The Value of Left Atrial Strain and Strain Rate for Prediction of Early Postoperative Atrial Fibrillation Following Isolated Off‐Pump Coronary Artery Bypass Grafting in Low‐Risk Patients

ABSTRACT

Background

Following coronary artery bypass grafting (CABG) surgery, postoperative atrial fibrillation (POAF) is a prevalent arrhythmia. Prior research has demonstrated a paucity of reliable approaches to predict early POAF after CABG, particularly in low‐risk subjects. The present investigation proposed to assess how effectively left atrial (LA) strain and LA strain rate predict early POAF after isolated off‐pump CABG (OPCAB) in low‐risk individuals.

Methods

One hundred and twenty‐three low‐risk subjects with sinus rhythm who underwent isolated OPCAB were assessed in this prospective research. The velocity vector imaging (VVI) method was utilized to measure LA strain and LA strain rate. Subsequently, the patients were monitored post‐surgery for 1 week to assess whether early POAF had occurred.

Results

In contrast to those who did not experience early POAF, individuals with early POAF showed significantly lower LA strain (21.25 vs. 37.59, p < 0.001), lower LA strain rate (1.37 vs. 2.73, p < 0.001), and higher left atrial volume index (LAVI) (p < 0.001). A 1‐unit increase in LA strain was associated with a 33% decrease in the odds of early POAF (OR = 0.67, 95% CI: 0.50–0.89; p = 0.006).

Conclusion

Preoperative left atrial strain measurements may serve as an effective predictor of early POAF in low‐risk patients after isolated OPCAB. Rather than treating all patients undergoing CABG, identifying the group at greater risk for early POAF may enable targeted prophylactic therapy.

Postoperative atrial fibrillation is a common complication following coronary artery bypass grafting and may lead to prolonged hospital stays and increased risk of stroke‐related mortality and morbidity. This study found that lower preoperative left atrial strain and strain rate are effective predictors for POAF in low‐risk patients undergoing CABG.

1. Introduction

The most frequent arrhythmia following coronary artery bypass grafting (CABG) is postoperative atrial fibrillation (POAF). This arrhythmia leads to an elevated mortality rate and lengthens hospital stays (Seo et al. 2021). POAF may be discovered in 20%–40% of patients undergoing cardiac surgical procedures (Eikelboom et al. 2021). Furthermore, this arrhythmic event has been acknowledged as a predictor of cerebrovascular strokes following CABG and its related morbidities and mortalities (Laimoud et al. 2022). To prevent the risk of postoperative arrhythmia, prophylactic therapy utilizing beta‐adrenergic blockers has been proven to be effective and is frequently prescribed both before and after cardiac surgery (Khan et al. 2013).

Various underlying risk factors, including left ventricular hypertrophy, COPD, metabolic syndrome, and obesity, have been attributed to POAF (Seo et al. 2021; Zacharias et al. ²⁰⁰⁵; Auer et al. ²⁰⁰⁵; Echahidi et al. ²⁰⁰⁷; Lopes and Agrawal ²⁰²²; Higgs et al. ²⁰²⁰). Intraoperative risk profiles, including atrial injury or ischemia, vascular catheter insertion, abrupt changes in the volume of circulating blood, and operation using cardiopulmonary bypass, have also received attention. Moreover, previous evidence has revealed that functional and structural alterations in the left atrium (LA) contribute to the development and recurrence of atrial fibrillation (AF) as well as localized disruption of electrical conduction (Parsaee et al. 2014). Echocardiographic measurements of LA, including LA size, volume, and function (identified by strain), are valuable tools for recognizing patients with heightened risk of POAF (Reddy Y et al. ²⁰¹⁰; Candan et al. ²⁰¹³).

LA strain is usually measured using 2‐dimensional speckle tracking echocardiography (2D STE), tissue Doppler imaging (TDI), and vector velocity imaging (VVI) (Alimi et al. 2022). VVI is an endocardial border tracking method that remains particularly effective in tracking the movement of structures with thin walls, including the LA. Strain rate imaging can provide valuable insights into assessing compromised atrial contractility, especially in patients with AF. By analyzing data on LA strain rate, it is possible to noninvasively assess atrial reverse remodeling in patients with AF (Her et al. 2013).

