Aims/hypothesis  

It has been postulated that hypoglycaemia-related cardiac dysrhythmia and, in particular, prolonged cardiac repolarisation, may contribute to increased mortality rates in children and adolescents with type 1 diabetes.

Methods  

We examined the prevalence of prolonged QT interval on ECG during spontaneous hypoglycaemia in 44 type 1 diabetic subjects (aged 7–18 years), and explored the relationships between serial overnight measurements of QT interval corrected for heart rate (QTc) and serum glucose, potassium and epinephrine levels. Each subject underwent two overnight profiles; blood was sampled every 15 min for glucose measurements and hourly for potassium and epinephrine. Serial ECGs recorded half-hourly between 23.00 and 07.00 hours were available on 74 nights: 29 with spontaneous hypoglycaemia (defined as blood glucose <3.5 mmol/l) and 45 without hypoglycaemia.

Results  

Mean overnight QTc was longer in females than in males (412 vs 400 ms, p=0.02), but was not related to age, diabetes duration or HbA₁c. Prolonged QTc (>440 ms) occurred on 20 out of 74 (27%) nights, with no significant differences between male and female subjects, and was more prevalent on nights with hypoglycaemia (13/29, 44%) than on nights without (7/45, 15%, p=0.0008). Potassium levels were lower on nights when hypoglycaemia occurred (minimum potassium 3.4 vs 3.7 mmol/l, p=0.0003) and were inversely correlated with maximum QTc (r=–0.40, p=0.03). In contrast, epinephrine levels were not higher on nights with hypoglycaemia and were not related to QTc.

Conclusions/interpretation  

In young type 1 diabetic subjects, prolonged QTc occurred frequently with spontaneous overnight hypoglycaemia and may be related to insulin-induced hypokalaemia.