HbA1c and Cerebrovascular accident
Cerebrovascular accident (CVA) is a severe complication following CABG surgery. CVA indicates whether a patient had a stroke (acute neurologic deficit lasting more than 24 hours) or a transient ischemic attack (TIA) (deficit resolving within 24 hours). The meta-analysis by Zheng et al. assessed the effect of HbA1c levels and CVA among diabetic patients (n=4356) undergoing CABG surgery 44. Their analysis, which included five studies 20,28,45–47 indicated that HbA1c levels were directly correlated with the risk of stroke after CABG surgery (OR 2.07, 95% CI 1.29–3.32, p  = 0.003), with very low heterogeneity (I 2 = 0%; p  = 0.42). Only one retrospective study significantly indicated a possible role for HbA1c in predicting stroke outcomes20. This retrospective study had a comparatively large sample size (n=3089), hence sufficient power to solely elucidate an association between HbA1c levels and stroke. The study indicated that patients with HbA1c values of 7.6% or more have adjusted odds of CVA 2.23 (1.06-4.70) times higher than patients with values below that threshold. The overall incidence of stroke for all patient was very low (1.7%). Other studies were either contradictory 45,46 or inconclusive28,47 due to small sample sizes and inherent low incidence of stroke.
However, a larger and more recent meta-analysis (n=5,381) conducted by Wang et al. showed that there was no significant difference in stroke incidence between diabetic patients with lower preoperative HbA1c levels and those with higher preoperative HbA1c levels after CABG and PCI (OR 1.49, 95% CI 0.94-2.37, p = 0.37, andI 2 = 8%) 48. Higher HbA1c levels were defined as preoperative HbA1c ≥ 6.5% or 7% and lower HbA1c levels as preoperative HbA1c < 6.5%% or 7%.
Interestingly, Biskupski et al 39 noted that TIAs were more common in patients with HbA1c < 7%, while strokes were significantly more common in patients with decompensated diabetes (HbA1c < 7% vs HbA1c > 8%, p = 0.04). Current research indicates a potential association between the baseline risk of TIA events and exposure to hypoglycaemia49,50.