Although it has been shown that LA strain is associated with POAF, most available evidence has been derived from heterogeneous cardiac surgery populations, or on‐pump CABG (Misra et al. 2026). Cardiopulmonary bypass induces a substantial inflammatory response that contributes to POAF (Maesen et al. 2012), and on‐pump CABG, compared with off‐pump CABG (OPCAB), is linked to a higher inflammatory response (Mirhafez et al. 2021). Therefore, by selecting low‐risk participants undergoing isolated OPCAB, we sought to minimize the influence of conventional risk factors and cardiopulmonary bypass‐related inflammation. This approach allowed us to more specifically evaluate whether LA strain and LA strain rate may independently predict early POAF. Accordingly, the goal of this study was to evaluate the predictive significance of LA strain and LA strain rate for early POAF after isolated OPCAB in low‐risk patients.

2. Methods and Materials

2.1. Study Setting and Population

In this prospective research, low‐risk individuals with sinus rhythm who were scheduled to undergo isolated OPCAB were enrolled at Ghaem Hospital, Mashhad University of Medical Sciences, Mashhad, Iran.

Low risk was defined as individuals who had only one or no major cardiovascular risk factors, including age ≥ 65, diabetes mellitus, hypertension, history of transient ischemic attack (TIA) or stroke, heart failure, or vascular problems. Individuals who had already experienced AF, chronic lung disease, pulmonary hypertension, or a history of taking anti‐arrhythmic agents were excluded. Demographic and echocardiographic data were gathered for all the individuals recruited in this investigation.

2.2. Echocardiographic Evaluation

One day before CABG surgery, transthoracic echocardiography (TTE) was performed using a Siemens ACUSON SC2000 ultrasound system equipped with a 4V1c transducer (with frequency bandwidth of 1.25–4.5 MHz). Individuals were in the left lateral decubitus position while imaging was conducted.

An echocardiologist followed standard techniques consistent with the latest guidelines of the American Society of Echocardiography (Lang et al. 2015). M‐mode, two‐dimensional, and Doppler measurements were attained.

Left ventricular end‐diastolic and end‐systolic volumes were assessed, and left ventricular ejection fraction (LVEF) was calculated utilizing the Simpson method in the apical 4‐chamber view. Left atrial volume index (LAVI) was measured by a biplane method of discs evaluating LA volume indexed for body surface area. An LAVI value of 34 mL/m² or higher was considered indicative of LA enlargement for both sexes (Lazzeroni et al. 2016).

2.3. Left Atrial Strain Analysis

LA strain was measured by the VVI technique. This technique employs endocardial border tracking to accurately estimate the movement of structures with thin walls like LA (Alimi et al. 2022). Evaluation of LA strain enables a thorough assessment of reservoir, conduit, and contractile performance (Gan et al. 2018). During the reservoir phase, peak LA longitudinal strain was examined.

To perform the VVI method, 2‐dimensional pictures of the apical 2‐ and 4‐chamber views were acquired at frame rates ranging from 70 to 100 frames/s. Moreover, to calculate strain, we employed R R gating. The LA's endocardium was manually traced. The region of interest (ROI) was defined from the lateral to the medial aspect of the mitral annulus, while the pulmonary veins and LA appendage were not included. Measures of LA strain and LA strain rate were computed automatically (Figure 1).

FIGURE 1.

VVI for left atrial strain and left atrial strain rate: (A) VVI tracings of the left atrial endocardial border from the apical four‐chamber view; (B) Longitudinal left atrial strain curve; (C) Segmental strain, volume, and ejection fraction curves in 3 consecutive cardiac cycles and other myocardial deformation parameters; (D) Longitudinal left atrial strain curve and global peak.

2.4. Follow‐Up and ECG Analysis

Following surgery, all subjects were constantly monitored in the ICU and subsequent hospitalization using a central monitoring system. Individuals were monitored for a week in order to look into the occurrence of POAF. Until discharge, 12‐lead ECG recordings were also performed daily. Further ECG recordings were performed if new signs or symptoms, including palpitations, tachycardia, or an irregular pulse, developed. The endpoint of the investigation was defined as the no visible P waves and the presence of irregular R‐R intervals on rhythm strips or 12‐lead electrocardiographic recordings. AF episodes that lasted more than 5 min were counted (Mitchell et al. 2005; Gaudino et al. ²⁰²³).

2.5. Ethical Approval

All individuals enrolled in the study completed informed consent forms. Participants' data were extracted while considering the ethical principles. This study acquired ethical approval from the Organizational Ethics Committee of the Faculty/Region of Mashhad University of Medical Sciences. The ethical approval code was IR.MUMS.MEDICAL.REC.1393.765.

