Summary
Background
Coronary angiography (CA), an invasive and expensive procedure, is still recommended in most patients referred for elective valve surgery. Multislice computed tomography (MSCT) is a promising alternative technique to rule out significant coronary artery lesions.
Aim
To evaluate MSCT in detecting significant coronary artery lesions in patients referred for elective valve surgery.
Methods
Between August 2007 and December 2010, patients referred for elective valve surgery were identified prospectively and underwent 64-slice MSCT and CA. We compared significant coronary stenoses, defined as a reduction of luminal diameter ≥ 50%, to establish the diagnostic accuracy of MSCT. All coronary segments were analysed and uninterpretable lesions were scored positive.
Results
Forty-eight patients were included (62.5% male; mean age 65 ± 12 years), the majority had aortic insufficiency (37.7%) or aortic stenosis (32.0%). The prevalence of significant coronary artery stenoses was 27.1%. The sensitivity, specificity, positive and negative predictive values of MSCT were 77%, 89%, 71% and 91%, respectively, in a patient-based analysis; 82%, 86%, 64% and 94% in a revascularization-based analysis; 67%, 94%, 52% and 97% in a vessel-based analysis; and 65%, 98%, 52% and 99% in a segment-based analysis. Overall, CA could have been avoided in 65% of patients.
Conclusion
In patients referred for elective valve surgery, MSCT had a high diagnostic accuracy to rule out significant coronary stenoses. However, larger multicenter studies in an unselected population of patients are needed to determine its place within the range of diagnostic tool in the preoperative assessment of valvular heart disease.
Résumé
Contexte
La coronarographie est un examen coûteux et invasif, toujours recommandé chez les patients programmés pour une chirurgie valvulaire. La tomodensitométrie multicoupe (TDMC) apparaît comme une alternative prometteuse pour éliminer les sténoses coronaires significatives.
Objectif
Pour évaluer la précision diagnostique de la TDMC dans l’évaluation de la maladie coronaire avant la chirurgie valvulaire cardiaque.
Méthodes
Entre août 2007 et décembre 2010, les patients adressés pour une chirurgie de remplacement valvulaire ont été inclus pour effectuer de manière prospective une TDMC et une coronarographie. On a comparé les sténoses coronaires significatives, définies par la réduction du diamètre luminal supérieur ou égal à 50 %, pour établir la précision diagnostique de la TMDC. Les lésions ininterprétables ont été considérées positives.
Résultats
Quarante-huit patients ont été inclus (62,5 % de sexe masculin ; âge moyen de 65 ± 12 ans), la majorité avait une insuffisance aortique (37,7 %) ou un rétrécissement aortique (32,0 %). La prévalence de la maladie coronaire était de 27,1 %. La sensibilité, spécificité, les valeurs prédictives positives et négatives de la TDMC étaient respectivement de 77 %, 89 %, 71 % et 91 % en analyse par patient ; 82 %, 86 %, 64 % et 94 % en analyse par revascularisation ; 67 %, 94 %, 52 % et 97 % en analyse par artère ; et 65 %, 98 %, 52 % et 99 % en analyse par segment. La coronarographie aurait pu être évitée chez 64,5 % des patients.
Conclusion
Chez les patients programmés pour une chirurgie valvulaire, la TDMC bénéficie d’une bonne précision diagnostique pour exclure les sténoses coronaires significatives. Toutefois, de larges études multicentriques portant sur une population non sélectionnée de patients, sont nécessaires pour déterminer sa place au sein de l’arsenal diagnostique dans l’évaluation préopératoire de la maladie valvulaire cardiaque.
Background
Various studies have shown that combined bypass and valve surgery of significant coronary artery disease (CAD) reduces early and late mortality . Coronary angiography (CA) is the gold standard for diagnosing CAD, and is recommended in patients scheduled for valve surgery . However, CA is an invasive and expensive procedure, with a small (0.1–0.2%) risk of major complications such as death, myocardial infarction and stroke. A primary non-invasive technique as an alternative to CA to improve preoperative risk stratification in patients referred for valve surgery is therefore highly desirable.
Multislice computed tomography (MSCT) has a good negative predictive value for ruling out CAD in patients with intermediate pre-test probability . However, few studies have examined coronary artery assessment by MSCT in patients scheduled for elective valve surgery .
We conducted a prospective study to evaluate the diagnostic accuracy of 64-slice MSCT for the detection of significant artery lesions in patients referred for elective valve surgery.
