The characteristics of the chest pain unit in our hospital have been previously described.3 The unit applies a diagnostic protocol to assess patients with nontraumatic chest pain, according to the guidelines of the Spanish Society of Cardiology.15

This study consecutively included patients without a history of cardiac disease who attended the emergency department with typical or atypical angina during working hours between Tuesday and Friday in 2008. Only patients with a negative troponin level within 6h of pain onset and no electrocardiographic signs of ischemia were included. These patients are typically considered candidates for exercise stress testing. The study also included patients older than 35 years who had a pretest probability of CAD greater than 10% according to the nomograms developed by Pryor et al.16Figure 1 shows the patient selection flowchart. Exclusion criteria were contraindications to MDCT, such as irregular heart rhythm, kidney failure (creatinine > 1.3mg/dL), anaphylactic reaction to iodine contrast, contraindications to beta blockers, and contraindications to exercise testing.

Figure 1.

Patient selection flowchart. ACS, acute coronary syndrome; CAD, coronary artery disease; CPU, chest pain unit; ECG, electrocardiogram; NSTEACS, acute coronary syndrome without ST segment elevation; STEACS, acute coronary syndrome with ST segment elevation.

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Eligible patients underwent MDCT and exercise echocardiography. Exercise echocardiography was performed first in 90% of patients to avoid the negative chronotropic effect of the beta blockers needed for MDCT. Patients with negative results were discharged except when the consultant cardiologist decided to admit the patient for catheterization due to the character and persistence of chest pain. A presumptive diagnosis of ACS was established in patients with a positive exercise echocardiogram and in patients with positive MDCT, defined as the presence of at least 1 coronary lesion with stenosis ≥ 50% or an Agatston score ≥ 400. All these patients were included in the study and underwent treatment. During admission, all included patients underwent cardiac catheterization except for 3 patients who were excluded by the attending physician. Patients with inconclusive results on MDCT or exercise echocardiography were considered to have positive results for the purposes of statistical analysis. The study was approved by the hospital's ethics committee and all patients signed their informed consent.

A 64-slice scanner (Sensation 64, Siemens Medical Solutions; Forchheim, Germany) was used. Patients with a heart rate > 65 were treated with beta blockers. Firstly, the Agatston calcium score was calculated by acquiring low-resolution images without contrast at a slice thickness of 3mm. Angiography was not performed in patients with chest pain and a documented Agatston score > 400 due to the difficulty of interpreting the coronary lumen and the high prevalence of myocardial ischemia.17 The remaining patients were administered 400μg of sublingual nitroglycerin. After administration of a bolus of 80 (10) mL of contrast (Iomeron 400®, Rovi), angiography was performed at a trigger threshold of 120 HU in the ascending aorta. Acquisition parameters were as follows: collimation, 64mm×0.6 mm; rotation time, 370ms (equivalent to a time resolution of 185ms); tube voltage, 120kV; and effective tube current, 550mA-850mA. Dose-modulation techniques were used and image acquisition was optimized between 30% and 70% of the RR interval.

Subsequently, cardiac volume was reconstructed at a slice thickness of 0.75mm and with an increase of 0.4mm between slices at 60%, 65%, 70%, and 75% of the RR interval. Images were interpreted using the Circulation® software package (Siemens; Erlangen, Germany), which allows volumetric and multiplanar reconstructions and maximum-intensity projections.

Each study was jointly evaluated by an experienced radiologist and an experienced cardiologist, who together determined the presence of luminal area stenosis<50% or ≥ 50%, nonassessable segments, and the cause of nonassessment (motion artifact or severe calcification). Differences of opinion were resolved by a third observer. The mean interpretation time was 18(8) min.

Patients underwent symptom-limited treadmill exercise testing using the Bruce protocol under electrocardiographic monitoring using a Vivid 7 ultrasound system (General Electric) equipped with an exercise protocol. Images were acquired at baseline, immediately after the test, and during recuperation in parasternal long-axis and parasternal short-axis views and in 2-chamber and 4-chamber views. An echo enhancer (Sonovue®, Rovi, Madrid, Spain) was only used to improve endocardial border delineation in the case of a suboptimal acoustic window. The studies were evaluated by an experienced echocardiologist, without access to the results of other tests, according to the 17-segment model proposed by the American Heart Association. The myocardial wall motion study was considered positive in the presence of segmental wall-motion abnormalities at baseline or when induced by exercise in at least 2 adjacent segments.18

Due to the exploratory nature of this study, the overall result of exercise echocardiography was considered positive when at least of the 3 components (clinical suspicion, electrocardiographic changes, and wall-motion abnormalities) was positive. The study was considered inconclusive when the wall-motion study was not conclusive, a metabolic equivalents score of 6 was not reached, or 85% of the predicted maximum heart rate was not achieved.

Acute coronary syndrome was confirmed by the presence of typical or atypical angina plus one of the following characteristics: presence of coronary lesions with > 70% stenosis determined by cardiac catheterization; ischemia induced in a diagnostic test other than exercise echocardiography; or the presence of cardiac death, acute myocardial infarction, or need for revascularization at 6-month follow-up.18

Continuous variables are described as mean (standard deviation). Between-groups comparisons were performed using the Student t test for continuous variables and the chi-square test for discrete variables using Yates correction as needed. A P value < .05 was used as a cutoff for statistical significance.18

In 40 patients (58%), MDCT was normal or showed no significant lesions (stenosis<50%). Multidetector computed tomography was positive in 27 (39.1%) patients: 22 had > 50% stenosis and 5 had an Agatston score > 400. In 2 patients (2.9%) ≥ 1 proximal or middle coronary segment could not be assessed due to motion artifacts. Thus, based on MDCT, a presumptive diagnosis of ACS was established in 29 (42%) patients. All the patients with stenosis ≥ 50% on MDCT had an Agatston score > 0. In addition, 4 of the 5 patients with an Agatston score > 400 had ACS with coronary stenosis > 70% on cardiac catheterization. One patient with a calcium score = 0 and a coronary segment that could not be assessed had a severe lesion in this segment on cardiac catheterization.

