Increased QT dispersion during hypoglycaemia in patients with type 2 diabetes mellitus.
OBJECTIVE
To study effects of insulin-induced hypoglycaemia on the cardiac repolarization, using QT interval measurements, in patients with type 2 diabetes.


METHODS
Hypoglycaemia was induced by an i.v. insulin-infusion and blood glucose was clamped at 2.7 mmol L-1 for 60 min (T = 90-150 min) in two experiments, with (+GLIB) and without (-GLIB) glibenclamide. In a third experiment, with similar hyperinsulinaemia, glucose was clamped at a euglycaemic level (;5 mmol L-1). ECG was continuously recorded for arrhythmia-monitoring, and 12-lead ECGs were recorded at T = 0 and 150 min. QT intervals were measured, and we determined QT dispersion (difference between the maximum and the minimum QT interval) reflecting interlead variability of repolarization.


METHODS
Thirteen patients with type 2 diabetes, on combined insulin and glibenclamide treatment, were studied during hypoglycaemia, and eight of them participated in the euglycaemic experiment.


RESULTS
No significant arrhythmias were seen during hypoglycaemia but the mean QT intervals and QT dispersion increased significantly (P < 0.001), with no differences between -GLIB and +GLIB. During the euglycaemic clamp all QT measurements remained unchanged. Serum potassium decreased significantly (P < 0.001) during all three clamps, but the decrease was more pronounced during hypoglycaemia. The change in potassium was not correlated to the degree of QT prolongation or QT dispersion.


CONCLUSIONS
Significant changes in the repolarization of the heart can be seen during hypoglycaemia in patients with type 2 diabetes, indicating an increased risk of arrhythmia at low blood glucose levels.
Landstedt-Hallin
L
L
Division of Internal Medicine, Karolinska Institute, Danderyd Hospital, Sweden. Lena.Landstedt-Hallin@kids.ki.se
Englund
A
A
Adamson
U
U
Lins
P E
PE
D000368:Aged; D001145:Arrhythmias, Cardiac / Q000097:blood / Q000139:chemically induced* / Q000503:physiopathology; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology*; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D015309:Glucose Clamp Technique; D005905:Glyburide / Q000009:adverse effects*; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D007003:Hypoglycemia / Q000097:blood / Q000503:physiopathology*; D007004:Hypoglycemic Agents / Q000009:adverse effects*; D007328:Insulin / Q000008:administration & dosage / Q000097:blood*; D008297:Male; D008875:Middle Aged; D013997:Time Factors
D007004:Hypoglycemic Agents; D007328:Insulin; D005905:Glyburide