Methods
Study population
Consecutive patients scheduled for valve surgery were screened prospectively from August 2007 to December 2010. As a previous study had shown good results for MSCT in patients with aortic stenosis , we initially excluded patients with aortic stenosis in order to explore the diagnostic accuracy of MSCT in patients with other valve diseases. However, owing to low patient numbers, from mid-2008 we also included patients with aortic stenosis. Exclusion criteria included: atrial fibrillation, previous coronary artery bypass graft (CABG), an unstable haemodynamic state, acute renal insufficiency, previous allergic reaction to iodine contrast media, pregnancy and lactation. The study was approved by the French Society of Cardiology; and all patients signed an informed consent form.
Patient preparation
MSCT and CA were performed in all patients within 3 weeks of each other. All patients with baseline heart rate greater than 65 beats per minute received 5 to 10 mg of intravenous atenolol 10 min before the examination.
MSCT protocol
All scans were performed using a 64-slice MSCT (Philips, Brilliance 64 CT scanner, Eindhoven, Holland). The scan protocol included slices of the aortic artery for 10 patients for whom a transcatheter aortic valve implantation was discussed. Thus, the median radiation exposure for MSCT with this scan protocol was calculated as 16 mSv, although prospective X-ray tube modulation was used. A standardized examination protocol, with 64 × 0.625 mm collimation, pitch of 0.2 and a tube rotation time of 400 ms, was used. The typical tube voltage was 120 kV, with a tube current of 600–900 mAs, depending on patient size, body mass index and thoracic diameters in the scan area. A mean of 114 ± 23 mL of iodine contrast agent (400 mgI/mL, Iomeron, Bracco, Milan, Italy) was injected continuously at a rate of 8 mL/s to explore solely the coronary arteries. A bolus tracking technique with automated detection of peak enhancement in the ascending aorta was used to time the scan. Coronary assessment was done during a single breath-hold.
Radiologists used multiplanar reformations and three-dimensional reconstructions to detect significant coronary stenoses, defined as a mean lumen reduction greater than 50%. They used the 17-segment American Heart Association (AHA) classification to describe coronary lesions and they were blinded to clinical data. All vessels were included in the analysis, and any that were uninterpretable were scored as significant coronary stenoses.
Coronary angiography
Coronary angiograms were analysed by one experienced cardiologist [H.G.], who was unaware of the MSCT results, using a modified 17-segment AHA classification . All coronary segments were visually assessed. Those with significant narrowing were quantified by a validated QCA algorithm (CAAS, Pie Medical, Maastricht, The Netherlands). They were evaluated in two orthogonal views, and were classified as significant if the mean lumen diameter reduction was greater than 50%.
Statistical methods
The diagnostic accuracy of MSCT was compared with that of CA as the reference standard for the detection of significant stenosis in the coronary arteries. All diagnostic accuracy parameters, sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios are given with their corresponding 95% confidence intervals (CIs). Interobserver agreement was assessed by Cohen Kappa statistics, and was performed for four analyses: by patient, by revascularization, by vessel and by segment.
Continuous variables are reported as medians and interquartile ranges (IQRs), and categorical variables as numbers and percentages. Comparisons between patients with and without aortic stenosis were performed using Student’s t test for independent samples for continuous variables, and a χ 2 test or Fisher’s exact test when appropriate for categorical variables. A P value less than 0.05 was considered significant. All analyses used XLSTAT Version 2011.2.08 (Addinsoft Inc., New York, NY, USA).
Results
Patient characteristics
Of 66 consecutive patients scheduled for valve surgery during August 2007 to December 2010, 18 were excluded due to limited patient and time availability to perform MSCT before surgery ( n = 11), withdrawal of written consent ( n = 5), acute renal insufficiency ( n = 1) and previous allergic reaction to iodine contrast media ( n = 1). Demographics of the remaining 48 patients are shown in Table 1 . Most patients had aortic insufficiency (37.7%) or aortic stenosis (32.1%); five patients had a double valvular disease. Approximately half of the patients were overweight, had hypertension, were (ex)-smokers, and had a left ventricular ejection fraction greater than 56% ( Table 1 ). The prevalence of CAD was 27.1%, mainly one-vessel disease (16.7%) ( Table 1 ).
