title: QT interval, corrected for heart rate, is associated with HbA1c concentration and autonomic function in diabetes.
abstract: To examine QT intervals corrected for heart rate (QTc) in adolescents with Type 1 diabetes compared with control subjects, and to determine associations with metabolic control and autonomic function.
  
  
  
  Resting electrocardiogram recordings of 142 adolescents with Type 1 diabetes [mean (sd) age 15.3 (2.0) years, diabetes duration 9.0 (3.5) years, HbA1c 71 (17) mmol/mol or 8.7 (1.6)%] and 125 control subjects [mean (sd) age 15.7 (2.5) years] were used to calculate QTc duration and derive mean heart rate and heart rate variability (HRV) values. Linear and logistic regression models were used to examine the associations between QTc, metabolic control and autonomic function (HRV and pupillary function).
  
  
  
  QTc duration was not significantly different between subjects with Type 1 diabetes and control subjects (mean duration 392 vs 391 ms; P = 0.65). In the Type 1 diabetes group, QTc was positively associated with HbA1c [β = 4 (95% CI 2, 6); P < 0.001] and inversely associated with severe hypoglycaemic events [β = -10 (95% CI -20,-2); P = 0.01], less insulin/kg [β = -12 (95% CI -22, -2); P = 0.024] and less HRV. In the Type 1 diabetes group, QTc in the highest quintile (≥409 ms) vs quintiles 1-4 had more pupillary abnormalities (83 vs 56%; P = 0.03), lower pupillary maximum constriction velocity (4.8 vs 5.3 mm/s; P = 0.04), higher heart rate (78 vs 72 beats per min; P = 0.02) and lower HRV (standard deviation of mean NN intervals 4.0 vs 4.3 ms, P = 0.004 and root-mean-square difference of successive NN intervals 3.7 vs 4.1 ms; P = 0.004).
  
  
  
  Although there are concerns about hypoglycaemia in general in people with Type 1 diabetes, chronic hyperglycaemia, rather than intermittent hypoglycaemia, appears to be more deleterious to autonomic cardiac function, even in adolescence. Longer QTc was associated with higher HbA1c concentration, lower risk of hypoglycaemia and autonomic dysfunction. Longitudinal studies are warranted.
authors.affiliation: Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Stern
authors.affiliation: Children's Hospital at Westmead, Institute of Endocrinology and Diabetes, Sydney, Australia.|Discipline of Paediatrics and Child Health, University of Sydney, Sydney, Australia.
authors.forename: Y H
authors.initials: YH
authors.lastname: Cho
authors.affiliation: Children's Hospital at Westmead, Institute of Endocrinology and Diabetes, Sydney, Australia.|Discipline of Paediatrics and Child Health, University of Sydney, Sydney, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Benitez-Aguirre
authors.affiliation: National Health and Medical Research Council, Clinical Trials Centre, Sydney, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Jenkins
authors.affiliation: Department of Endocrinology, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: M
authors.initials: M
authors.lastname: McGill
authors.affiliation: Centre for Vision Research, Westmead Millennium Institute, Sydney, Australia.|Department of Ophthalmology, University of Sydney, Sydney, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Mitchell
authors.affiliation: National Health and Medical Research Council, Clinical Trials Centre, Sydney, Australia.|Department of Cardiology, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: A C
authors.initials: AC
authors.lastname: Keech
authors.affiliation: Children's Hospital at Westmead, Institute of Endocrinology and Diabetes, Sydney, Australia. kim.donaghue@health.nsw.gov.au.|Discipline of Paediatrics and Child Health, University of Sydney, Sydney, Australia. kim.donaghue@health.nsw.gov.au.
authors.forename: K C
authors.initials: KC
authors.lastname: Donaghue
mesh_terms: D000293:Adolescent; D001341:Autonomic Nervous System / Q000502:physiology*; D001342:Autonomic Nervous System Diseases / Q000209:etiology / Q000503:physiopathology; D016022:Case-Control Studies; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000150:complications / Q000503:physiopathology*; D003925:Diabetic Angiopathies / Q000503:physiopathology; D003929:Diabetic Neuropathies / Q000209:etiology / Q000503:physiopathology; D004562:Electrocardiography; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male
chemical_list: D006442:Glycated Hemoglobin