Summary
Background
Postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery, with increased risk of embolic events, haemodynamic instability, haemorrhagic complications and prolonged hospital stay.
Aims
We sought to assess the value of preoperative left ventricular global longitudinal strain (GLS) for the prediction of POAF in a series of patients with severe symptomatic aortic stenosis who underwent aortic valve replacement (AVR).
Methods
Fifty-eight consecutive patients (52% men) aged 73 ± 9 years, with severe symptomatic aortic stenosis (aortic valve area < 1 cm 2 or < 0.5 cm 2 /m 2 ), in sinus rhythm, who underwent AVR were prospectively included in three centres between 2009 and 2010. Complete preoperative echocardiography was performed in all patients, including global and segmental longitudinal strain using two-dimensional speckle tracking.
Results
The POAF incidence was 28/58 (48%). On univariate analysis, aortic valve area ( P = 0.04), preoperative E/e’ ratio ( P = 0.04) and GLS ( P = 0.005) were associated with the occurrence of POAF. Chronic obstructive pulmonary disease ( P = 0.05), preoperative statin treatment ( P = 0.09), age ≥ 80 years ( P = 0.09), left ventricular ejection fraction ( P = 0.09) and systolic pulmonary artery pressure ( P = 0.06) tended to increase the risk of POAF. The best GLS cut-off value for the prediction of POAF was –15% (82% sensitivity, 53% specificity, area under the curve 0.72). On multivariable analysis, GLS > –15% was the only independent predictor of POAF (odds ratio 7.74, 95% confidence interval [1.15–52.03]; P = 0.035).
Conclusions
Incidence of POAF is high after AVR for severe aortic stenosis. Our results suggest an additive value of the study of left ventricular myocardial deformation to classical clinical and echocardiographic variables for the prediction of POAF in this setting.
Résumé
Contexte
La fibrillation atriale postopératoire (FAPO) est une complication courante après chirurgie cardiaque, augmentant le risque d’épisodes emboliques, hémorragiques, d’instabilité hémodynamique, prolongeant l’hospitalisation.
Objectifs
Évaluer l’apport de l’étude de la déformation longitudinale du ventricule gauche en utilisant l’imagerie bidimensionnelle ( strain global longitudinal [SGL]) pour prédire la survenue de la FAPO après remplacement valvulaire aortique (RVA) pour rétrécissement aortique serré (RAC) symptomatique.
Méthodes
Cinquante-huit patients consécutifs (52 % d’hommes), âgés de 73 ± 9 ans, porteurs d’un RAC serré symptomatique (défini par une surface aortique < 1 cm 2 ou < 0,5 cm 2 /m 2 ), en rythme sinusal, et opérés d’un RVA ont été inclus prospectivement dans trois centres entre 2009 and 2010. Une échocardiographie complète incluant le SGL a été realisée avant chirurgie chez tous les patients.
Résultats
L’incidence de la FAPO était de 28/58 (48 %). En analyse univariée, la surface aortique ( p = 0,04), le rapport E/e’ préopératoire ( p = 0,04) et le SGL ( p = 0,005) étaient associés à la survenue de FAPO. La bronchopathie obstructive chronique ( p = 0,05), le traitement par statine en préopératoire ( p = 0,09), l’âge ≥ 80 ans ( p = 0,09), la fraction d’éjection ventriculaire gauche ( p = 0,09) et la pression artérielle pulmonaire systolique ( p = 0,06) tendaient vers la significativité pour prédire la FAPO. Le meilleur seuil de SGL pour prédire la FAPO était de –15 % (82 % de sensitivité, 53 % de spécificité, aire sous la courbe 0,72). En l’analyse multivariée, le SGL supérieur à –15 % était le seul prédicteur indépendant de FAPO (OR 7,74 [1,15–52,03], p = 0,035).
Conclusions
La FAPO est fréquente après RVA pour RAC serré. Nos résultats suggèrent une valeur additionnelle de l’étude de la déformation longitudinale du ventricule gauche par imagerie échographique bidimensionnelle aux paramètres cliniques et échographiques classiques pour prédire la FAPO.
Background
Postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery. It is associated with increased risk of embolic events, haemodynamic instability, heart failure and haemorrhagic complications, and it often prolongs the duration of hospital stay. The incidence of POAF after valvular surgery is high, ranging from 33% to 49% . In severe aortic stenosis, chronic left ventricular pressure overload induces left ventricular hypertrophy that leads to adequate wall stress and normal left ventricular ejection fraction (LVEF). Nevertheless, recent studies conducted in patients with severe aortic stenosis and normal LVEF have demonstrated, in a significant number of cases, abnormal global myocardial deformation – particularly impaired longitudinal contraction . Thus, left ventricular hypertrophy induces both systolic and diastolic dysfunction, leading to progressive left atrial dilatation and atrial fibrillation (AF). Therefore, in the present study conducted in a series of patients with severe symptomatic aortic stenosis, we sought to assess the value of left ventricular global longitudinal strain (GLS) for the prediction of POAF after aortic valve replacement (AVR).
