The relationship between blood glucose level and QTc duration in the critically ill

To determine whether hyperglycaemia is associated with prolongation of the corrected QT (QTc) interval on the electrocardiogram (ECG) in critically ill patients.

Single-centre, prospective observational study.

197 consecutive patients admitted to the adult intensive care unit of a 570-bed teaching hospital over 10 weeks from November 2004.

Correlation between QT interval (on standard 12-lead ECG taken on ICU admission, corrected with Bazett's formula) and serum glucose level (BGL) in blood collected at time of ECG; comparison of variables, including BGL, by QTc category (< or = 0.44 s or > 0.44 s); explained variance (R(2)) of QTc, determined by multivariate regression analysis.

Mean patient age was 53.4 years. A moderate, positive correlation was found between QTc and BGL (Pearson's correlation coefficient, r = 0.277, P < 0.001). A standard multivariate regression model explained 32.9% (R(2)) of QTc variance, and revealed four significant, independent predictors of QTc duration: heart rate (explaining 11.4% of QTc variance), use of inotropes (10.1%), BGL (7.3%) and serum magnesium level (4.6%). In the cohort with QTc > 0.44 s, BGL was significantly higher, as were the need for inotropes, APACHE II scores and mortality. QTc was significantly longer in patients with BGL > 8 mmol/L than in those with lower BGL (0.471 v 0.442 s, P < 0.001). The only independent predictors of mortality were APACHE II score and mean arterial pressure.

There was a moderate, significant correlation between QTc and BGL. Patients with a QTc > 0.44 s had higher BGL, APACHE II score and mortality. BGL was an independent predictor of QTc duration, but neither BGL nor QTc were independent predictors of mortality in this study.