Off-pump coronary artery bypass grafting (OPCABG) is a major treatment approach for complicated and advanced coronary artery disease [1, 2]. OPCABG avoids the negative influence of cardioplegia on the myocardium tissue, ischemia-reperfusion damage, and systemic inflammatory response from on-pump coronary artery bypass grafting (CABG) [3]. Despite its value, there is a high risk of postoperative cardiac and noncardiac complications resulting from OPCABG [3, 4, 5]. The most frequently observed cardiac dysrhythmia in these patients is new-onset postoperative atrial fibrillation (POAF) [6, 7]. POAF carries an incidence rate of 10–40% and a peak onset at two days [4, 8]. This remains a significant challenge when considering increased hospital stays and health care costs, and most notably an increased morbidity rate [9]. Despite progress in medical and surgical treatments, the overall incidence of new-onset POAF has not significantly improved [10]. Therefore, it is a clinical imperative to identify patients who are at risk for new-onset POAF early during the perioperative period as this ensures adequate precautions and optimization of clinical outcomes.

A growing number of studies indicate that excess visceral adiposity, which promotes delivery of high doses of adipokines to the heart tissues, results in atrial inflammation and myocardial lipidosis [11]. These events are associated with an increased risk of cardiovascular disease (CVD) and mortality [12, 13, 14]. Previous studies have demonstrated that insulin resistance (IR), which leads to abnormal lipid deposition and proinflammatory states, plays a key role in individuals with cardio-metabolic disorders [15]. Nevertheless, clinical evidence regarding the association between visceral adiposity/IR and the complication of POAF after OPCABG has not yet been clearly established.

The regional distribution of visceral adiposity can be accurately quantified by computed tomography (CT) imaging, which is considered to be the gold standard for measuring visceral adiposity and is termed the CT-based visceral adipose tissue index (VATI) [16]. The triglyceride-glucose (TyG) index, which has been proposed as the common test for IR assessment, can evaluate the severity of IR by measuring the triglyceride and fasting plasma-glucose levels [17, 18], and is associated with CVD [19, 20]. Accordingly, CT-based VATI and the TyG index may be valuable indicators for new-onset POAF, and the present study was designed to investigate the association of the CT-based VATI and TyG index with the incidence of new-onset atrial fibrillation after OPCABG.

The present study assessed the association of CT-based mid-third lumbar vertebrae VATI, VAI, and TyG index with the development of new-onset POAF in patients after OPCABG. In our analysis we found a 1.0 SD increase in CT-based VATI, VAI, and TyG-index levels was significantly associated with an increased risk of new-onset POAF using a fully adjusted model as both a continuous or categorical variable. The sensitivity analyses conducted also confirmed that the CT-based VATI and TyG index were more independently correlated with new-onset POAF than was VAI.

Visceral adipose tissue is an important component of the body and participates in key pathophysiologic processes of regulating lipid and glucose metabolism, insulin sensitivity, and inflammation [22]. Therefore, exploration of the indexes of adiposity to better target likely indicators of CVD remains clinically significant. Previous studies found that a high level of visceral adiposity, rather than general adiposity, was significantly associated with increased CVD risk [23, 24]. A large prospective study, the Heart Outcomes Prevention Evaluation study, examined the association between MI and BMI, or abdominal obesity indexes, and found that abdominal obesity indexes were independent predictors of CVD death, MI, and total mortality [25]. Rexrode et al. [26] observed that elevated levels of visceral adipose tissue were independently associated with a two-fold increase in CHD risk, even after adjusting for hypertension, diabetes, and high cholesterol. In the INTERHEART study, which enrolled 27,098 participants from 52 countries, visceral adipose tissue was found to be closely correlated with the risk of CHD even after adjusting for other risk factors [27]. However, a crucial index used to represent the visceral adiposity in the INTERHEART study was waist circumference (the ratio of abdominal waist to hip circumference) which is a metric that many view as less persuasive than a CT-based visceral adipose tissue index.

The development of imaging technologies, such as CT, has yielded extraordinary progress in understanding the distribution of adipose tissue. CT can scan the whole body, or specific regions of the body, to generate cross-sectional images and calculate respective cross-sectional areas [22]. Nevertheless, there have been only a few clinical studies conducted concerning the association between CT-based VATI and CVD. In an analysis of the Framingham Heart Study Offspring cohort, Mahabadi et al. [23] observed that visceral abdominal adipose tissue is associated with CVD independent of traditional measures of obesity; however, the association between the CT-based VATI and new-onset POAF was not clearly established. Our data show that VATI is associated with POAF, the fully adjusted HR (95% CI) in tertile group 3 versus tertile group 1 was 2.58 (1.12–3.45), and the AUC of the VATI when added into the original model was 0.897 (p 0.001). We also identified that the cutoff value of the cross-sectional VATI predictive of POAF risk was 51.34. To the best of our knowledge, this is the first report that used CT to determine the association of VATI with POAF after OPCABG. In addition, multivariate adjusted models were performed to control for important confounders and this allowed us to provide more precise estimates of the association between VATI and POAF.

