Normalisation of blood glucose levels following myocardial infarction predicts favourable in hospital outcome.

Despite a strong association between elevated blood glucose levels and increased rates of mortality among patients hospitalised with acute myocardial infarction (AMI), the benefit of acutely lowering levels of blood glucose remains controversial. Several questions remain unanswered:

(1) Does normalisation of admission hyperglycaemia improved outcome?

(2) What level of blood glucose is associated with lowest mortality?

(3) Do outcomes differ between patients who spontaneously achieve normalisation of glucose levels as compared to those who require insulin?

In order to address these questions Kosiborod et al retrospectively analyzed data from 7820 hyperglycaemic patients hospitalised for biomarker-confirmed AMI, using a database which received patient data from 40 hospitals across the US over a 6 year period (Jan 2000-Dec 2005). Measurements of blood glucose were divided into 5 levels as shown in the table below. Admission blood glucose level was defined as the initial blood glucose level, and postadmission blood glucose level was defined as the mean of all glucose levels obtained after the initial measurement. Patients with admission glucose levels <7.8 were excluded from the analysis. Outcome was defined as all cause in hospital mortality.

Patients with higher postadmission glucose levels had a higher incidence of heart failure (p<0.001) and diabetes (p<0.001) as compared to those with lower postadmission glucose levels. Furthermore these patients were less like to receive percutaneous intervention, had worse renal function, higher leukocyte count, were less frequently treated with antiplatelet drugs (including aspirin) and experienced longer hospital stays. Lower postadmission glucose levels were associated with better in hospital survival both in unadjusted and multivariate adjusted analyses (see table).

Mean postadmission blood glucose level (mmol/L)

Unadjusted analysis

(incidence of in hospital mortality)

Multivariate adjustment

(OR [95% CI] for in hospital mortality)

<6.1

3.1%

No data

6.1 to <7.8

5.7%

2.1 [1.3 – 3.5]

7.8 to <9.4

10.8%

5.3 [3.0 – 8.6]

9.4 to <11.1

11.6%

6.9 [4.1 – 11.4]

>11.1

19.6%

13.0 [8.0 – 21.3]

Lowest mortality was observed among patients with a postadmission glucose level of 4.4 – 7.2mmol/L. Interestingly, following multivariate adjustment admission glucose level failed to predict in hospital mortality (p=0.89) whereas postadmission glucose level remained a robust predictor (p<0.001). Propensity matching failed to demonstrate a difference in outcome among patients treated with insulin and those who were not.

Conclusion:

Glycaemic control, rather than insulin use, appears to be the important factor following AMI. However these results should be interpreted with caution as normalisation of glycaemia may simply represent a surrogate marker of healthy physiology and a recovery from the stress of AMI rather than identify a causal mechanism.

· Kosiborod M, Inzucchi S, Krumholz H et al. Glucose normalization and outcomes in patients with acute myocardial infarction. Arch Intern Med 2009;169(5):438-46