| All patients ( n = 48) | |
|---|---|
| Men | 30 (62.5) |
| Age (years) | 63 (55–74) |
| Valvular heart disease a | |
| Aortic insufficiency | 20 (37.7) |
| Aortic stenosis | 17 (32.1) |
| Mitral regurgitation | 11 (20.7) |
| Mitral stenosis | 5 (9.4) |
| Reoperation | 2 (4.1) |
| Creatinine clearance (mL/kg/min) | 55 (45–66) |
| Risk factors | |
| Hypertension b | 26 (54.2) |
| Hypercholesterolaemia c | 20 (41.7) |
| Smoker | 7 (14.6) |
| Ex-smoker | 21 (43.8) |
| Family history of CAD | 13 (27.1) |
| BMI ≥ 25 kg/m 2 | 25 (52.1) |
| Diabetes mellitus | 4 (8.3) |
| Previous myocardial infarction | 1 (2.1) |
| Prior percutaneous coronary intervention | 9 (18.8) |
| Left ventricular ejection fraction (%) | 56 (47–65) |
| Distribution of disease by CA | |
| None | 35 (72.9) |
| 1 vessel | 8 (16.7) |
| 2 vessels | 2 (4.2) |
| 3 vessels | 3 (6.3) |
| MSCT dose length product (mGy cm) | 1190 (1032–1791) |
| MSCT contrast agent (mL) | 120 (95–125) |
| CA dose length product (mGy cm) | 416 (267–675) |
| Baseline treatment (%) d | |
| Beta-blocker | 13 (33.3) |
| Diuretic | 14 (35.9) |
a Patients could have more than one type of disease.
b Blood pressure ≥ 140/90 mmHg or treatment for hypertension.
c Total cholesterol ≥ 180 mg/dL or treatment for hypercholesterolaemia.
Patient-based analysis
MSCT correctly excluded CAD in 31 patients, with a specificity of 89% ( Table 2 ). Four patients classified as having significant coronary lesions had the severity of stenoses overestimated. MSCT correctly identified significant coronary lesions in 10 of 13 patients, resulting in a sensitivity of 77%. The diagnostic accuracy of a normal MSCT to detect patients without significant stenosis was 91%. The agreement on the presence of significant coronary lesions between the MSCT and CA was good (К value 0.64).
| Analysis by | Prevalence (%) | n | TP ( n ) | TN ( n ) | FP ( n ) | FN ( n ) | Kappa | Sensitivity a | Specificity a | PPV a | NPV a | +LR b | –LR b |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Patient | 27.1 | 48 | 10 | 31 | 4 | 3 | 0.64 | 77 (49–92) | 89 (73–96) | 71 (47–95) | 91 (81–100) | 6.7 (2.5–17.7) | 0.2 (0.1–0.7) |
| Revascularization c | 22.9 | 48 | 9 | 32 | 5 | 2 | 0.62 | 82 (51–95) | 86 (71–94) | 64 (40–90) | 94 (86–100) | 6 (2.5–14) | 0.2 (0–0.7) |
| Valvular heart disease | |||||||||||||
| AS | 58.8 | 17 | 8 | 6 | 1 | 2 | 0.64 | 80 (47–95) | 86 (46–100) | 89 (68–100) | 75 (45–100) | 5.6 (0.9–35) | 0.2 (0–0.8) |
| AI | 5.0 | 20 | 1 | 17 | 2 | 0 | 0.46 | 100 (17–100) | 89 (67–98) | 33 (0–86) | 100 (100–100) | 9.5 (2.5–35) | 0 |
| MS | 0 | 5 | 0 | 5 | 0 | 0 | – | – | 100 (50–100) | – | 100 (100–100) | – | – |
| MR | 18.2 | 11 | 1 | 8 | 1 | 1 | 0.40 | 50 (10–90) | 89 (54–100) | 50 (0–100) | 89 (60–100) | 4.5 (0.4–45) | 0.5 (0.1–2) |
| Coronary arteries | 9.4 | 192 | 12 | 163 | 11 | 6 | 0.54 | 67 (41–86) | 94 (89–96) | 52 (31–72) | 97 (92–98) | 10.6 (5.4–20) | 0.3 (0.2–0.7) |
| LM | 0 | 48 | 0 | 47 | 1 | 0 | – | – | 98 (89–100) | – | 100 (100–100) | – | – |
| LAD | 14.6 | 48 | 6 | 37 | 4 | 1 | 0.64 | 85 (46–99) | 90 (76–96) | 60 (30–90) | 97 (92–100) | 8.3 (3.3–23) | 0.1 (0–0.9) |
| Cx | 10.4 | 48 | 2 | 43 | 0 | 3 | 0.54 | 40 (12–76) | 100 (92–100) | 100 (100–100) | 93 (86–100) | – | 0.6 (0.3–1.2) |
| RCA | 12.5 | 48 | 4 | 36 | 6 | 2 | 0.40 | 66 (30–90) | 85 (71–93) | 40 (9–70) | 94 (87–100) | 4.6 (1.8–12) | 0.4 (0.1–1.2) |
| Segment | 3.2 | 720 | 15 | 683 | 14 | 8 | 0.56 | 65 (44–81) | 98 (96–99) | 52 (33–70) | 99 (98–99) | 32 (17–59) | 0.3 (0.2–0.6) |
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