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Original Research |
1 Department of Radiology, Massachusetts General Hospital Cardiac MR CT PET
Program and Harvard Medical School, 100 CPZ 400, Boston, MA 02114.
2 Division of Cardiology, Massachusetts General Hospital and Harvard Medical
School, Boston, MA.
3 Department of Emergency Medicine, Massachusetts General Hospital and Harvard
Medical School, Boston, MA.
Received December 29, 2005;
accepted after revision May 16, 2006.
This study was supported in part by the New York Cardiac Center, New York,
NY; GE Healthcare, Princeton, NJ; and Siemens Medical Solutions, Forchheim,
Germany
Abstract
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SUBJECTS AND METHODS. We studied 40 patients (53% men; mean age, 57 ± 13 years) with chest pain who were awaiting hospital admission to rule out an acute coronary syndrome (ACS) despite the absence of diagnostic ECG changes and normal cardiac enzymes on emergency department presentation. Patients underwent contrast-enhanced MDCT before hospital admission. Afterward, patients received standard clinical care. All physicians involved in the patients' care were blinded to the results of MDCT. An expert panel established the presence or absence of ACS based on American Heart Association (AHA) guidelines. The MDCT images were evaluated for the presence of significant coronary artery stenosis (diameter reduction > 50%) and were used to make a triage decision.
RESULTS. All five patients (12.5%) with ACS (one with non-ST elevation myocardial infarction, four with unstable angina pectoris) had at least one significant coronary stenosis on MDCT (sensitivity, 100% [95% CI, 49-100%)]. ACS was ruled out in 35 patients (87.5%). Significant coronary stenosis was excluded in 26 of the 35 patients without ACS by MDCT (specificity, 74% [CI, 75-88%]), potentially saving 70% of unnecessary hospital admissions.
CONCLUSION. MDCT-based detection of significant coronary stenoses has tremendous potential to decrease the number of unnecessary hospital admissions, without reducing appropriate admission rates, in patients with chest pain who have nondiagnostic ECG results and normal cardiac enzymes. These results are likely to further improve with advances in MDCT technology.
Keywords: acute coronary syndrome • cardiac imaging • CT coronary arteriography • coronary artery disease • emergency radiology • MDCT • patient management
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Unfortunately, triage decisions guided by an estimate of patient risk for acute coronary syndrome (ACS) using a variety of clinical predictors is often ineffective, especially in patients with convincing clinical presentation but normal initial cardiac enzymes and normal or nondiagnostic ECG. The predictive value of single variables [4-6] such as patient age, sex, presence of risk factors, and biochemical markers for adverse outcomes is limited [7-9]. Moreover, the rate of missed ACS remains unacceptably high (2%) and is associated with a twofold increased risk of mortality [10-14], contributing to the low threshold of emergency department physicians to admit patients with chest pain. Because of the limited ability to correctly risk stratify patients with acute chest pain, the potentially fatal consequences of missed ACS, and the resulting liability issues (20% of emergency department malpractice dollar losses) [10], more than 2 million patients with acute chest pain are admitted to the hospital without developing an ACS [11, 13]. Because 60% of patients eligible for early emergency department discharge are actually admitted to the hospital [15], the number of potentially unnecessary hospital days (per 100 patients enrolled) is high, ranging from 65 in New Zealand to 839 in Germany [14].
The ability to quickly and accurately exclude a potentially life-threatening coronary cause of chest pain would improve patient care and potentially reduce health care costs significantly.
MDCT systems with submillimeter spatial and high temporal resolutions that permit motion-free imaging of the coronary arteries are becoming available in many emergency departments around the United States. A growing number of studies provide sufficient evidence that MDCT is highly accurate for detecting significant coronary stenoses (> 50% luminal narrowing) in the major epicardial coronary arteries compared with invasive selective coronary angiography [16-21]. Recent data indicate the feasibility of 64-MDCT to detect stenosis in smaller side branches with a sensitivity of 78-100%, specificity of 96-100%, positive predictive value of 87-100%, and negative predictive value of 97-100% [22, 23].
Noninvasive assessment of coronary artery disease is not part of the standard clinical care of patients with acute chest pain. Conceivably, implementation of noninvasive coronary imaging in the emergency department could influence existing paradigms for triage and care of patients with acute chest pain by significantly reducing the number of unnecessary hospital admissions.
