Author + information
- Received March 14, 2007
- Revision received July 2, 2007
- Accepted July 10, 2007
- Published online October 9, 2007.
- W. Bob Meijboom, MD⁎,†,
- Carlos A.G. van Mieghem, MD⁎,†,
- Nico R. Mollet, MD, PhD⁎,†,
- Francesca Pugliese, MD⁎,†,
- Annick C. Weustink, MD⁎,†,
- Niels van Pelt, MD⁎,†,
- Filippo Cademartiri, MD, PhD†,
- Koen Nieman, MD, PhD⁎,
- Eric Boersma, MSc, PhD⁎,
- Peter de Jaegere, MD, PhD⁎,
- Gabriel P. Krestin, MD, PhD† and
- Pim J. de Feyter, MD, PhD, FACC⁎,†,⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Pim J. de Feyter, Erasmus Medical Center, Department of Cardiology and Radiology, Room Hs 207, P.O. Box 2040, 3000 CA Rotterdam, the Netherlands.
Objectives We assessed the usefulness of 64-slice computed tomography coronary angiography (CTCA) to detect or rule out coronary artery disease (CAD) in patients with various estimated pretest probabilities of CAD.
Background The pretest probability of the presence of CAD may impact the diagnostic performance of CTCA.
Methods Sixty-four-slice CTCA (Sensation 64, Siemens, Forchheim, Germany) was performed in 254 symptomatic patients. Patients with heart rates ≥65 beats/min received beta-blockers before CTCA. The pretest probability for significant CAD was estimated by type of chest discomfort, age, gender, and traditional risk factors and defined as high (≥71%), intermediate (31% to 70%), and low (≤30%). Significant CAD was defined as the presence of at least 1 ≥50% coronary stenosis on quantitative coronary angiography, which was the standard of reference. No coronary segments were excluded from analysis.
Results The estimated pretest probability of CAD in the high (n = 105), intermediate (n = 83), and low (n = 66) groups was 87%, 53%, and 13%, respectively. The diagnostic performance of the computed tomography (CT) scan was different in the 3 subgroups. The estimated post-test probability of the presence of significant CAD after a negative CT scan was 17%, 0%, and 0% and after a positive CT scan was 96%, 88%, and 68%, respectively.
Conclusions Computed tomography coronary angiography is useful in symptomatic patients with a low or intermediate estimated pretest probability of having significant CAD, and a negative CT scan reliably rules out the presence of significant CAD. Computed tomography coronary angiography does not provide additional relevant diagnostic information in symptomatic patients with a high estimated pretest probability of CAD.
The estimated pretest probability of having significant coronary artery disease (CAD) in a study population should be taken into account in the evaluation of the diagnostic accuracy of computed tomography coronary angiography (CTCA) to detect or rule out the presence of coronary stenosis. The estimated pretest probability of having obstructive CAD in patients who present with chest pain is related to age, gender, type of chest discomfort, and traditional risk factors. The estimated pretest probability is lowest in younger female patients with nonanginal chest pain and highest in older male patients with typical angina (1).
The diagnostic performance of CTCA has mostly been tested in symptomatic patient populations with a high estimated pretest probability of having significant CAD, and a few studies have reported on the impact of different estimated pretest probabilities on the performance of CTCA (2).
The purpose of this study was to evaluate the diagnostic performance and clinical usefulness of 64-slice CTCA in 254 patients with high, intermediate, or low estimated pretest probability of having significant coronary stenosis.
During a 24-month period, 254 patients presenting with typical angina pectoris, atypical angina pectoris, and nonanginal chest pain who were referred for conventional coronary angiography (CCA) were included into the study. Typical angina was defined as having 3 characteristics: 1) substernal discomfort; 2) that is precipitated by physical exertion or emotion; and 3) relieved with rest or nitroglycerin within 10 min. Atypical angina pectoris was defined as having 2 of 3 of the definition characteristics. Nonanginal chest pain was characterized as 1 or absence of the described chest pain features. The estimated pretest probability for obstructive CAD was estimated using the Duke Clinical Score, which includes type of chest discomfort, age, gender, and traditional risk factors (3,4). Patients were categorized into a low (1% to 30%), intermediate (31% to 70%), or high (71% to 99%) estimated pretest probability group of having significant CAD. No patients with previous history of percutaneous coronary intervention, coronary artery bypass surgery, prior myocardial infarction, impaired renal function (serum creatinine >120 μmol/l), persistent arrhythmias, or known allergy to iodinated contrast material were included. Conventional coronary angiogram was performed before or after the CTCA and served as the standard of reference. The institutional review board of the Erasmus Medical Center Rotterdam approved the study, and all subjects gave informed consent.
