Prolonged cardiac repolarisation during spontaneous nocturnal hypoglycaemia in children and adolescents with type 1 diabetes.
OBJECTIVE
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 HbA(1)c. 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
In young type 1 diabetic subjects, prolonged QTc occurred frequently with spontaneous overnight hypoglycaemia and may be related to insulin-induced hypokalaemia.
Murphy
N P
NP
Department of Paediatrics, University of Oxford, UK.
Ford-Adams
M E
ME
Ong
K K
KK
Harris
N D
ND
Keane
S M
SM
Davies
C
C
Ireland
R H
RH
MacDonald
I A
IA
Knight
E J
EJ
Edge
J A
JA
Heller
S R
SR
Dunger
D B
DB
D000293:Adolescent; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology*; D001786:Blood Glucose / Q000378:metabolism; D002320:Cardiovascular Physiological Phenomena; D002648:Child; D002940:Circadian Rhythm; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000503:physiopathology*; D004562:Electrocardiography; D004837:Epinephrine / Q000097:blood; D006442:Glycated Hemoglobin / Q000032:analysis; D006339:Heart Rate; D006801:Humans; D007003:Hypoglycemia / Q000503:physiopathology*; D007328:Insulin / Q000097:blood; D011188:Potassium / Q000097:blood; D011627:Puberty
D001786:Blood Glucose; D004837:Epinephrine; D006442:Glycated Hemoglobin; D007328:Insulin; D011188:Potassium