In the present study, we used VAI to further investigate a potential association between visceral adipose tissue and new-onset POAF in patients after OPCABG. We found that the association between VAI and POAF was significant after adjusting for age, sex, BMI, and other variables. The fully adjusted HR (95% CI) of VAI in tertile group 3 versus tertile group 1 was 1.88 (1.21–2.95). Furthermore, VAI had a moderate predictive value for POAF with the AUC of VAI added into the original model calculated to be 0.801 (p = 0.021). Previous studies have found that VAI was significantly correlated with an increased risk of various CVDs. For example, Britton et al. [28] observed that VAI, when compared to BMI and waist circumference, was more predictive of cardiovascular risks in a study conducted on the general population. In addition, Amato et al. [29] reported, based on data from 1498 patients, that VAI was a more sensitive and specific predictor of cardiovascular and cerebrovascular events. In another study encompassing a large sample, the elevated level of VAI was also related to cardiovascular events [30]. However, data concerning the association between VAI and POAF after cardiac surgery are relatively limited with only a single small retrospective study that included 199 patients that had on-pump coronary artery bypass operations. Engin et al. [31] found that a high VAI level was associated with an increased POAF risk. Thus, our findings, when taken together with previous studies, support a close relationship between VAI and POAF in patients undergoing either off-pump or on-pump CABG. Furthermore, results suggest that visceral adipose tissue cannot be overlooked as one of the important determinants of potential illness.

Although the underlying mechanisms by which visceral adipose tissue affects atrial fibrillation have not been fully demonstrated, available studies have determined that visceral fat is closely associated with IR [15]. IR refers to the inability of endogenous insulin to be used for peripheral tissues and dysregulated glucose homeostasis in the body [15]. This may predispose patients to progression of atrial fibrillation by enlarging the left atrial size or by damaging the diastolic function of the left ventricle [32, 33, 34], activating the mitogen-activated protein kinase (MAPK) pathway to induce atrial electrical and structural remodeling [34], and destroying the function of insulin-sensitive glucose transporters [35]. The TyG index has been demonstrated to be a more convenient and valid indicator of IR than the current gold standard established using a hyperinsulinemic-euglycemic clamp because the TyG index is simpler and more cost-effective to calculate [17]. Many studies have indicated that TyG index is positively associated with cardiovascular outcomes in different patient populations [19, 20]. To date, only a limited number of studies investigating the relationship between TyG index and POAF have been performed. An analysis of 549 patients who developed ST-segment elevation MI after percutaneous coronary intervention, indicated that elevated TyG index was associated with an increased risk of new-onset atrial fibrillation [36]. Another small retrospective study, with 409 patients diagnosed with hypertrophic obstructive cardiomyopathy, found that the TyG index was an independent predictor of POAF in patients who had undergone septal myectomy [37]. No previous studies, however, have directly investigated the association between the TyG index and the occurrence of new-onset POAF after OPCABG. In the present study, patients in the highest tertile of the TyG index were more inclined to develop POAF than those in the lowest tertile. In addition, we found that a higher TyG index was an independent risk factor for POAF incidence, and had a moderate predictive value as the AUC of the TyG index, when added into the original model, was calculated as 0.878 (p = 0.005).

Obesity has proven to be one of the important, and modifiable, determinants of CVD and can result in undesired outcomes such as POAF after treatments such as CABG [38]. Therefore, it is clinically important to identify obese patients early who are at risk for new-onset POAF. Doing so will help to ensure that adequate precautions are taken to improve clinical outcomes. BMI is the most commonly used indicator of obesity; however, among cardiovascular risk factors, the usability of BMI is controversial and has led to the so-called “obesity paradox” [27]. Consequently, a growing number of studies indicate that excess central obesity was more useful for the prognosis of CVD and prediction of atrial fibrillation [39]. Furthermore, previous studies demonstrated that IR may play a key role in abnormal lipid deposition [15]. Nevertheless, clinical evidence concerning a potential association between visceral adiposity/IR and the complication of POAF after OPCABG has not yet been clearly established. In light of all available information, the strengths of our study include the fact that this represents the first report exploring the potential association between CT-based VATI and new-onset POAF after OPCABG. In addition, both VAI and TyG index are ideal biochemical indicators well-suited for use in routine clinical practice as these indices enable the convenient identification of patients at high risk of POAF. This study also identified cutoff values for desirable VATI, VAI, and TyG indexes and these values may be useful in predicting risk of POAF by using ROC curve analysis, as well as using the multiple-adjusted spline regression model.

There were several limitations noted in this study. First, this study is a single-center, retrospective study. Future large-scale prospective studies are needed to provide conclusive supporting evidence. Second, owing to a lack of data, we could not proceed with serial measurements of VATI, VAI, and TyG index; therefore, we were unable to investigate the correlation between index changes and POAF. Third, we did not analyze follow-up outcomes and this prevented study of the long-term effects related to VATI, VAI, and TyG index. Moreover, VAI is not a currently recognized definitive diagnostic test and it should be used with other clinical assessments to guide risk identification and treatment strategies.

The findings outlined in the present study suggest that elevated VATI, VAI, and TyG index values are independently associated with new-onset POAF in patients who have undergone OPCABG. Large-scale observational studies are needed to verify the present findings; however, our findings indicate that it is plausible to conclude that VATI, VAI, and TyG index may be useful measurements to use as as risk-stratification tools for patients that have undergone OPCABG.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

XBY, KH: study design and critical revision of the manuscript. ZP, RZ, YXY: management of patient follow-up, data collection. RZ, YXY, XBY, KH: help and advice with biomarker measurements, critical revision of the manuscript. ZP, RZ, YXY: data analysis, statistical workup. ZP: manuscript preparation. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

This study protocol was approved by the ethics committee of Beijing Anzhen Hospital (No. 2018101X) and was in accordance with the Declaration of Helsinki. The need for informed consent was waived due to the retrospective study.

Not applicable.

This research was supported by Beijing Natural Science Foundation (7222049).

The authors declare no conflict of interest.