INTRODUCTION

Coronary artery bypass grafting (CABG) surgery and percutaneous coronary intervention (PCI) are widely used revascularization strategies for coronary artery disease (CAD) which reduce mortality and improve quality of life^[1]. Recent data suggested the superiority of CABG in preventing major cardiac events in patients with multivessel disease, particularly in patients with complex CAD and diabetes^[2].

The European System for Cardiac Operative Risk Evaluation (EuroSCORE) and the Society of Thoracic Surgeons (STS) 2008 Cardiac Surgery Risk Model are the most commonly used risk prediction models for cardiac surgery. These scoring systems are not only useful to assess the effect of specific clinical parameters on surgical outcomes, but also to aid in treatment selection, patient counseling, comparison of postoperative results, and quality improvement^[3]. Besides, current mortality risk prediction models for CABG do not have a standardized approach in terms of both defining predictor variables and outcome. In addition, some problematic topics such as inadequate sample size, inappropriate handling of missing data, as well as suboptimal statistical techniques make these risk models debatable^[4]. Need for calculator or computer make these models impractical for daily clinical use. Therefore, more practical risk modeling systems which predict morbidity and mortality are required.

CHADS₂ and CHA₂DS₂-VASc scores are well-validated and proposed scoring systems to establish the risk of stroke in patients with non-valvular atrial fibrillation (AF). Additionally, CHA₂DS₂-VASc score components, such as age, hypertension, diabetes mellitus (DM), and prior cardiovascular event, are also traditional risk factors for CAD. Previous studies demonstrated the association between the CHA₂DS₂-VASc score and the severity of CAD^[5]. Recent studies demonstrated the prognostic value of the CHA₂DS₂-VASc score in patients suffering from acute coronary syndrome (ACS)^[6].

Although CHA₂DS₂-VASc score is proposed as a predictor for immediate and late stroke after CABG, there is no data evaluating the prognostic value of CHA₂DS₂-VASc score in patients undergoing isolated CABG surgery^[7]. When compared with the aforementioned risk models, the CHA₂DS₂-VASc score is a fast and simple method for risk evaluation that requires no calculator or computers. We sought for the prognostic value of CHA₂DS₂-VASc score in individuals undergoing isolated CABG surgery.

METHODS

RESULTS

Four hundred sixty-four patients who underwent elective isolated CABG surgery were included in the study. Patients were dichotomized depending on their CHA₂DS₂-VASc score. L and H score groups were compared as previously described. The L group included 238 patients (median age: 57 years [interquartile range {IQR}: 52-63]; 44 [18.5%] females) while the H group included 226 patients (median age: 64 years [IQR: 55-67]; 45 [19.9%] females). Hypertension, DM, and peripheral vascular disease (PVD) were more frequent in the H group (P<0.001, P<0.001, P=0.044, respectively) than in the L group. EuroSCORE I was similar in both groups (P=0.53). Anatomical based SYNTAX I score was similar in both groups, while clinical SYNTAX II-CABG score was significantly higher in the H group than in the L group (P=0.4, P=0.001, respectively). Postoperative MI was more frequent in the H group (P=0.006) than in the L group. Patients in the H group needed more İAB pump support (P=0.005) than those in the L group. Acute renal failure and mediastinitis in the postoperative period were more frequent in H group (P<0.001, P<0.001, respectively) than in the L group. Clinical, laboratory, and operative parameters were presented in Table 1 and Table 2. The H group had significantly higher in-hospital mortality and MACE rates than the L group (P<0.01).

Table 1 - Demographic, clinical, and laboratory characteristics of the groups.

Table 2 - Operative and postoperative parameters of the groups.

When each component of CHA₂DS₂-VASc score was analyzed in univariate logistic regression analysis, congestive heart failure or ejection fraction < 40%, age, hypertension, PVD, and cerebrovascular event were independent predictors for MACE (Table 3).

Table 3 - Logistic regression of each CHA₂DS₂-Vasc score component for MACE.