The aim of this pilot study was to determine the accuracy of the noninvasive detection of significant coronary artery stenosis by MDCT, and to ascertain the feasibility of using the findings for triage decision making in patients with acute chest pain who are awaiting hospital admission despite normal initial cardiac enzymes and normal or nondiagnostic ECG on emergency department presentation.
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Patients
Between September 2004 and March 2005, we screened patients in the
emergency department of a tertiary care academic hospital awaiting admission
to the hospital because of suspected acute cardiac ischemia. Because of
restricted funding, study enrollment was limited to only 2 days per week from
9 am to 5 pm during the weekdays. We included patients with more than 5
minutes of chest pain at rest or during exertion within the previous 24 hours
that was suspected to be cardiac in origin, who were able to perform a
breath-hold of 10-15 seconds, and who were older than 18 years. We excluded
patients with either troponin-I or creatine kinase, myocardial bound (CKMB)
enzyme elevation on presentation; those with new diagnostic ECG changes
(ST-segment elevation or depression > 1 mm or T-wave inversion > 3 mm)
in at least two anatomically consecutive leads; those with evidence of
hemodynamic or clinical instability (systolic blood pressure < 80 mm Hg,
atrial or ventricular arrhythmias, persistent chest pain despite adequate
therapy); and patients with known allergy to iodinated contrast agent or serum
creatinine more than 1.3 mg/dL.
MDCT imaging was initiated after emergency department staff made the decision to admit the patient to the hospital although the patient's initial ECG was interpreted as nondiagnostic and the cardiac biomarkers were confirmed to be normal. At this time, the physicians caring for the patient provided an estimate of the probability of the patient having ACS (0-100%) based on the data available at initial triage (patient history, risk factors, clinical presentation). This information was collected from the emergency department attending physician in 16 patients and from a third- or fourth-year emergency department resident in 24 patients when the decision was made to admit the patient to the hospital floor for further evaluation.
All physicians involved in the standard clinical care of the patients remained blinded to the result of the MDCT imaging. Afterward, patients received standard clinical care to rule out an ACS during hospitalization including serial ECGs, cardiac enzyme tests, stress perfusion imaging, cardiac catheterization, and other diagnostic tests. The institutional review board of the Massachusetts General Hospital approved the study protocol.
MDCT Imaging
MDCT protocol—MDCT imaging was performed with a Sensation
16- or Sensation 64-MDCT scanner (Siemens Medical Solutions). In preparation
for the scan, all patients with a heart rate greater than 60 beats per minute
received a ß-blocker (5-15 mg metoprolol, IV) unless their systolic blood
pressure was greater than 100 mm Hg or other contraindications were present.
All image acquisitions were performed during a breath-hold in inspiration.
Imaging parameters for the 16-MDCT scanner were: slice collimation, 16 x 0.75 mm; gantry rotation time, 420 milliseconds; tube voltage, 120 kV; effective tube current, 500 milliampere seconds. For the 64-MDCT scanner, the parameters were: slice collimation, 64 x 0.6 mm; gantry rotation time, 330 milliseconds; tube voltage, 120 kV; effective tube current, 850 milliampere seconds. To lower radiation exposure, the technique of tube current modulation was used in all patients. A contrast agent (iodixanol 320 g/cm3, Visipaque, GE Healthcare) was injected IV at a rate of 4 or 5 mL/s to ensure opacification of the coronary artery lumen.
Overlapping transaxial images were reconstructed using a medium-sharp convolution kernel (B35 f) with an image matrix of 512 x 512 pixels, slice thickness and increment of 1.0/0.5 mm or 0.75/0.4 mm using an ECG-gated half-scan algorithm with a resulting temporal resolution of 210/165 milliseconds in the center of rotation. Image reconstruction was retrospectively gated to the ECG. The position of the reconstruction window within the cardiac cycle was individually optimized to minimize motion artifacts. On average, three data sets per patient were reconstructed.
MDCT image evaluation and analysis—Reconstructed MDCT data sets of all patients were transferred to an offline workstation (Leonardo, Siemens Medical Solutions) and made anonymous by a study coordinator. One highly trained radiologist, who had experience with interpreting more than 500 coronary CT examinations, including 150 with correlation to selective invasive coronary angiography, and who was blinded to the patient's name, clinical history, and outcome, reviewed the MDCT examinations.