2.6. Statistical Analysis and Report

Quantitative variables were presented as mean ± standard deviation (SD), and qualitative variables were reported using absolute frequencies and percentages. In order to assess the normality of data, the Kolmogorov–Smirnov test was utilized. The χ2 test or Fisher's exact test was implemented for qualitative variables when there were more than 20% of cells with an expected count of less than five. Continuous variables were compared between groups with POAF and without POAF using the Mann–Whitney U test because data were not normally distributed. The correlation between quantitative indices was assessed using Pearson's or Spearman's tests, as appropriate. Independent predictors of early POAF were detected using multivariable logistic regression analysis. SPSS software version 16.0 for Windows (SPSS Inc., Chicago, IL) was utilized for the statistical analysis. p < 0.05 was considered to be statistically significant.

3. Results

This study included 123 patients (50.4% male) who had OPCAB. Regarding cardiovascular risk factors, 35.8% were diabetic, and 43.9% were hypertensive. The mean serum creatinine level was 1.14 ± 0.19 mg/dL (ranging from 0.8 to 1.8 mg/dL). Additionally, the mean LVEF measured by echocardiography was 50.25% ± 7.32% (range: 20%–60%) while the mean strain was 35.59 ± 6.75 (range: 16.3–45.6), the mean strain rate was 2.56 ± 0.60 (range: 1.0–3.6), and the mean LAVI was 25.58 ± 4.62 mL/m² (range: 19–40 mL/m²).

POAF was detected in 15 patients with an overall incidence of 12.2%. Individuals with POAF were older and had a significantly lower LVEF in comparison with those without this arrhythmia (p < 0.001, p = 0.001, respectively). There were no significant variations between the with and without POAF subjects regarding sex (46.7% male versus 50.9% male, p = 0.757), diabetes mellitus (26.7% vs. 37.0%, p = 0.432), and hypertension (40.0% versus 44.4%, p = 0.745). Moreover, there was no significant difference in mean serum creatinine level among both groups with and without POAF (1.14 ± 0.19 versus 1.14 ± 0.20, p = 0.949) (Table 1).

TABLE 1.

Comparison of baseline and echocardiographic characteristics in the groups with and without atrial fibrillation.

Item*	Group with AF (n = 15)	Group without AF (n = 108)	p *
Male sex	7 (46.7)	55 (50.9)	0.757
Age (years)	65.67 ± 3.69	58.94 ± 5.56	< 0.001
History of diabetes mellitus	4 (26.7)	40 (37.0)	0.432
History of hypertension	6 (40.0)	48 (44.4)	0.745
Serum creatinine (mg/dL)	1.14 ± 0.20	1.14 ± 0.19	0.949
LA strain (%)	21.25 ± 5.23	37.59 ± 3.93	< 0.001
LA Strain rate (s−1)	1.37 ± 0.41	2.73 ± 0.41	< 0.001
LA volume index (mL/m2)	32.60 ± 3.56	24.60 ± 3.86	< 0.001
LVEF (%)	44.60 ± 11.16	51.04 ± 6.30	0.001

^*Bold values indicate statistically significant results.

Based on our analysis, patients with POAF had significantly lower LA strain (21.25 vs. 37.59, p < 0.001), lower strain rate (1.37 vs. 2.73, p < 0.001), and higher LAVI (p < 0.001) when compared to patients without POAF (Table 1 and Figure 2).

FIGURE 2.

Boxplots of echocardiographic variables in patients. (A) Echocardiographic variables in individuals without atrial fibrillation, (B) Echocardiographic variables in individuals with atrial fibrillation. EF, ejection fraction; SR, strain rate.

Correlation analysis showed that both LA strain and LA strain rate were negatively correlated with age (r = −0.359 and r = −0.345, respectively; both p < 0.001); however, LAVI was positively correlated with age (r = 0.319, p < 0.001) (Table 2).

TABLE 2.

Correlation matrix of clinical and echocardiographic variables.

		Age	Creatinine	LVEF	Strain	Strain rate	LA volume
Age	Pearson Correlation	1	−0.127	−0.224	−0.359	−0.345	0.319
	p Value*		0.162	0.013	< 0.001	< 0.001	< 0.001
Creatinine	Pearson Correlation	—	1	0.133	0.042	0.031	−0.066
	p Value	—		0.142	0.641	0.730	0.466
LVEF	Pearson Correlation	—	—	1	0.527	0.527	−0.566
	p Value	—	—		< 0.001	< 0.001	< 0.001
Strain	Pearson Correlation	—	—	—	1	0.967	−0.748
	p Value	—	—	—		< 0.001	< 0.001
Strain rate	Pearson Correlation	—	—	—	—	1	−0.751
	p Value	—	—	—	—		< 0.001
LA volume	Pearson Correlation	—	—	—	—	—	1
	p Value	—	—	—	—	—

^*Bold values indicate statistically significant results.