We performed univariate analysis including EuroSCORE I, SYNTAX I and SYNTAX II, and CHA₂DS₂-VASc scores. EuroSCORE, SYNTAX II-CABG, and CHA₂DS₂-VASc scores were the predictors for MACE in logistic regression analysis (Hosmer-Lemeshow test, P=0.414, 0.941, and 0.693, and Nagelkerke R Square, P=0.359, 0.047, 0.105; respectively) (Table 4). ROC curve analysis of SYNTAX II-CABG and CHA₂DS₂-VASc scores were performed to predict MACE (Figure 1). SYNTAX II-CABG > 25.1 had 68.4% sensitivity and 52.7% specificity to predict MACE (area under the curve [AUC]: 0.653, P=0.04, 95% confidence interval [CI]: 0.607-0.696). CHA₂DS₂-VASc > 2 had 52.6% sensitivity and 84.1% specificity to predict MACE (AUC: 0.752, P<0.01, 95% CI: 0.710-0.790) (Table 5). We compared CHA₂DS₂-VASc with SYNTAX II-CABG, which is a relatively and comprehensive score. Pairwise comparison of ROC curves revealed the similar statistical accuracy of both scoring systems for prediction of MACE (Z statistic: 1.097, P=0.27) (Figure 2).

Table 4 - Predictors of major adverse cardiac events; univariate logistic regression analysis of CHA₂DS₂-VASc, SYNTAX I, and SYNTAX II scores.

Table 5 - Sensitivity and specifity of CHA₂DS₂-VASc to predict MACE.

Fig. 1 - Receiver-operating characteristic curve analysis of SYNTAX II-CABG and CHA₂DS₂-VASc for prediction of a major adverse cardiac event. AUC=area under the curve; CABG=coronary artery bypass grafting; CI=confidence interval

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Fig. 1 - Receiver-operating characteristic curve analysis of SYNTAX II-CABG and CHA₂DS₂-VASc for prediction of a major adverse cardiac event. AUC=area under the curve; CABG=coronary artery bypass grafting; CI=confidence interval

Fig. 2 - Pairwise comparison of receiver-operating characteristic curves of SYNTAX II-CABG and CHA²DS₂-VASc for prediction of a major adverse cardiac event. CABG=coronary artery bypass grafting; CI=confidence interval; SE=Standard error

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Fig. 2 - Pairwise comparison of receiver-operating characteristic curves of SYNTAX II-CABG and CHA²DS₂-VASc for prediction of a major adverse cardiac event. CABG=coronary artery bypass grafting; CI=confidence interval; SE=Standard error

DISCUSSION

We demonstrated, for the first time, that CHA₂DS₂-VASc score is an independent predictor for MACE in patients undergoing isolated CABG. Although CHA₂DS₂-VASc score includes only clinical parameters, it is as accurate as SYNTAX II-CABG, which includes a detailed angiographic evaluation.

CABG is a safe procedure with low rates of mortality and morbidity. However, the ability to accurately predict adverse outcomes and short- and long-term mortalities after CABG is an important issue that may allow planning preventive strategies and minimize complications^[8]. EuroSCORE, STS risk calculator, and Parsonnet score are the most commonly used risk stratification models which include multiple variables, requiring online calculators for estimation of risk-related mortality and morbidity with CABG^[9]. Nevertheless, these are complex and impractical tools to use at the bedside. Therefore, we still need models to quickly and easily predict risk at bedside, without the need for computational software. In practice, the bedside risk assessment not only provides the surgeon an objective, measurable risk profile to identify patients who require meticulous care, but it also provides the patients a more detailed knowledge of the risk related with the surgical procedure^[10].

CHA₂DS₂-VASc score is an easily applicable time-saving risk model which predicts the risk of thromboembolic events in patients with non-valvular AF in daily practice. CHA₂DS₂-VASc score components, such as older age, female gender, hypertension, DM, extracardiac arteriopathy, low LVEF, and preoperative stroke, and the presence of CAD were reported as predictors of early outcomes after CABG^[11].