For the detection of significant coronary artery stenosis, a segment model
of the American Heart Association (AHA), with the addition of the posterior
left ventricular branch as segment 16 and the intermediate branch as segment
17, was used [24]. Coronary
segments were identified relative to the origin of side branches. The MDCT
data sets were assessed qualitatively for the presence of significant luminal
obstruction (
50%) within all coronary segments, including side branches
[17,
19,
25]. Assessment was performed
on original axial source images, thin slice (5 mm) maximum-intensity
projections, multiplanar reformat reconstructions orthogonal and perpendicular
to the vessel centerline, and short-axis cross-sectional reconstructions (1-mm
thick). The MDCT interpreter rated the overall image quality (limited, good,
or excellent) and noted the presence and source of artifacts. The MDCT
interpreter determined whether a significant coronary stenosis was present or
could not be excluded or was absent. MDCT was positive if at least one
significant coronary artery stenosis per patient was detected or could not be
excluded. MDCT was negative when the presence of any significant stenosis in a
patient could be excluded
[17].
The duration of MDCT scanning, use of ß-blockers and nitroglycerin, amount of contrast material, radiation dose, body mass index, and patient's heart rate were recorded.
Clinical Variables and Endpoints
We prospectively collected data about each patient's demographics, risk
factor profile, and clinical course, including onset of symptoms, presentation
to the emergency department, triage decision in the emergency department,
transfer to the hospital floor, and hospital discharge. Medical records were
reviewed to obtain data about all diagnostic tests. Presence of risk factors
was established from actual measurements obtained during the hospitalization
(i.e., hypertension, hypercholesterolemia, and diabetes mellitus).
To establish the presence or absence of ACS, a panel of a two physicians (one cardiologist and one emergency department physician) reviewed the data forms and all medical records pertaining to the hospital admission of enrolled patients, including physician notes, discharge summary, cardiac biomarkers, ECGs, and results of stress testing or coronary angiography. The reviewers were blinded to the findings of MDCT. Disagreement was solved by consensus [26].
We used prospectively defined categories, based on AHA and American College of Cardiology (ACC) guidelines [4], to validate the diagnosis of ACS during the index hospitalization. The first category was ST-segment elevation myocardial infarction (STEMI), which was defined by clinical symptoms suggestive of ACS with a new finding of transient (> 20 minutes) ST-segment elevation greater than 1 mm in at least two anatomically contiguous leads, and by elevated serial levels of troponin-I (> 0.01 mg/dL). Another category was non-STEMI (NSTEMI), which was defined by clinical symptoms suggestive of ACS with a new finding of ST-segment depression greater than 1 mm, T-wave inversion of at least 4 mm in at least two anatomically contiguous leads, or elevated serial levels of troponin-I (> 0.01 mg/dL). The last category was unstable angina pectoris (UAP), which was defined by crescendo angina, angina occurring at rest or after previous myocardial infarction with objective evidence of myocardial ischemia on stress testing, or coronary angiography with more than 50% epicardial coronary stenosis.
Projected Length of Hospital Stay
The length of stay and the number and nature of diagnostic tests were
recorded in the subgroup of patients in whom ACS was excluded by standard care
during their hospitalization and in whom the presence of any significant
stenosis could be excluded by MDCT. To perform a crude comparison of the
length of stay of standard clinical care and a projected length of stay using
an MDCT-based strategy, the time of 2 hours after the MDCT scan was defined as
a potential discharge time.
Statistical Analysis
We determined accuracy, sensitivity, specificity, positive predictive
value, and negative predictive value (with binomial exact 95% CIs) and the
diagnostic odds ratio for the presence of significant stenosis (> 50%
luminal narrowing) in MDCT compared with the discharge diagnosis (ACS vs no
ACS). These analyses were performed for the entire patient cohort and as a
subanalysis for patients who underwent 16-MDCT and 64-MDCT. An unpaired
Student's t test was performed to look for significant differences in
heart rate for 16-versus 64-MDCT examinations and in heart rate for limited
versus good or excellent image quality, and to determine whether heart rate or
body mass index was significantly different in those patients with
false-positive findings by MDCT versus the entire study cohort. To test for
significant differences in image quality between 16- and 64-MDCT, a chisquare
test was performed. To test for a significant difference of the length of stay
for patients receiving standard clinical care versus the projected length of
stay for an MDCT-based strategy, we used a paired Student's t test.
For all tests, a p value of less than 0.05 was considered to indicate
statistically significant differences.
