carabello BA, Chatterjee K, et al. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease) developed in collaboration with the Society of Cardiovascular Anesthesiologists endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons. J Am Coll Cardiol 2006;48:e1-e148.

Figure 5

2. Vahanian A, Baumgartner H, Bax J, et al. Guidelines on the management of valvular heart disease: The Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology. Eur Heart J 2007;28(2):230–268.

Figure 5: Kaplan-Meier curves for survival-free events after cardiac surgery.

reported for diagnostic ICA (34,35). Strategies to limit radiation dose include reduction of tube current or voltage, which is not always feasible in patients with large body mass, and the use of prospective x-ray tube current modulation, which cannot be used in patients with atrial fibrillation, which is a frequent occurrence in this clinical setting. The new generation of CT systems already available, which are based on a single heart beat volume acquisition, will greatly overcome this limitation by means of an important reduction of radiation (36,37). A potential limitation of the study was that its results cannot be extraRadiology: Volume 258: Number 2—February 2011

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polated to other populations of patients usually submitted to preoperative ICA, as those scheduled to undergo major vascular surgery, in whom the presumably higher prevalence of significant CAD would probably lead to a lower number of avoided ICA studies. A further study particularly addressing this issue is warranted. In conclusion, in patients scheduled to undergo noncoronary cardiovascular surgery, including those with controlled atrial fibrillation, the presence or absence of CAD can be reliably assessed preoperatively by using coronary CT angiography in a majority of cases. Preop-

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