Patients with a heart rate exceeding 65 beats/min received additional beta-blockers (50/100 mg metoprolol) 1 h before the computed tomography (CT) examination.
All scans were performed with a 64-slice CT scanner that features a gantry rotation time of 330 ms, a temporal resolution of 165 ms, and a spatial resolution of 0.4 mm3(Sensation 64, Siemens, Forchheim, Germany). A calcium scoring scan was performed with the following parameters: 64 × 0.6 mm collimation, 330 ms rotation time, 120 kV tube voltage, 150 mAs tube current, 3.8 mm/rotation table feed, prospective electrocardiogram (ECG) X-ray tube modulation. Afterward, the CTCA was performed using identical parameters aside from a higher tube current between 850 and 960 mAs and without the use of prospective ECG X-ray tube modulation. The radiation exposure was estimated using dedicated software (ImPACT, version 0.99x, St. George’s Hospital, Tooting, London, United Kingdom).
A bolus of 95 ml of contrast material (400 mgI/ml; Iomeron, Bracco, Milan, Italy) was injected intravenously in an antecubital vein at 5 ml/s, and a bolus-tracking technique was used to synchronize the arrival of contrast in the coronary arteries and the initiation of the scan.
Datasets were reconstructed immediately after the scan after a stepwise approach as previously described (5,6). If necessary, multiple datasets of a single patient were used separately in order to obtain optimal image quality for all available coronary segments.
Quantitative coronary angiography (QCA)
All scans were carried out within 1 week before or after CCA. One experienced cardiologist, unaware of the results of CTCA, identified and analyzed all coronary segments, using a 17-segment modified American Heart Association classification. All segments, regardless of size, were included for comparison with CTCA. Segments were classified as normal (smooth parallel or tapering borders), as having nonsignificant disease (wall irregularities or <50% stenosis), or having significant disease (stenosis ≥50%). Stenoses were evaluated in the worst view, and classified as significant if the lumen diameter reduction exceeded ≥50% measured by validated QCA algorithm (CAAS, Pie Medical, Maastricht, the Netherlands).
CT image evaluation
One observer analyzed total calcium scores of all patients using dedicated software. Two experienced observers, a radiologist and a cardiologist, unaware of the results of CCA, evaluated the CTCA data sets on an offline workstation (Leonardo, Siemens) using (curved) multiplanar reconstruction. Segments were scored positive for significant CAD if there was ≥50% diameter reduction of the lumen by visual assessment. Segments distal to a chronic total occlusion were excluded. Interobserver disagreements were resolved by a third reader.
The diagnostic performance of CTCA for the detection of significant coronary artery stenoses as defined by QCA is presented as sensitivity, specificity, positive and negative predictive values with the corresponding 95% confidence intervals (CIs), and positive and negative likelihood ratios (LRs) were calculated. Comparison between CTCA and QCA was performed on 3 levels: patient-by-patient, vessel-by-vessel, and segment-by-segment analysis. A Mantel-Haenszel test was performed to evaluate the trend in sensitivity and specificity relative to the estimated pretest probability for obstructive CAD.
Categorical characteristics are expressed as numbers and percentages, and compared between the 3 groups using the chi-square test. Continuous variables are expressed as means (standard deviation) and compared with 1-way analysis of variance followed by post-hoc Bonferroni correction to adjust for multiple comparisons. If not normally distributed, continuous variables are expressed as medians (25th to 75th percentile range) and compared with Kruskal-Wallis test.
An additional analysis was done to investigate the effect of nesting since repeated assessments within the same patient were made that were not independent observations. A random selection of a single segment per patient was done, and the diagnostic accuracy for detecting significant artery disease was calculated. Interobserver and intraobserver variability for the detection of significant coronary stenosis and agreement between techniques to classify patients as having no, single-, or multivessel disease was determined by κ-statistics.
Patient demographics are shown in Table 1.Additional beta-blockers before CT scanning were administered in 74% (188 of 254) of patients decreasing the mean heart rate from 71 ± 11 beats/min to 59 ± 8 beats/min. The mean scan time was 12.7 ± 1.6 s. Initially, all data sets were reconstructed in the mid- to end-diastolic phase. In 34% of the cases (86 of 254), additional higher quality reconstructions obtained during end systole were used for evaluation.