Methods
Study population
Fifty-eight consecutive patients (30 men, 52%) aged 73 ± 9 years, in sinus rhythm at inclusion, with severe symptomatic isolated aortic stenosis (aortic valve area < 1 cm 2 or indexed aortic valve area < 0.5 cm 2 /m 2 ) who underwent AVR were prospectively included in three centres (Amiens, Lille and Compiègne). The study was approved by local review boards and informed consent was obtained from the patients before all procedures. Exclusion criteria were: severe co-morbidities precluding AVR surgery; more than mild aortic or mitral regurgitation; and permanent AF. All patients underwent preoperative coronary angiography. Reduction of the normal diameter by ≥ 50% was considered to define significant coronary artery stenosis in the left main coronary artery. A cut-off value of 70% was used for the right coronary, left anterior descending and circumflex arteries. Multivessel coronary artery disease was defined as significant stenoses in two or more vessels.
Definition of atrial fibrillation
During the stay in the intensive care unit, the electrocardiogram was continuously monitored and recorded. During the entire hospital stay, 12-lead electrocardiograms were performed daily until discharge and if requested by the physician or in case of symptoms. POAF combined paroxysmal and persistent AF. Paroxysmal AF was defined as self-terminating AF, usually within 48 hours . Persistent AF was defined as an AF episode that lasted longer than 7 days or required termination by cardioversion .
Echocardiography
Echocardiographic examinations were performed using commercially available ultrasound machines (Vivid 7 and Vivid e9; GE Healthcare, Norway). All echocardiographic and Doppler data were obtained in digital format and stored for off-line analysis. Left ventricular and left atrial dimensions were measured according to the American Society of Echocardiography and European Association of Echocardiography guidelines . Left atrial volume was obtained using the biplane area length method from apical four-chamber and two-chamber views and was indexed to body surface area. LVEF was measured using the biapical Simpson method. Left ventricular diastolic function was assessed by E-wave and A-wave velocities, the deceleration time of the E-wave, and the E/A ratio from the mitral inflow. Aortic valve area was calculated using the continuity equation and was indexed for the body surface area. Pulsed-wave tissue Doppler imaging velocities were assessed at the basal segments of each of the two longitudinal planes in apical four-chamber and two-chamber views. Peak systolic (s’), early (e’) and late (a’) diastolic tissue Doppler annular velocities were averaged and the E/e’ ratio was calculated.
Left ventricular longitudinal strain study
Left ventricular longitudinal strain quantification was performed using commercially available software (EchoPAC, versions BT06 and BT08; GE Healthcare, Norway). Standard two-dimensional grey-scale loops of the left ventricle were acquired in conventional apical four-chamber, two-chamber and long-axis views. Data were stored digitally and transferred for off-line analysis. Special care was taken to ensure frame rates of between 50 and 90 frames per second in all patients. The regions of interest were defined manually by marking the endocardial border. The automatic tracking of the endocardial contour was verified carefully and the region of interest was corrected manually to ensure optimal tracking of the entire myocardial wall. Segmental strain analysis was performed by dividing each left ventricular image into six segments. Peak systolic longitudinal strain was calculated by averaging the peak systolic values of the 18 segments, derived from the three apical views. Reproducibility in the GLS measurement was 0.57 ± 0.77% in a previous study by our group . In our study, 94% (983/1044) of the myocardial segments were adequately tracked.
Statistical analysis
Continuous variables were tested for normal distribution by the use of the Kolmogorov–Smirnov test. Variables not normally distributed were expressed as medians (interquartile ranges). Normally distributed continuous variables were expressed as mean values ± 1 standard deviation. Categorical variables were summarized as frequency percentages and absolute numbers. The comparison of continuous variables between patients with and without POAF was carried out by use of the Mann–Whitney U test. Frequencies of categorical variables were compared with the χ 2 test or Fisher’s exact test, as appropriate. Receiver operating characteristic (ROC) curve analysis was used to identify the best cut-off values for GLS for predicting POAF. An epidemiological approach was taken. Factors thought to be important for the endpoint and variables significantly different on univariate analysis with a P value < 0.10 were entered into the multivariable analyses (logistic regression analyses). These variables were: age, sex, body mass index, preoperative AF, hypertension, diabetes, chronic obstructive pulmonary disease (COPD), multivessel coronary disease, preoperative statin treatment, indexed left atrial volume > 30 mL/m 2 , LVEF > 50%, aortic valve area < 0.7 cm 2 and GLS > –15%. Model discrimination was assessed with ROC analysis by computing the area under the ROC curve (AUC). Calibration of the model was tested with the Hosmer–Lemeshow test. Overall model performance was also assessed with the likelihood ratio, which indicates the degree to which the pretest probability of an event is altered by information provided by a predictive model. The higher the model likelihood ratio, the greater the probability of accurately predicting events. A two-sided P value < 0.05 was considered statistically significant. Statistical analysis was performed using SPSS 13.0 statistical software (SPSS Inc., Chicago, IL, USA) and STATA (version 10; StataCorp LP, College Station, TX, USA).
