Is there a role for HbAlc in predicting mortality and morbidity outcomes after coronary artery bypass graft surgery?

Abstract

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was is there a role for HbAlc in predicting morbidity and mortality outcomes after coronary artery bypass surgery? Eleven studies presented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The studies presented analyse the relationship between preoperative HbAlc levels and postoperative outcomes following coronary artery bypass graft (CABG) in diabetic, non-diabetic or mixed patient groups. Four studies found significant increases in early and late mortality at higher HbAl c levels, regardless of a preoperative diagnosis of diabetes. One study demonstrated that 30-day survival outcomes were significantly worse in patients with previously undiagnosed diabetes and elevated HbAlc compared with those with good control [HbAl c > 6%; odds ratio 1.53, confidence interval (CI) (1.24-1.91); P = 0.0005]. However, four studies of early mortality outcomes in diabetic patients only showed no significant differences between patients with normal and those with deranged HbAlc levels (P= 0.99). There were mixed reports on morbidity outcomes. Three studies identified a significant increase in infectious complications in patients with poorly controlled HbAlc, two of which were irrespective of previous diabetic status [deep sternal wound infection (P = 0.014); superficial sternal wound infection (P = 0.007) and minor infections (P = 0.006) in poorly controlled diabetics only]. Four studies presented outcomes for total length of stay (LOS). Three of these papers looked specifically at diabetic patients, of which two found no significant differences in length of stay between good and poor preoperative glycaemic control [LOS: P= 0.59 and 0.86 vs P < 0.001]. However, elevated HbAlc vs normal HbAlc was associated with prolonged stay in hospital and in intensive care unit (ICU) in patients irrespective of previous diabetic status [total LOS (P< 0.001)]. Elevated HbAlc levels were also a significant predictor of reduced intraoperative insulin sensitivity in diabetic patients (R =-0.527; P< 0.001). Furthermore, higher HbAlc levels were associated with a reduced incidence of postoperative atrial fibrillation (P = 0.001). We conclude that elevated HbA1 c is a strong predictor of mortality and morbidity irrespective of previous diabetic status. In particular, the mortality risk for CABG is quadrupled at HbAl c levels > 8.6%. Some studies have called into question the predictive value of HbAl c on short-term outcomes in well-controlled diabetics; however, long-term outcomes in this population have not been reported.