Raffaella , Antonio , Rosanna , Cristina , Elisa , Marta , Matteo , and Sergio: Left atrial strain predicts postoperative atrial fibrillation in patients undergoing major orthopaedic surgery.

Introduction

The prevalence of atrial fibrillation (AF) is approximately 1.5-2% in the general population. About 70% of affected subjects are 65 and 85 years old. This arrhythmia is associated with a five-fold risk of stroke and three-fold incidence of congestive heart failure, and higher mortality. The occurrence of AF represents a common complication in patients undergoing major orthopaedic surgery and is often associated with prolonged hospitalization. In addition, AF leads to a worse prognosis, resulting in a higher morbidity and mortality. The high incidence of postoperative AF in orthopaedic surgery alerts the importance of identifying patients at higher risk.

Speckle tracking echocardiography (STE) is an echocardiographic technique that analyzes standard B-mode images for a semi-automated evaluation of myocardial deformation. Quantification of LA strain by speckle tracking has been recently proposed to analyze LA function, and has shown clinical potential utilities.

The aim of this study was to analyze LA deformation by STE in patients undergoing major orthopaedic surgery and correlate these parameters with the occurrence of post-operative AF.

Methods

Study population

One hundred and fifteen patients (mean age 74±12 years), undergoing elective (n=39; 41.9%) or post-traumatic (n=54; 58.0%) orthopaedic surgery, were prospectively enrolled. Exclusion criteria were: age<18 yeas old, non sinus rhythm, mechanical ventilation, severe mitral and/or aortic regurgitation, mitral and/or aortic stenosis, presence of prosthetic mitral and/or aortic valve, heart transplantation or a poor quality echocardiography imaging. All procedures were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. Informed consent was obtained from all patients to be included in the study.

All patients underwent standard echocardiographic examination the day before surgery. Both standard echocardiographic parameters, and peak atrial longitudinal strain (PALS) were measured in all subjects. PALS values were obtained by averaging all segments measured in the 4- and 2-chamber views (global PALS). The occurrence of AF episodes was monitored until home discharge.

Table 1

Preoperative characteristics with subdivision into groups of postoperative atrial fibrillation (POAF) and sinus rhythm (no POAF).

no POAF n=67 POAF n=26 HR (95% CI) P value
Age (year) 70.2 ± 12.1 77.1 ± 5.1 1.05 (1.03-1.06) <0.0001
Female (%) 41.3 44.1 1.01 (0.99-1.02) 0.34
BMI (kg/m2) 28.2 ± 7.1 29.5 ± 8.1 1.05 (0.95-1.07) 0.15
NYHA (1-4) 1.07 ± 1.1 1.30 ± 1.2 1.05 (1.02-1.07) 0.005
Hypertension (%) 70 71 1.01 (0.99-1.02) 0.42
Diabetes mellitus (%) 15 18 1.01 (0.99-1.01) 0.64
Dyslipidemia 65 68 1.01 (0.99-1.02) 0.45
Smoking 29.6 35.2 1.04 (0.99-1.07) 0.14
Pulmonary disease (%) 12.2 19.2 1.07 (1.01-1.07) 0.03

Table 2

Preoperative echocardiographic variable

no POAF n=67 POAF n=26 HR (95% CI) P value
Heart rate 76.2 ± 14.2 77.2 ± 16.1 1.01 (0.99-1.01) 0.66
End-diastolic LV diameter (mm) 48.2 ± 6.2 50.2 ± 7.9 1.01 (0.97-1.02) 0.32
LV mass index (g/m2) 127.2 ± 38.2 121.6 ± 37.4 0.97 (0.95-1.02) 0.42
LV Ejection Fraction (%) 57.6 ± 7.9 58.5 ± 7.9 1.00 (0.99-1.01) 0.75
LA volume indexed (ml/m2) 42.6 ± 15.2 46.9 ± 17.1 1.02 (1.01-1.04) 0.05
Mitral E/A ratio 0.71 ± 0.41 0.79 ± 0.40 1.00 (0.99-1.01) 0.71
E/e’ ratio 12.1 ± 6.1 16.2 ± 7.1 1.03 (0.98-1.05) 0.08
PAPs (mmHg) 35.1 ± 11.6 39.2 ± 15.4 1.02 (0.98-1.06) 0.16
Global PALS (%) 34.6 ± 9.5 22.0 ± 7.1 1.09 (1.05-1.15) <0.0001
Global PALS < 15.3% (%) 41.1 91.6 7.76 (2.95-19.3) <0.0001