Multivariate logistic regression analysis demonstrated that LA strain was the only independent predictor of POAF (OR = 0.67, 95% CI: 0.50–0.89; p = 0.006). The analysis indicates that each 1‐unit increase in LA strain is associated with a 33% reduction in the odds of developing POAF (Table 3).

TABLE 3.

Multivariable logistic regression analysis of predictors of early postoperative atrial fibrillation.

Variable	Odds ratio	95% confidence interval	p
Age	2.01	0.92–3.36	0.07
Left atrial strain (%)	0.67	0.50–0.89	0.006
Left atrial volume index (mL/m2)	1.70	0.77–3.73	0.18

4. Discussion

We designed this prospective investigation in order to examine the predictive significance of LA strain and LA strain rate for early POAF after isolated OPCAB in low‐risk subjects. Our study demonstrated that individuals who experienced early POAF had significantly lower strain and strain rate and higher LAVI than those who did not. Nevertheless, only LA strain remained an independent predictor of early POAF, following multivariable adjustment.

In general populations, the incidence of AF is about 1.8% (Schnabel et al. 2012; Teh et al. ²⁰²³). For those under 70 years old, the rate is only 0.4%, while it increases to 2%–4% for individuals over 70 and up to 18% for those aged 80 years and above (Teh et al. 2023; Norberg et al. ²⁰¹³). This frequency is about 5% in subjects undergoing general surgical procedures (Alqahtani 2010). Among the hospitalized population, this frequency ranges from 8% to 14% (Shi et al. 2002). The reported incidence of AF in patients undergoing open cardiac operations is much greater, varying between 3.1% and 91%, with large‐scale studies suggesting a rate of approximately 30% (Ellis 2013; Kawczynski et al. ²⁰²¹). In our study, which focused on low‐risk patients, an average incidence of 12.1% was detected for early POAF, which is lower than that described in earlier research. Our selection of low‐risk patients may partly explain this disparity. By minimizing the impact of conventional risk factors, this approach enabled a more focused assessment of the contribution of left atrial function to the early POAF development. The other possible explanation is the short follow‐up period, which may have contributed to the underestimation of the true incidence.

Previous literature has identified that increasing age and enlargement of the left atrium were independent predictors of POAF (Wang et al. 2012; Nakai et al. ²⁰⁰²; Somesarayi et al. ²⁰²³). The incidence of AF varies with age, with an OR of 1.60 per decade of additional life, ranging from 13% for subjects under 50 to 52% for those over 80. This finding aligns with prior investigations indicating POAF is reliably predicted by older age (Her et al. 2013; Schnabel et al. ²⁰¹²; Norberg et al. ²⁰¹³). The heart may undergo structural alterations as we age, including increased chamber size and fibrosis (Di Salvo et al. 2005; Verdejo et al. ²⁰¹⁶). In our study, subjects who experienced early POAF were significantly older than those who did not. However, age was not an independent predictor of early POAF after conducting multivariable logistic analysis. This finding may be caused by the relatively homogeneous, low‐risk nature of our study population and the limited number of POAF events. Moreover, in line with some previous reports, we did not find any significant differences between the subjects with and without POAF regarding sex (Hashemzadeh et al. 2013; Abdelrazek et al. ²⁰²¹).

According to various studies, POAF tends to happen in the first 5 days after surgery, peaking on the 2nd post‐operative day (Parsaee et al. 2014; Zhang et al. ²⁰²³). Although the etiology of POAF remains uncertain (Zhang et al. 2023; Tayyareci et al. ²⁰¹⁰), numerous factors, including surgical trauma, insufficient cooling of the atrium, inadequate preservation of atrial tissue by cardioplegia, post‐operative pericarditis, elevated sympathetic function, euthyroid sick syndrome, and withdrawal from beta‐blockers, have been suggested as potential contributors (Shi et al. 2002; Ellis ²⁰¹³; Di Salvo et al. ²⁰⁰⁵). The hypothesis of “dispersion of refractoriness” appears to be a reasonable description, presuming that the susceptibility of atrial tissue to the development of AF is caused by dispersion or deficiency in conformity of atrial refractory periods as the underlying mechanism (van Staveren and de Groot ²⁰²⁰).

