Cardiovascular events with poorly controlled HbA1c
Several studies have analysed the relationship between HbA1c levels and
the incidence of cardiovascular events such as peri-operative myocardial
infarction (MI), atrial fibrillation (AF), and low cardiac output
syndrome. The overwhelming body of evidence has demonstrated that HbA1c
level alone cannot be used as a predictor for cardiovascular
events29-33. By contrast, only one study showed a
relationship between HbA1c and cardiovascular event which suggested that
elevated pre-operative HbA1c may be protective for developing AF43. The main outcomes of these studies are summarised
in Table 5.
The largest cohort study which demonstrated that there was no
relationship between HbA1c level and cardiovascular events analysed
outcomes in 1,461 patients undergoing CABG with or without valvular
surgery 35. The study found that there was no
difference in the incidence of cardiovascular events in patients with
HbA1c <6.5% and >6.5%: AF (26.3% vs 26.6%;P= 0.90), acute MI (0.5% vs 0; P= 0.333) and cardiac
tamponade (0 vs 0.2%; P= 0.313). Other studies similarly showed
that there was no significant difference in the incidence of
cardiovascular events between patients with raised HbA1c levels and
those with normal levels38, 40, 44, 45.
Kinoshita et al 43 carried out a retrospective
analysis of 912 patients who underwent isolated CABG. They found that
median HbA1c was significantly lower in patients who developed AF
post-operatively when compared to patients who did not ((5.8%, 95 %
CI, 5.4-6.3) vs 6.1%, 95% CI, 5.5-7.2); P= 0.01). Additionally,
results also showed that the incidence of post-operative AF showed a
stepwise trend where the incidence decreased as HbA1c level decreased:
28.3% incidence for patients with HbA1c ≤5.6%, 17.4% for HbA1c
5.7-6.7% and 12.5% for HbA1c 6.8-11.4% (P= 0.01). These
findings suggest that high HbA1c levels may be associated with a lower
risk of post-operative AF but this is a single retrospective study
carried out on Japanese patients thereby limiting the generality of
findings and cannot be used as a sole evidence to support this clinical
outcome in general population.