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.