LA size is a widely employed parameter to investigate structural changes in LA. Research has elaborated that development of AF in the general population can be predicted by LA size (including diameter and volume) (Haffajee et al. 2011). Due to the asymmetry and enlargement of the chamber, volume has been considered a more accurate evaluation of left atrial size compared to diameter (Tsang et al. 2006). Osranek et al. (2006) evaluated patients who underwent CABG and concluded LAVI greater than 32 mL/m² was an indicator of POAF. Regardless of age and other clinical parameters, individuals with LAVI above this threshold had a five‐fold higher probability of POAF occurrence. In accordance with previous studies, our research also indicated larger LAVI values were detected in patients with POAF (p < 0.01). However, after conducting multivariable logistic regression, LAVI did not remain an independent predictor. In contrast, strain of LA remained as an independent predictor, which may suggest that impaired atrial function precedes structural remodeling in low‐risk patients; yet, this interpretation should be made with caution.

Regional deformation of LA walls and global LA function can be noninvasively evaluated by TDI, VVI, and 2D STE (Vieira et al. 2014; Mor‐Avi et al. ²⁰¹¹; Motoki et al. ²⁰¹²). Previous studies have demonstrated that preoperative LA strain can predict POAF in adult patients who undergo cardiac surgery (Misra et al. 2026). Tayyareci et al. (2010) showed that early diastolic strain rate, systolic strain rates, and LA strain assessed by VVI were independent markers to predict POAF in patients undergoing CABG. Similarly, Gabrielli et al. (2011) reported that LA strain and LA strain rate measured by STE were lower in this population. Likewise, in patients undergoing mitral valve surgery, LA longitudinal strain can predict the occurrence of POAF. This parameter could potentially facilitate risk stratification by detecting individuals at greater risk of POAF. Moreover, it will guide cardiologists in selecting appropriate intensive prophylactic anti‐arrhythmic therapy (Candan et al. 2013).

It has been suggested that pre‐operative LA dysfunction is an important factor in developing POAF through neurohumoral activation and enhanced atrial electrical vulnerability (Tayyareci et al. 2010). Cameli et al. (2012) reported that global positive strain is an independent predictor of cardiovascular events, beyond the standard factors commonly used for LA investigation. In our study, by restricting our participants to low‐risk patients undergoing isolated OPCAB, we sought to minimize the influence of conventional risk factors and cardiopulmonary bypass‐related inflammation. This approach allowed us to more specifically determine whether impaired LA function could predict early POAF.

Different studies in subjects with AF have highlighted that LA strain predicts success in sinus rhythm restoration following ablation or electrical cardioversion. Additionally, it predicts the likelihood of recurrence of AF following successful cardioversion (Thomas et al. 2007; Kuppahally et al. ²⁰¹⁰). Azemi et al. (2012) revealed that decreased LA strain could serve as a sensitive marker for elevated risk of stroke or TIA in individuals with low‐risk CHADS2 scores, AF, and a history of TIA or stroke. These outcomes indicate that strain may be a beneficial measure for decision‐making regarding the prescription of oral anticoagulation in this population.

There may be some possible limitations in this study. First, our work was carried out at a single center, and the sample size was relatively small. This limitation may restrict the external validity of our results. Secondly, the low number of POAF events may have limited the statistical power and stability of our multivariable logistic regression model, resulting in relatively wide confidence intervals for some variables. Hence, the predictive performance of the model should be interpreted cautiously and requires external validation in larger cohorts. Thirdly, given that most POAF occurs within the early postoperative period, our patients were followed for 1 week after surgery; however, some episodes of POAF may have occurred after this period, which results in POAF underestimation. Future studies with a larger sample size and longer follow‐up are warranted to validate the results of our investigation in low‐risk subjects undergoing isolated OPCAB.

5. Conclusion

Preoperative LA strain measurements may serve as an independent predictor of early POAF in low‐risk subjects after isolated OPCAB. Identifying the group at elevated risk of early POAF may enable targeted prophylactic treatment rather than targeting all patients undergoing OPCAB. Future research with a prolonged follow‐up and a larger study population is required to further evaluate our findings in low‐risk patients undergoing isolated OPCAB.

Author Contributions

L.B. and S.B. conceived and designed the study. L.B., S.B., and A.A. collected the data. L.B., S.B., N.E., and A.A. conducted the literature search. M.E., S.B., and N.E. analyzed the data and performed the statistical analysis. L.B., S.B., M.E., N.E., and O.M. interpreted the data. L.B., S.B., O.M., and N.E. drafted the article. All the authors critically revised this article and approved the final version of the manuscript.

Funding

The authors have nothing to report.

Ethics Statement

This study fully meets the terms of the Declaration of Helsinki. The study acquired ethical approval from the Organizational Ethics Committee of the Faculty/Region of Mashhad University of Medical Sciences. The ethical approval code was IR.MUMS.MEDICAL.REC.1393.765.

Consent

All individuals enrolled in the study completed informed consent forms.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.