Summary
Background
Coronary computed tomography (CCT) detects coronary obstruction with high sensitivity and might be useful for diagnosis of angina pectoris.
Aim
In this pilot study, we sought to prospectively evaluate the performance of CCT as initial work up and determine the significance of this strategy according to the pretest likelihood of having coronary artery disease (CAD).
Methods
One hundred and eighty patients with chest discomfort and suspected angina were prospectively referred for CCT with a 64-slice CT scan. Invasive coronary angiography (ICA) was performed on the basis of CCT findings (stenosis > 50%). Patients were classified into tertiles according to estimated pretest probability of obstructive CAD using the Duke Clinical Score (low, intermediate and high). Strategy failure was defined as unnecessary ICA or major adverse cardiac event (MACE) within 6 months in patients without significant stenosis by CCT.
Results
Pretest probability for CAD was 53 ± 29%. Significant stenosis was detected by CCT in 51 patients; 47 (26%) underwent ICA. Sixteen strategy failures were reported: 15 patients (10%) were referred for ICA that did not confirm significant coronary stenosis and one MACE occurred in a patient without significant stenosis by CCT. Strategy failures were 8% in low-probability, 1.7% in intermediate-probability and 15% in high-probability patients ( P = 0.03).
Conclusions
CCT as an initial step for angina diagnosis is most effective in patients with an intermediate probability of CAD. In patients with low or high likelihood, it is associated with a high rate of unnecessary ICA but not with adverse events.
Résumé
État des lieux
Le coroscanner détecte les obstructions coronaires avec une grande sensibilité et pourrait être utile au diagnostic le l’angor stable.
Objectifs
Dans cette étude pilote, nous avons prospectivement évalué la performance du coroscanner comme examen initial et déterminé la pertinence de cette stratégie en fonction de la probabilité de la maladie coronaire.
Méthodes
Cent quatre-vingt patients avec douleur thoracique suspecte d’angor ont été évalués par coroscanner multicoupes. Une coronarographie n’était indiquée que sur la base du coroscanner (sténose > 50 %). Les patients ont été classés en fonction de leur probabilité initiale de maladie coronaire en utilisant le score de Duke (faible, intermédiaire, élevé). Un échec de la stratégie était défini comme réaliser une coronarographie blanche (absence de sténose significative) ou la présence d’un événement cardiaque à six mois chez les patients à coroscanner normal.
Résultats
La probabilité initiale de maladie coronaire était de 53 ± 29 %. Une sténose significative a été détectée par scanner chez 51 patients et 47 (26 %) ont été coronarographiés. Quinze patients (10 %) ont eu une coronarographie blanche et un patient est décédé alors qu’il n’avait pas de sténose au coroscanner. Les échecs de la stratégie étaient de 8, 1,7 et 17 % dans les groupes respectifs de probabilité de maladie coronaire faible, intermédiaire et élevée ( p = 0,015).
Conclusions
Le coroscanner comme étape initiale du diagnostic de l’angor stable est plus pertinent chez les patients à risque intermédiaire de maladie coronaire. Chez les autres patients, une telle stratégie est associée à un taux élevé de coronarographie blanche.
Background
Current guiding principles for angina pectoris recommend functional testing in order to establish the presence of myocardial ischaemia . Coronary angiograms confirm obstructive coronary artery disease (CAD) and are performed on the basis of initial functional tests, especially stress echo and nuclear imaging. Coronary computed tomography (CCT) is a rapidly developing technique that allows reliable evaluation of the coronary arteries compared with invasive coronary angiography (ICA) . CCT has shown high sensitivity for detecting obstructive coronary disease in a non-invasive manner and subsequently has been introduced for diagnosis of angina pectoris . Although CCT does not evaluate the functional impact of CAD, its overall performance (availability and reliability) appears promising and might play a role in angina diagnosis. The adequate value of CCT as initial work up for chronic angina has not been established. From retrospective analysis, CCT usefulness appears to be dependent on the pretest probability of having CAD and might be most advantageous in subsets of patients, especially those with an intermediate risk . In this pilot study, we prospectively included patients with suspected angina (non-acute coronary syndrome), evaluated the performance of CCT as initial work up, and determined the impact of such a strategy on further investigations and clinical events according to the pretest likelihood of having CAD.
Methods
Patients
Patients presenting with typical or atypical angina pectoris from the outpatient setting were referred for a CT scan and prospectively included in the study. A dedicated information sheet and database were used for data collection. Typical angina was defined as having three characteristics: substernal discomfort that is precipitated by physical exertion or emotion and relieved with rest or sublingual nitroglycerine. Atypical angina pectoris was defined as having two of the three definition characteristics. Inclusion criteria were: patients referred for a CT scan as an initial work-up test; and patients with a preceding submaximal stress test during a 6-month period (February to July 2009).
Exclusion criteria were: non-sinusal cardiac rhythm; abnormal electrocardiogram (ECG) at rest, suggestive of CAD (Q-wave, ST-segment depression and left bundle block); previous history of angina, myocardial infarction, percutaneous coronary intervention, coronary artery bypass surgery or impaired renal function (serum creatinine > 120 μmol/L); and known allergy to iodinated contrast material. The estimated pretest probability for obstructive CAD was estimated using the Duke Clinical Score, which includes type of chest discomfort, age, sex and traditional risk factors . Patients were categorized into low-, intermediate- or high-probability groups according to tertiles of estimated pretest likelihood of having significant CAD. Conventional coronary angiography was performed within 1 month after CT and was based on CT findings (suspected stenosis > 50%). The protocol was reviewed and accepted by the ethics committee of our Cardiology Board.