Exercise echocardiography was negative in 49 (71%) patients, positive in 17 (24.6%), but inconclusive in 3 (4.3%) due to poor image quality or the patient achieving 85% of the predicted maximum heart rate. Table 2 shows the characteristics of exercise echocardiography. Based on the results of exercise echocardiography, ACS was suspected in 20 (29%) patients.

Figure 2 shows the relationship between the diagnostic tests and the diagnosis of ACS. Acute coronary syndrome was correctly ruled out in all patients with a normal MDCT. The exercise echocardiogram was positive in 1 of these patients and inconclusive in another. However, of the 29 patients with positive or inconclusive MDCT, exercise echocardiography was positive in 16 patients (55.2%), negative in 11 (37.9%), and inconclusive in 2. A final diagnosis of ACS was confirmed in 58.6% of suspected cases of ACS by MDCT and in 66.7% of suspected cases of ACS by exercise echocardiography (P=.56). Acute coronary syndrome was confirmed in 14 of the 17 patients with positive exercise echocardiography but in none of the 3 patients with inconclusive findings. Exercise echocardiography was negative in 3 patients with ACS. Figures 3 and 4 show 2 examples of concordance between negative MDCT and positive cardiac catheterization and exercise echocardiography.

Figure 2.

Results of multidetector computed tomography and exercise Echocardiogram for acute coronary syndrome. ACS, acute coronary syndrome; +, positive; –, negative; Echo, echocardiography; MDCT, multidetector computed tomography; NC, not conclusive.

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Figure 3.

Multidetector computed tomography. Curved multiplanar reconstructions of the right coronary artery (A), left anterior descending artery (B) and circumflex artery (C) showing significant coronary lesions in the 3 vessels confirmed by cardiac catheterization (lower line) in a patient with negative exercise echocardiogram.

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Figure 4.

Curved multiplanar reconstructions (A and B) and volumetric reconstructions (C) in a patient with mixed lesion with severe stenosis in the left anterior descending artery confirmed by cardiac catheterization (D). End-systolic frame on exercise echocardiography shows a dyskinetic area at the apex (arrows) inducible with exercise (E), which is not present at rest (F).

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Using a ≥ 50% stenosis cutoff value, the sensitivity of MDCT was greater than that of exercise echocardiography in detecting ACS in this population (100% vs 82.3%; P>.05), but its specificity was lower (76.9% vs 88.4%: P>.05) (Table 3). Notably, when the stenosis cutoff value was raised to ≥ 70% in the retrospective analysis, the specificity of MDCT increased to that of exercise echocardiography (88.4% with both techniques) while maintaining 100% sensitivity. Separate analysis of the 3 exercise echocardiography components showed the low sensitivity but high specificity of clinical suspicion and inducible ventricular wall-motion abnormalities in detecting ACS. The assessment of electrocardiographic abnormalities alone during exercise showed acceptable values of sensitivity and specificity (82.3% and 80.8%, respectively), but a low positive predictive value (58.3%). The diagnostic accuracy of exercise echocardiography was slightly higher than that of MDCT using a 50% stenosis cutoff value (Table 3).

Cardiac catheterization was performed at admission in 29 patients. In 26 of these patients, the procedure was performed because of positive results of either exercise echocardiography or MDCT, or both. The attending clinical cardiologist also ordered cardiac catheterization procedures in 3 patients with normal test results who had recurrent chest pain, and rejected the use of cardiac catheterization in 3 patients with lesions ≥ 50% on MDCT and normal exercise echocardiography.

During admission, 12 patients underwent revascularization. All 12 patients had positive MDCT, 11 had positive exercise echocardiography, and 1 had negative exercise echocardiography. One sudden death was recorded at 5 months in a patient with a lesion > 70% on MDCT, negative results on exercise echocardiography, and 60% stenosis on cardiac catheterization. In addition, 2 patients with an initial diagnosis of ACS underwent urgent revascularization, 1 of whom initially received medical treatment. At 4-year follow-up, the other patient underwent angioplasty for a severe (50%) lesion on initial MDCT. The lesion was not responsible for the initial ACS.

Our study has important limitations. Firstly, the patient sample was small and catheterization was not performed in all patients. Therefore, the sensitivity and specificity values reported should be taken with caution. Furthermore, as shown in Figure 1, the population was highly selected because the sample selection period was very limited and patients with a known history of heart disease and contraindications to either of the 2 tests were excluded. Both these factors would have caused selection bias. This initial pilot study was designed to highlight differences in the information provided by MDCT and exercise echocardiography. Therefore, larger randomized studies are needed to compare the safety and efficiency of both techniques. Furthermore, the results of both the MDCT and exercise echocardiogram were communicated to the medical team, which introduced a referral bias was that clearly influenced the diagnosis of ACS, since both techniques were used to assess the need for cardiac catheterization. Finally, no images were acquired during peak exercise, although these images have been shown to improve the diagnostic sensitivity of the technique.25