Standard echocardiography

The day before surgery, echocardiographic studies were performed using a high quality echocardiograph (Vivid 7, GE, USA). Subjects were studied in the left lateral recumbent position. Measurements of left ventricular (LV) and LA dimensions were made in accordance with current American Society of Echocardiography recommendations. LV ejection fraction was measured using the modified biplane Simpson’s rule. The ratio between peak early (E) and late (A) diastolic LV filling velocities and E wave deceleration time were determined by standard Doppler imaging. The timings of mitral and aortic valve opening and closure were defined by pulsed wave Doppler tracings of mitral inflow and LV outflow.

Speckle tracking

For speckle tracking analysis, apical four- and two-chamber views images were obtained using conventional two dimensional gray scale echocardiography, during breath hold with a stable ECG recording. Particular attention was given to obtain an adequate gray scale image, allowing reliable delineation of myocardial tissue and extracardiac structures. Three consecutive heart cycles were recorded and averaged. The frame rate was set between 60 and 80 frames per second. These settings are recommended to combine temporal resolution with adequate spatial definition, and to enhance the feasibility of the frame-to frame tracking technique.

Recordings were processed using an acoustic-tracking software (Echo Pac, GE, USA), allowing off-line semi-automated analysis of speckle-based strain. LA endocardial surface was manually traced in both four- and two-chamber views by a point-and-click approach. An epicardial surface tracing was then automatically generated by the system, thus creating a region of interest (ROI). After manual adjustment of ROI width and shape, the software divided the ROI into 6 segments, and the resulting tracking quality for each segment was automatically scored as either acceptable or non-acceptable, with the possibility of further manual correction. Segments in which no adequate image quality could be obtained were rejected by the software and excluded from the analysis. Lastly, the software generated strain curves for each atrial segment. In subjects with adequate image quality, a total of 12 segments were then analyzed. To trace the ROI in the discontinuity of LA wall corresponding to pulmonary veins and LA appendage, the direction of LA endocardial and epicardial surfaces at the junction with these structures was extrapolated. Peak atrial longitudinal strain (PALS) was calculated by averaging values observed in all LA segments (global PALS), and by separately averaging values observed in 4- and 2-chamber views (4- and 2-chamber average PALS).5 In patients in whom some segments were excluded because of the difficulty in achieving adequate tracking, PALS was calculated by averaging values measured in the remaining segments.(Figure 1) Reproducibility of PALS measurements has been assessed in our previous study 5.

Statistical analysis

Data are shown as mean ± SD. Inter- and intra-observer reproducibility was assessed by calculating variability coefficients. Reference values were expressed as mean ± SD and 5–95° percentile ranges. Comparisons were performed using the Student t test for paired data. A P value < 0.05 was considered statistically significant. Analyses were performed using the SPSS (Statistical Package for the Social Sciences, Chicago, Illinois) software Release 11.5.

Results

Of 115 patients screened, 93 met eligibility criteria during the study period: 49 underwent hip surgery, 28 knee surgery and 16 surgery of the shoulder/elbow. Five were excluded for severe mitral valve disease, 4 for poor echocardiographic window and 1 for severe aortic stenosis. All patients received a standard postoperative care (Table 1). No major surgical complications were recorded. Postoperative AF (POAF) occurred in 26 patients (27.9%). (Table 2)

Patients with POAF episodes were significantly older (No POAF patients 70.2±12.1, POAF 77.1± 5.1, p<0.0001), presented higher prevalence of pulmonary disease (No POAF 12.2, POAF 19.2, p=0.01), higher E/e’ ratio (No POAF 12.1±6.1, POAF 16.2±7.1, p=0.005) and lower levels of global PALS (No POAF 34.6± 9.5, POAF 22.0 ± 7.1 p<0.0001). After multivariate analysis, including age, LV ejection fraction, global PALS, E/e’ ratio and LA volume, global PALS (β=-0.660, p < 0.0001), LA indexed volume (β=0.326, p < 0.0001) and age (β= 0.198, p < 0.0001) independently predicted the POAF episodes. Global PALS ratio was the strongest predictor, accounting for 66.3% of the total variability explained by the model.