Scan protocol
All patients with a heart rate greater than 70 beats/min received intravenous beta-blockers (atenolol 5–15 mg) before CT examination; target heart rate was less than 60 beats/min. All scans were performed with a 64-slice CT scanner (Lightspeed VCT; GE Healthcare, Chalfont St. Giles, UK) that features a gantry rotation time of 350 ms, a temporal resolution of 175 ms and a spatial resolution of 0.54 mm 3 . Tube voltage was 120 kV (100 kV for patients weighing < 70 kg) and X-ray tube current was modulated on the ECG (250–650 mA). CT was acquired in a breath-hold and was ECG gated. Rotation speed and pitch were adjusted to the acquisition protocols and to the heart rate. Calcium scoring was not performed. A bolus of contrast media (Ioxaglate 320 mg I/mL, Guerbet) was infused into an antebrachial vein with the use of a dual-barrel injector (70 cc of contrast medium at 5 cc/s washed out by 30 cc of isotonic solution at 3.5 cc/s). CT data were analysed by the use of an offline Advantage Workstation (GE Healthcare) using prior interactive interpretation of axial images followed by (curved) multiplanar reconstruction. Phases from 0–90%, every 10%, were systematically reconstructed to allow for imaging of coronary arteries. Segments were scored as positive for significant CAD if there was a greater or equal to 50% diameter reduction of the lumen (in a vessel with a reference diameter greater or equal to 2 mm) by visual assessment. Three experienced observers (> 500 CT coronary angiograms) who were blinded to previous medical history and symptoms participated in the study (one interpreter per patient). Optimal quality CT scan was defined as lumen visual assessment available in all coronary arteries greater than 2 mm in diameter. For patients with non-optimal quality CT (including heavy calcification without lumen assessment), ICA was suggested.
Angiographic analysis
Baseline quantitative angiography was performed using the contrast-filled injection catheter for image calibration. Cine angiographic stenosis was defined as stenosis greater than 50%. Quantitative coronary angiographic analysis was performed using the Integris H5000C software (Philips, Amsterdam, The Netherlands). Myocardial revascularization was recommended on the basis of current guidelines on the management of stable angina, in view of symptoms, functional tests, medical history and ICA findings .
Outcome
Clinical follow-up was performed at 6 months by phone call and/or physician visit. A major cardiac event was defined as death (all-cause mortality), Q-wave and non-Q-wave myocardial infarction (total creatinine kinase elevation greater or eqaul to three times normal and/or new pathological Q-waves in greater or equal to two contiguous leads) or ICA. Strategy failure was defined as either performing an ICA that showed no significant stenosis in a patient with suspected stenosis by CCT (unnecessary ICA) or a major adverse cardiac event (MACE) in a patient without suspected stenosis by CCT (false negative CCT).
Statistics
Continuous variables are expressed as means ± standard deviations. Categorical data are expressed as percentages. Chi 2 statistics and Fisher’s exact test were used to compare continuous variables and categorical values, respectively. A p value less than 0.05 was considered statistically significant. Statview 5.0 software (SAS Institute Inc., Cary, NC, USA) and the VASSAR web calculator ( www.vassar.edu ) were used to perform the analysis.
Results
Baseline characteristics of the population are presented in Table 1 . Pretest probability of CAD was 53 ± 29%. According to tertiles, patients were classified as low probability (range 2–33%), intermediate probability (34–69%) and high probability (70–100%). Only 45 patients (25%) had a previous submaximal stress test; 135 had no previous test before CCT. CCT was defined as optimal in 163 patients (91%). Radiation dose was 1200 ± 355 mGy.cm (20.4 ± 6.0 mSv). No significant side effect besides nausea was reported and all patients were discharged immediately after CT. Reasons for non-optimal CT were heart rate greater than 80 beats/min despite atenolol ( n = 8), heavy coronary calcifications ( n = 5), extrasystoles during acquisition ( n = 3) and high corpulence ( n = 1). CT identified 51 patients with suspected coronary stenosis greater than 50% ( Table 2 ). Four patients did not undergo ICA: two patients declined; and two patients were asymptomatic with a negative stress test after medical treatment initiation and were not referred for ICA in view of CT findings (one-vessel disease/distal left anterior descending in one patient; two-vessel disease/diagonal and obtuse marginal in one patient). ICA was performed in 47 patients, and significant stenosis (> 50%) was confirmed in 32 patients ( Table 3 ). The rate of ICA without significant coronary stenosis was 83% in low-probability patients, 30% in high-probability patients and 9% in intermediate-probability patients ( p = 0.007). Table 4 details explanations for discrepancies between positive CCT and non-obstructive coronary artery disease by ICA. Revascularization was performed in 29 patients, all by percutaneous coronary angioplasty, including 17 patients with typical angina pectoris and 12 patients with atypical chest pain and coronary stenosis greater than 70% by ICA. Ultimately, eight patients had a stress test (one ischaemia on nuclear test; seven tests were submaximal).