The estimated radiation exposure using prospective X-ray tube modulation for the calcium score in women and men was 1.8 and 1.4 mSv, respectively. The estimated radiation exposure for the contrast-enhanced scan without prospective X-ray tube modulation was 17.0 mSv in women and 13.4 mSv in men, which is in line with previous reports (7).
Diagnostic performance of 64-slice CTCA: all patients with chest pain
The observed pretest probability of significant CAD, defined as having at least 1 ≥50% coronary stenosis per patient was 50%. The diagnostic performance of CTCA for detecting significant stenoses on a patient level is detailed in Table 2.Eighteen patients with angiographic nonsignificant disease were incorrectly classified as having significant CAD by CT: 17 patients were scored as having single-vessel disease, and 1 patient was misinterpreted as having multivessel disease. Ninety-eight percent (124 of 126) of patients with significant CAD on CCA were correctly identified by CTCA (Fig. 1).The 2 patients in whom the severity of disease was underestimated both showed significant lumen narrowing in the circumflex coronary artery (both 53% diameter reduction, 1 in the proximal and 1 in the midsegment). Forty patients with single-vessel disease were evaluated as having multivessel disease by CTCA due to overestimation of disease severity in other vessels. Agreement between CTCA and QCA on a per-patient (no or any disease) level was very good (κ-value: 0.84), whereas agreement between techniques to classify patients as having no, single-, and multivessel disease was good (κ-value: 0.61).
Diagnostic performance of 64-slice CTCA: patient-by-patient analysis
The analysis comprised 105 (43%) patients with a high estimated pretest probability for CAD, 83 (33%) patients with an intermediate, and 66 (26%) patients with a low estimated pretest probability for CAD. The mean age between patients with high estimated probability and intermediate estimated probability was significantly different from the mean age in the low probability group, and the median calcium score was significantly different in all 3 groups. The mean heart rate was significantly lower in the high estimated probability group compared with those seen in the intermediate and low estimated probability groups (Table 1).
The diagnostic performance of CTCA was different in the patient groups with various estimated pretest probabilities. The specificity showed a trend with a lower specificity in the high estimated pretest probability (p < 0.05, sensitivity p = NS). The diagnostic impact of CTCA on the estimated pretest probability of having significant CAD is shown in Figures 2 and 3.⇓
Diagnostic performance of 64-slice CTCA: vessel-by-vessel analysis
The diagnostic performance of CTCA for the detection of significant lesions on a vessel-based analysis is detailed in Table 2. Two significantly diseased right coronary arteries, 1 left anterior descending artery, and 5 diseased circumflex coronary arteries were incorrectly classified as nonsignificantly diseased by CTCA. Of a total of 1,016 vessels, the severity of a lesion was overestimated in 97 nonobstructive vessels (false positives). The diagnostic performance of the CT scan was different in the 3 subgroups. The specificity showed a trend towards lower specificity in the high estimated pretest probability (p < 0.0001, sensitivity p = NS). Agreement between CTCA and QCA on a per-vessel level was good (κ-value: 0.71).
Diagnostic performance of 64-slice CTCA: segment-by-segment analysis
Overall, 3,647 (of 4,318 potentially available segments) were included for comparison with QCA. Unavailable segments included 547 anatomically absent segments on CCA and 124 segments distal to an occluded coronary segment. Segments were not excluded for reasons such as severe calcifications or poor image quality. The κ-value for interobserver and intraobserver variability was 0.70 and 0.72, respectively. The diagnostic performance of CTCA for detecting significant stenoses is detailed in Table 2. Agreement between CTCA and QCA on a per-segment level was good (κ-value, 0.64).
The severity of 32 significant coronary stenoses was underestimated or missed and classified as nonsignificant by CTCA. Most of these significant lesions (24 of 32) were located in distal segments or in side branches. The severity of 193 nonsignificant lesions was overestimated by CTCA. The diagnostic performance of the CT scan was different in the 3 subgroups with a lower sensitivity (p < 0.05) and a higher specificity (p < 0.0001) in the low pretest probability group.
Analysis on the randomly selected segments resulted in a sensitivity of 92% (24 of 26; 95% CI 73% to 99%), specificity of 93% (212 of 228; 95% CI 89% to 96%), positive predictive value of 60% (16 of 40; 95% CI 43% to 75%), and a negative predictive value of 99% (212 of 214; 95% CI 96% to 100%). The effect of nesting is probably minimal as the result of this analysis is very similar to the results shown in the per-segment analysis (Table 2).