Figure 1

Peak atrial longitudinal strain (PALS)

icfj.2014.1.4.189-g001.jpg

Figure 2

AUC of Global PALS, LA Volume indexed, E/e’ Ratio

icfj.2014.1.4.189-g002.jpg

Among all clinical and echocardiographic variables analyzed, global PALS demonstrated the highest diagnostic accuracy (AUC of 0.88) and, with a cutoff value less than 15.3%, good sensitivity and specifi city of 89% and 90%, respectively, to predict postoperative AF episodes. LA volume indexed and E/e’ ratio had lower diagnostic accuracy (AUC 0.70 and 0.49, respectively). (Figure 2).

Discussion

In this study, we investigated the predictive value and the relationship of atrial longitudinal strain with new-onset AF in patients undergoing orthopaedic surgery. Atrial fi brillation is a relatively frequent complication of cardiac surgery, occurring in approximately 25-40% of patients following CABG. In our study, postoperative AF occurred in 27.9% of patients. All patients received continuous 24-hour telemetry with arrhythmia-detection algorithms during their hospital stay. It is well known that postoperative AF is associated with increased mortality and morbidity. Moreover, postoperative AF may lead to longer intensive care, prolonged hospitalization and significantly increased costs. Although new-onset postoperative AF is usually a transient arrhythmia, it is associated with a five-fold risk of stroke and a three-fold incidence of congestive heart failure. Postoperative AF may also cause myocardial infarction and ventricular arrhythmias that can lead even to death in high-risk patients. It has been demonstrated that surgery, structural heart disease and ageing predispose AF. In our study, age was an independent predictor of postoperative AF. Kalman et al. showed that advanced age is associated with increasing circulating norepinephrine levels that increase the incidence of AF. On the other hand, there is a slight discrepancy between the peak of sympathetic activation, which occurs within 24 hour post operatively, and the onset of postoperative AF, mostly developing between 48 and 72 hour after surgery. Several studies showed that the oxidative stress can have a role in the occurrence of postoperative AF; in particular Carnes et al. showed that administration of ascorbate to patient undergoing CABG decreases the incidence of postoperative AF.

LA function can be analyzed by two-dimensional echocardiography, Doppler analysis of transmitral and pulmonary vein fl ow, and Tissue Doppler (TD) assessment of LA myocardial velocities, but its quantifi cation until few year ago remained a challenging issue. Two-dimensional strain imaging is an echocardiographic technique that uses standard B-mode images for speckle tracking analysis. The speckle pattern (acoustic backscatter generated by the refl ected ultrasound beam) is followed frame-by-frame, using a statistical approach based on the detection of the best matching area. The displacement of this speckle pattern is considered to follow myocardial movement, and a change between speckles is assumed to represent myocardial deformation. STE allows a non invasive assessment of global LA function and regional deformation of LA walls; two-dimensional strain imaging successfully provides LA volume curves during one cardiac cycle, from which various LA mechanical indices can be obtained and allows a direct assessment of LA contractility and passive deformation 6. Several studies have shown that strain imaging can detect LA dysfunction and correlate with LA fi brosis. This property could potentially explain the capacity of this parameter in predicting AF burden.

Conclusions

STE analysis of LA myocardial deformation could be considered a promising tool for the evaluation of LA subclinical dysfunction in patients undergoing orthopaedic surgery, giving a potentially better risk stratification for the occurrence of postoperative AF.

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Copyright (c) 2015 Rafaella de Vito, Antonio Di Giovanni, Rosanna Reccia, Cristina Di Tommaso, Elisa Bigio, Marta Focardi, Matteo Cameli, Sergio Mondillo

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