The female sex has been reported as an independent predictor of short- and long-term mortalities and adverse events after CABG^[12]. Although the female sex is included in both STS and EuroSCORE, evidence is controversial. Several studies concluded that the female sex is not a risk factor for post procedural mortality after CABG^[13]. In our study, the female sex was not found to be associated with MACE, which is compatible with previous studies.

Increased age (> 60 years) has been reported as an independent predictor of mortality and adverse events after CABG^[14]. In the EuroSCORE model, 60 years of age was accepted as a cut-off value, thus one point was assigned per each five years above 60 years. In the CHA₂DS₂-VASc score, one point was assigned for 65-75 of age years and two points were assigned for age ≥ 75 years. Compatible with previous studies, our study demonstrated an association between age and MACE^[14].

Heart transplantation (HT) and DM are not included in the EuroSCORE risk model. On the other hand, HT, DM, and age were the predominant variables causing high scores in our study. Age and HT were independent predictors for MACE in the present study. Although several studies revealed that patients with DM are at high risk for MACE and death after CABG, univariate analysis revealed that DM was not an independent predictor for MACE in the present study, like studies by Rajakaruna et al.^[15]. These conflicting data may be related to defining the criteria of DM. DM was defined as the need for insulin or oral medication in the present study, while another study defined DM as the need for diet, oral medication, or insulin therapy^[16]. Patients with insulin-dependent DM have a significantly higher rate of mortality and MACE than those with non-insulin-dependent DM^[17]. We also did not classify DM as insulin-dependent or non-dependent. These might explain the different outcome associated with diabetes on early mortality in the present study.

Although there is conflicting data in the literature, we showed that preexisting HT is a poor predictor for patients undergoing isolated CABG^[18]. CABG has been shown to be superior to medical therapy alone in patients with preoperative low LVEF^[19]. Besides, Dalen et al. showed that the reduced ejection fraction doubled the risk of early postoperative death^[20]. Compatible with the previous studies, patients with left ventricular systolic dysfunction and symptoms of heart failure had significantly high in-hospital mortality and morbidity in our study^[9].

Similar to our study, numerous studies have demonstrated that the PVD was an independent predictor of early mortality and poor short-term outcome after CABG^[21]. On the other hand, the association between PVD and early mortality was not confirmed in some studies^[22].

History of stroke has been found to be associated with mortality and increased early and late postoperative stroke^[23]. In line with the literature, the present study demonstrated that a history of preoperative stroke was associated with poor outcome.

Consequently, when we performed univariate analysis of each CHA₂DS₂-VASc score component, congestive heart failure or ejection fraction < 40%, age, hypertension, cerebrovascular accident, and PVD were significantly associated with MACE in patients undergoing after isolated CABG, whereas DM and sex were not.

Several studies have demonstrated an association between the CHA₂DS₂-VASc score and increased mortality and non-fatal adverse cardiovascular outcomes in different clinical conditions, regardless of the presence of AF^[24]. Recently, Hamid et al. observed high mortality in the patients undergoing transcatheter aortic valve replacement who had CHA₂DS₂-VASc score > 6. Therefore CHA₂DS₂-VASc score was proposed as a simple tool for the identification of high-risk patients for short-term and mid-term mortalities in patients undergoing transcatheter aortic valve replacement (TAVR)^[25].

This the first study which aimed to investigate the value of CHA₂DS₂-VASc score to estimate MACE in patients undergoing isolated CABG surgery. Biancari et al. demonstrated predictive accuracy of CHA₂DS₂-VASc score for immediate and late stroke in patients after CABG without pre- and postoperative AF. They also demonstrated that CHA₂DS₂-VASc score is a predictor for late all-cause mortality and cardiovascular mortality^[8]. But there is no data specifically evaluating the value of CHA₂DS₂-VASc score for prediction of in-hospital mortality and MACE in patients undergoing isolated CABG.

CONCLUSION

We showed that CHA₂DS₂-VASc score may predict in-hospital mortality and MACE in patients undergoing isolated CABG in our study population. CHA₂DS₂-VASc score is a handy risk stratification score and easily appliable at bedside without any computational software. Further studies are required to assess the validity of our findings in larger populations.