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Clinical Variables and Outcomes
The average time from symptom onset to patient presentation in the
emergency department was 5.0 ± 7.5 hours. Three patients presented more
than 20 hours after symptom onset. Excluding these patients, the average time
from symptom onset to presentation in the emergency department was 3.0
± 2.2 hours. The mean length of stay in the emergency department was
9.3 ± 4.6 hours. All 40 patients were admitted to the hospital and
received standard care for evaluation and treatment of possible acute coronary
syndrome, including serial cardiac enzyme measurement and ECGs followed by
perfusion stress imaging in 18 patients and coronary angiography in seven
patients (as deemed appropriate by the treating physician). The average
clinical pretest probability as assessed by emergency department staff at the
time of triage was 30% ± 24% (range, 1-90%). Five patients (12.5%) were
diagnosed with ACS (one with NSTEMI, four with UAP), whereas ACS was ruled out
in 35 patients (87.5%). The pretest probability of having ACS was not
significantly different between patients with (n = 5) and without ACS
(n = 35) (44% ± 39% vs 28% ± 21%; p =
0.15).
MDCT Imaging
MDCT was performed 5.9 ± 4.9 (mean ± SD) hours after
presentation to the emergency department. The average MDCT procedure time was
5 ± 3 (mean ± SD) minutes. The average time in the CT suite,
including patient preparation and turnover, was 15 ± 5 minutes (mean
± SD) (door-to-door time).
No adverse events occurred, and MDCT imaging was successfully completed in all 40 patients. The first 17 patients underwent MDCT scanning with the 16-MDCT scanner. The subsequent 23 patients underwent MDCT scanning with the 64-MDCT scanner. The mean scanning time was 19 ± 2 seconds and 13 ± 2 seconds, respectively; the mean contrast dose was 80 ± 6 mL and 70 ± 5 mL for 16- and 64-MDCT, respectively. The mean heart rate during the scan was 62 ± 8 beats per minute and was not different for patients undergoing 16-or 64-MDCT (p = 0.85). A total of 22 patients were treated with ß-blockers before MDCT; 12 patients received ß-blockers as part of the initial treatment in the emergency department, and 10 patients received ß-blockers (5-15 mg metoprolol, IV) immediately before the CT examination as part of the study protocol.
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The heart rate in patients with limited image quality was significantly higher than in other patients (66 ± 12 bpm vs 59 ± 6 bpm; p = 0.04). Reasons for impaired image quality were motion artifacts in four patients and severe calcification in four patients.
Findings and Diagnostic Accuracy of MDCT Imaging
In our primary analysis, we evaluated MDCT images for the presence of
significant stenosis (> 50% luminal narrowing). In 26 patients, the
presence of any significant coronary artery stenosis was excluded. In 14
patients, the presence of any significant coronary artery stenosis was either
detected or could not be excluded.
The diagnosis of ACS was made in five patients (12.5%). All five of these patients had at least one significant coronary stenosis by MDCT (sensitivity, 100%; 95% CI, 49-100%; positive predictive value, 38%; 95% CI, 13-65%) (Figs. 1A, 1B, 1C, and 1D). Significant coronary stenosis was excluded in 26 of the 35 patients (Figs. 2A, 2B, and 2C) without ACS by MDCT (specificity, 74%; 95% CI, 75-88%; negative predictive value, 100%; 95% CI, 87-100%).
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A subanalysis showed the improved specificity of 64-MDCT (60% vs 86% for 16- vs 64-MDCT, respectively). A summary of the overall accuracy, sensitivity, specificity with 95% CI, positive and negative predictive values, and diagnostic odds ratio for the presence of significant stenosis (> 50% luminal narrowing) in MDCT compared with the discharge diagnosis (ACS vs no ACS), and comparison between 16- and 64-MDCT are given in Table 2.
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In seven patients (17.5%) who underwent invasive coronary angiography, MDCT correctly detected the presence of stenosis in five patients and ruled out stenosis in two patients.
Projected Length of Hospital Stay in Patients Without Acute Coronary Syndrome and With Negative MDCT
In 26 patients, ACS was ruled out by standard clinical evaluation, and the
presence of significant stenosis was excluded by MDCT. The average length of
stay for standard clinical care was 30.5 ± 17.3 hours (range, 7.6-76.2
hours), compared with an average projected length of stay for an MDCT-based
strategy of 7.8 ± 3.1 hours (range, 4-11.4 hours) (p <
0.001). Thus, an MDCT-based triage strategy would have saved 598 hospital
hours overall.
