MetS increases the risk of developing coronary artery disease (CAD) and is also more prevalent among patients who undergo CABG. MetS has been reported to occur in up to 13% of the general population in China . However, in our study, the prevalence of MetS of 45.8% was consistent with that of previous studies in which MetS and CABG were investigated [5, 12, 18].
Several studies have reported an association between postoperative outcomes and MetS [6, 7, 12, 13, 18]. According to these studies, patients with MetS have increased risks morbidity and mortality after CABG, both overall and from CVD. One of the negative effects of MetS is a change in the structure and function of the left ventricle . As Azevedo et al. found, increased severity of MetS is associated with increasingly compromised structure and function of the heart . Yazicio et al. also reported that more severely impaired LV systolic function after acute MI may contribute to the higher morbidity and mortality observed in patients with MetS . However, whether MetS still has an adverse effect on postoperative prognosis among patients with LV dysfunction who undergo CABG has not been demonstrated. This is the first study to delineate the role of MetS in operative mortality and complications in these patients. In our study, we found that, in line with previous reports, MetS is an important predictor for higher operative morbidity and mortality in CABG patients with impaired LV systolic function.
The components of MetS, such as diabetes, hypertension and obesity, have been reported to be associated with a higher incidence of operative mortality after CABG. When analyzing 41,663 patients with diabetes, Carson JL et al. found increased morbidity and morbidity after CABG in diabetic patients during hospitalization when compared with nondiabetic patients . Despite the lack of convincing evidence in the literature, obesity is often considered to be a significant risk factor for postoperative mortality when selecting candidates for CABG [21,22,23]. Moulton et al. concluded that those with a history of hypertension have an increased frequency of immediate post-operative complications and an increased 2-year mortality after CABG . Aronson S et al. also reported that isolated systolic hypertension is associated with increased perioperative cardiovascular morbidity in coronary artery surgery patients . However, patients with DM, obesity and hypertension did not have increased morbidity and mortality independently in our study. The discordant results may result from disagreement among the criteria adopted or the characteristics of the populations and the methodological strategies used.
We also found the presence of both MetS and DM significantly increased the risk of operative mortality among patients with impaired LV systolic function, whereas patients without MetS were not at higher risk. These results demonstrated that the effect of MetS on operative mortality was not a single effect of DM, but the aggregation of multiple factors, such as hypertension, hyperglycemia, and obesity, which acted as a combined risk factor for operative mortality. The clustering of cardiovascular risk factors in MetS demonstrated that the multiple complex metabolic reactions involved in glycotoxicity, lipotoxicity, altered insulin signaling, increased cytokine activity and interstitial deposition of triacylglycerol may directly or indirectly impact myocardial function, and then reduce survival in MetS patients with LVEF<50%. Moreover, we found that the distributions of the causes of death were similar among patients with or without MetS, and about 40% deaths were of cardiac origin. Regarding postoperative complications, there were differences in the percentages of patients with ventricular fibrillation, septicemia and renal failure after CABG between the two groups.
This study provides further evidence that MetS is a prevalent and important risk factor for operative mortality after CABG in patients with impaired with LV systolic function. Furthermore, the components of MetS have synergistic effect in postoperative mortality among patients with EF<50%. These findings have major clinical implications. For instance, multifactorial intervention in patients with MetS who are referred to CABG is required for improving poor prognosis, including optimal control of lipids, blood pressure, blood glucose and body weight. It should be noted, however, that many patients with MetS are not being treated appropriately . There is a definite need for clinics to focus on developing tools to reduce conditions associated with MetS. These tools include early identification, education, lifestyle modifications, and pharmacological interventions. In addition, the identification of MetS might be helpful for classifying high-risk patients, improving risk stratification for CABG patients and assessing the prognosis of CVD. Further large-scale and long-term studies are needed to determine whether MetS is responsible for the increased mortality after CABG surgery, especially in patients with impaired LV systolic function. Further studies are needed to determine whether perioperative medications might be effective in reducing mortality in MetS patients after CABG surgery. In addition, Further studies are necessary to clarify the mechanisms that the components of MetS work synergistically to increase the risk of operative mortality.
This was a retrospective single-center study on ethnic Chinese patients. Its retrospective nature and the small number of patients limit the validity of the clinical outcome. However, the use of specific statistical evaluations enabled relatively precise risk and outcome assessments and comparisons. Although larger samples would be needed to produce more accurate and convincing results, we believe that our study already presents interesting findings related to postoperative outcomes. In addition, because waist circumference data were not available, we selected a BMI > 25 kg/m2 as the cutoff point for obesity based on the results of a previous study on the relationship between BMI, waist circumference, and obesity in a Chinese population. If waist circumstances had been used to define obesity in the detection of MetS, more specific results might have been obtained.