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

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

DESIGN: Single-centre, prospective observational study. 

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

MAIN OUTCOME MEASURES: 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. 

RESULTS: 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. 

CONCLUSIONS: 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.