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Although risk stratification schemes have been suggested for patients with acute chest pain on the basis of clinical presentation and risk factors to identify patients with low risk of ACS [4, 11], translation of these schemes into clinical decision-making has been difficult. This diagnostic dilemma is emphasized by the wide range (1-90%; mean, 30% ± 24%) of clinical pretest probabilities in our patient cohort as assessed by emergency department staff at the time of triage. In these patients, triage based on traditional risk stratification is ineffective.
We show that it is feasible to perform coronary MDCT in patients presenting with chest pain awaiting hospital admission. All patients underwent MDCT scanning without complications. We report an overall sensitivity of 100% and specificity of 74% to appropriately admit or discharge patients with suspected coronary ischemia, using the detection of significant coronary artery stenosis as a triage criterion. All five patients who were discharged from the hospital with a diagnosis of ACS were identified as having significant coronary stenoses by MDCT. In addition, no patient in whom MDCT excluded the presence of significant coronary stenoses (n = 26) developed ACS during index hospitalization, potentially reducing the number of unnecessary hospital admissions by nearly 70%. These data establish initial evidence that implementation of noninvasive coronary imaging in the emergency department could change existing paradigms for triage and care of patients with acute chest pain. Also, the study results show that noninvasive coronary imaging by MDCT improves early risk stratification in these patients. Whether this finding will result in change of patient care—that is, immediate discharge of patients with negative MDCT or earlier referral to invasive coronary angiography—cannot be definitely concluded from this study; however, the study justifies further evaluation in large-scale randomized clinical trials. This information may be particularly valuable for hospitals without a coronary angiography facility given the data that clearly support early invasive treatment strategies over noninvasive treatment [2].
We sought to determine whether MDCT could improve the clinical standard of risk stratification in patients with acute chest pain. Although the presence of a significant coronary stenosis is not equal to ACS, in most patients with unstable angina or NSTEMI (80-94%) significant coronary stenosis is detected on coronary angiography performed during the index hospitalization [27-29]. In addition, the detection of significant coronary stenosis is the most established and validated finding of coronary MDCT. One may argue that this method of risk stratification, which is based on significant coronary stenosis, is limited in several aspects. MDCT may fail to detect a minority of patients with acute chest pain and ECG changes that are suggestive of ACS but have normal or nonobstructive disease at angiography because of transient ischemia caused by vasospasm or thrombus, or who have endothelial dysfunction or microvascular disease [30, 31]. However, currently available methods of diagnostic testing, including stress testing or selective coronary angiography, are also unrevealing in these patients. Although stress MRI (adenosine) or phosphorus-31 MR spectroscopy may identify perfusion abnormalities in these patients [32, 33], these methods are not typically available or are used in the clinical setting of acute chest pain.
Noninvasive imaging of nonobstructive coronary atherosclerotic plaque with MDCT [34-36] permits the analysis of the presence, extent, morphology, and composition of coronary plaque. Larger studies are necessary to determine whether the assessment of plaque characteristics such as plaque surface morphology or remodeling index will provide further insight into the coronary pathophysiology underlying a patient's presentation with chest pain.
Because our equipment was upgraded during the study, we used two CT scanners, a 16-MDCT in the first 17 patients and a 64-MDCT in the subsequent 23 patients. Our data show that the overall image quality of coronary MDCT has significantly improved using 64-MDCT with better spatial and improved temporal resolution. Although image quality was limited in 35% of patients scanned with 16-MDCT, this fraction decreased to 7% in patients scanned with 64-MDCT. In contrast, image quality was excellent in 30% of patients scanned with 16-MDCT but increased to 58% of patients scanned with 64-MDCT. Thus, our results are in accord with a growing body of literature showing that the number of segments that cannot be evaluated for stenosis because of image artifacts has significantly decreased with the introduction of 64-MDCT [22, 23]. A subanalysis of our data shows that this increased the confidence of MDCT interpreters to rule out the presence of stenosis resulting in an increased specificity of the test (specificity, 60%; [95% CI, 28-92%] vs 85% [95% CI, 68-102%] for 16-versus 64-MDCT, respectively). This is further emphasized by the improved diagnostic odds ratios between the two subgroups (149 vs 561 for 16- vs 64-MDCT, respectively).