Results
Study population
Baseline data from the 58 study patients, overall and according to the occurrence of POAF, are presented in Tables 1 and 2 . All 58 patients had severe symptomatic aortic stenosis (mean aortic valve area of 0.70 ± 0.17 cm 2 ; range 0.3–1 cm 2 ). None of the patients had a mean transvalvular gradient < 30 mmHg. Mean LVEF was 60 ± 11%, range 30 to 83%. LVEF was ≤ 50% in only six (10%) patients. Symptoms were dyspnoea in 88% (51/58), angina in 43% (25/58) and syncope in 14% (8/58). Mean preoperative New York Heart Association class was 2.1 ± 0.6. Significant coronary artery disease was found in 22 (38%) patients. Before surgery, 19 (33%) patients had beta-blocker therapy, four (7%) patients had amiodarone therapy and 36 (62%) received a statin. Bioprostheses were implanted in 49/58 (84.5%) and mechanical prostheses in 9/58 (15.5%). Concomitant coronary artery bypass graft (CABG) was performed in 10 patients (17%). Perioperative mortality was 1/58 (1.7%); this patient died of respiratory failure on the 23rd postoperative day. Significant pericardial effusion needing surgical treatment was found in five patients (9%) and pulmonary infection in seven patients (12%).
| Variable | Overall population | Postoperative atrial fibrillation | P a | |
|---|---|---|---|---|
| No | Yes | |||
| ( n = 58) | ( n = 30; 52%) | ( n = 28; 48%) | ||
| Age (years) | 73 ± 9 | 72 ± 9 | 74 ± 9 | 0.32 |
| Age ≥ 80 years | 17 (29) | 6 (20) | 11 (39) | 0.09 |
| Men ( n ; %) | 30 (52) | 17 (57) | 13 (46) | 0.60 |
| Height (cm) | 166 ± 12 | 166 ± 12 | 165 ± 12 | 0.74 |
| Weight (kg) | 76 ± 16 | 75 ± 18 | 77 ± 14 | 0.77 |
| Body mass index | 28 ± 5 | 27 ± 5 | 28 ± 5 | 0.40 |
| Body surface area (kg/m 2 ) | 1.83 ± 0.22 | 1.83 ± 0.25 | 1.82 ± 0.18 | 0.85 |
| Preoperative paroxysmal atrial fibrillation | 10 (17) | 3 (10) | 7 (25) | 0.13 |
| Amiodarone treatment | 4 (7) | 2 (7) | 2 (7) | 0.94 |
| Beta-blocker treatment | 19 (33) | 10 (33) | 9 (32) | 0.92 |
| Statin treatment | 36 (62) | 22 (73) | 14 (50) | 0.09 |
| ACE inhibitor treatment | 27 (47) | 15 (50) | 12 (43) | 0.61 |
| Hypertension | 41 (71) | 21 (70) | 20 (71) | 0.90 |
| Diabetes mellitus | 17 (29) | 8 (27) | 9 (32) | 0.77 |
| Dyslipidaemia | 33 (57) | 16 (53) | 17 (61) | 0.60 |
| Multivessel coronary artery disease | 22 (38) | 14 (47) | 8 (28) | 0.22 |
| Chronic obstructive pulmonary disease | 9 (15) | 2 (7) | 7 (25) | 0.05 |
| Associated coronary artery bypass graft | 10 (17) | 7 (23) | 3 (11) | 0.30 |
| Cardiopulmonary bypass time (minutes) | 79 ± 29 | 81 ± 28 | 77 ± 30 | 0.57 |
| Cross-clamp time (minutes) | 57 ± 21 | 59 ± 23 | 54 ± 20 | 0.43 |
| Aortic prosthesis type | ||||
| Mechanical | 9 (15.5) | 5 (17) | 4 (14) | 0.80 |
| Bioprosthesis | 49 (84.5) | 25 (83) | 24 (86) | |
| Postoperative troponin peak | 7 ± 5 | 7 ± 6 | 8 ± 5 | 0.62 |
| Aortic prosthesis size (mm) | 22 ± 2 | 22 ± 2 | 23 ± 2 | 0.28 |
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