The diagnostic performance of 64-slice CTCA to detect or rule out the presence of significant coronary stenosis has mainly been reported for patients with stable angina pectoris scheduled for invasive CCA, and these studies have shown that CTCA can reliably rule out significant CAD (5,8–10). The majority of these patients presented with a high estimated pretest probability of having significant CAD, and only scant information is available on the diagnostic performance of 64-slice CTCA in patients with a low or intermediate estimated pretest probability of having significant CAD.
In this study, we used the Duke Clinical Score, which incorporates clinical presentation of chest pain, age, gender, and traditional risk factors, to estimate the pretest probability of having significant CAD. Using the LRs of the tests, which were obtained in this study, post-test probabilities were calculated.
The pretest probability of CAD may impact of the diagnostic performance of the CT scan. Indeed, the diagnostic performance of CTCA in the 3 groups was different. The specificity was lower in the high pretest probability group compared with the low pretest probability group, whereas sensitivity was lower in the per-segment analysis in the low pretest probability group. This observation can probably be explained by the higher calcium scores in the higher probability groups, which tend to overestimate the severity of stenosis.
A negative CT scan was present in 75% of the patients with a low estimated pretest probability and in approximately 50% of the patients with an intermediate estimated pretest probability. The negative predictive value of CTCA to exclude significant CAD was excellent in these patients, reducing the estimated post-test probability to zero. Thus, these patients would not need further downstream diagnostic tests. They may be candidates for secondary prevention measures, such as statin therapy in the presence of nonobstructive plaques or could be discharged from further cardiac follow-up in the absence of any visible plaque.
A positive CT scan occurred in approximately 25% and 50% of the patients with a low or intermediate estimated pretest probability, respectively. The number of false-positive outcomes was rather high in these patients, which renders a positive CT scan rather unreliable for clinical decision making. In these patients it may be reasonable to proceed to invasive CCA in the case of left main disease, 3-vessel disease, and in the presence of a critical stenosis in the proximal part of a major coronary artery. In case of vessel disease in distal vessels or side branches, equivocal lesions, or uninterpretable scans, one may consider a noninvasive stress test to determine the functional significance of a doubtful coronary stenosis. A negative functional test may overrule the clinical significance of a (false)-positive CT scan and reduce the need for invasive coronary angiography. A positive functional test may further increase the probability of having significant CAD and should be followed by invasive coronary angiography and coronary revascularization if symptoms are not alleviated by the antianginal mediation. However, further studies are necessary to evaluate the diagnostic value of the combination of functional data from a stress test with the anatomical data provided by CTCA.
In the high estimated pretest probability group, a negative CTCA reduced the estimated post-test probability to 17%, whereas a positive CTCA increased the estimated post-test probability to as high as 96%. Given the high estimated pretest probability of significant CAD in this group, the majority of these symptomatic patients are likely to proceed to invasive CCA even if CTCA is negative, since the post-test probability of significant CAD was still >10%. Computed tomography coronary angiography, therefore, appears to be of limited clinical value in the evaluation of the high estimated pretest probability group. Assessment for the presence of myocardial ischemia with a functional test may be more appropriate in this situation.
The studied patients were not a prospective, consecutive group of patients. However, selection was not based on particular patient demographics, but rather on the availability of the 64-slice CT scanner for the examination of cardiac patients. The rather high estimated radiation exposure of 64-slice CTCA (17 to 13.4 mSv) as compared with CCA (3 to 6 mSv) is of concern (7). In this study we did not use prospective ECG X-ray tube modulation, which can significantly reduce radiation exposure, but requires a regular heart rhythm and limits the possibility of reconstructing images in the end-systolic phase. In our study end-systolic data sets provided optimal image quality in 34% of patients.
Currently, there is no validated software available able to quantify the degree of stenoses. So far, the severity of coronary stenosis as assessed by CT is rather crudely visually estimated as more or less than 50% luminal diameter stenosis.
- Abbreviations and Acronyms
- coronary artery disease
- conventional coronary angiogram
- confidence interval
- computed tomography
- computed tomography coronary angiography
- likelihood ratio
- quantitative coronary angiography
- Received March 14, 2007.
- Revision received July 2, 2007.
- Accepted July 10, 2007.
- American College of Cardiology Foundation
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