However, our results also indicate that the usefulness of MDCT may be limited in patients with prior stent placement, bypass procedures, or severe calcification. Among the seven patients in whom a significant stenosis could not be excluded by MDCT, none had excellent image quality, two patients had previous bypass surgery, three patients had stents, and two patients had severe calcifications. Although recent data suggest good diagnostic accuracy for the detection of stent and bypass patency, this may be currently limited to large stents (> 3.0 mm in diameter) and venous bypass grafts. Image artifacts because of metallic clips or small stents may prevent confident exclusion of coronary stenosis in most of these patients. Large studies are warranted to better define patient groups in whom MDCT may not be useful in the triage of patients with acute chest pain to prevent unnecessary radiation exposure.
In this study, we consistently used tube current modulation, a technique that restricts the full tube current to the diastolic phase of the cardiac cycle [37] and reduces the radiation exposure from cardiac MDCT by up to 50% to 6-11 mSv [38]. Although this may result in suboptimal image quality in patients with premature ventricular contractions or high heart rates, we believe that this reduction of radiation exposure is a prerequisite for the potential implementation of cardiac MDCT in the workup of patients with acute chest pain.
Finally, our data provide initial evidence that an MDCT-based strategy may decrease the cost of standard clinical care by significantly reducing the length of hospital stay. Using MDCT-based detection of stenosis as a single criterion for the presence of ACS; only 14 of 40 patients would have been admitted to the hospital based on the MDCT findings without missing a patient with ACS, and unnecessary admissions would have been avoided in 26 patients (65%). The 26 patients in whom ACS was ruled out both by standard clinical care and MDCT during index hospitalization spent an average of 30.5 ± 17.3 hours (range, 7.6-76.2 hours) in the hospital. The average length of stay for an MDCT-based strategy would have been 7.8 ± 3.1 hours (4-11.4 hours). A crude estimate indicates the potential of an MDCT-based strategy to save a significant amount of hospital time (on average 22.7 ± 19.4 hours per patient or 598 hospital hours overall). These data, of course, cannot predict whether an MDCT-based strategy would be cost-effective, but they do justify conducting large studies to construct and verify decision models that will provide critical information necessary to plan future economic evaluations as part of randomized controlled trials comparing different diagnostic strategies with and without the use of MDCT.
Study Limitations
In the present study, we investigated a relatively small patient cohort
with a severely limited window of enrollment. However, all eligible patients
who presented to the emergency department between 9 am and 5 pm on enrollment
days were included in the study. Because the cardiac MDCT scanner is not
staffed on nights and weekends, patients presenting during these time frames
were not included in the study. Nevertheless, age, sex, race distribution, and
the fraction of patients with previous history of CAD are similar to those
patients in larger clinical ACS trails
[39], suggesting that the
selection bias is likely to be very small. In addition, the time to
presentation to the emergency department after onset of chest pain in our
population (mean, 3.0 ± 2.2 hours) is consistent with previous
observations in U.S. metropolitan areas
[40]. We do not report
follow-up data on our patient cohort. However, event rates in patients at low
risk who were discharged without the diagnosis of ACS during index
hospitalization were below 1%
[10]. We did not observe a
significant difference in the clinical pretest probability of ACS among
patients who were and were not eventually diagnosed as having ACS. A more
uniform scale to assess probability of ACS than our subjective assessment may
perform better; moreover, we may not have enough power to detect differences
in this study. However, despite these limitations, clinical triage without any
further testing is likely to remain problematic.
In conclusion, this pilot study shows that it is feasible to perform coronary MDCT in acutely ill patients. Moreover, our data suggest that MDCT-based detection of significant coronary stenoses has tremendous potential to decrease the number of unnecessary hospital admissions, without reducing appropriate admissions, in patients with chest pain who have nondiagnostic ECG results and normal cardiac enzymes.
Large studies are necessary to confirm these results and to determine whether MDCT is cost-effective in this setting. Furthermore, additional MDCT-based triage criteria such as the presence, composition, and morphology of coronary atherosclerotic plaque need to be investigated.
Acknowledgments
We gratefully acknowledge the dedicated support in patient enrollment by
the team of residents, attending physicians, nurses, and administrative staff
in the department of emergency medicine at our institution. Furthermore, we
acknowledge the essential roles of Uwe Siebert, Javed Butler, Koen Nieman,
David Brown, Blair Parry, and Thomas J. Brady.
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