Glycemia and corrected QT interval prolongation in young type 1 diabetic patients: what is the relation?

The relationship between a prolonged QT interval and an increased risk of sudden death has been extensively explored in familial long QT syndrome, sudden infant death, and ischemic heart disease (1–3). Several recent studies also describe the relation between corrected QT interval (QTc) prolongation, diabetes complications, and an increased mortality in adults (4,5). We recently described QTc prolongation and a larger QT dispersion in a cohort of children and adolescents with type 1 diabetes (6). The influence of changes in glycemia on the length of the QT or QTc remains a controversial issue. Experimental hypoglycemia and, just recently, spontaneous clinical episodes of hypoglycemia proved to lead to QTc lengthening (7–9). There is some evidence that prolonged cardiac repolarization contributes to sudden death associated with nocturnal hypoglycemia in young people with diabetes (10–13). On the other hand, a relation between hyperglycemia and abnormal cardiac repolarization has also been described (14). We therefore simultaneously recorded QT and QTc values using 24-h Holter registration and glucose levels with a continuous glucose monitoring system in children and adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS — Nine children and adolescents with stable type 1 diabetes (five males and four females aged 9–19 years) were prospectively recruited from the patient population that regularly attends the Diabetes Clinic for Children and Adolescents of the Antwerp University Hospital. Diabetes duration varied between 1 and 9 years with a median of 6 years. All of the patients were treated with a basal-bolus insulin regimen with at least four subcutaneous injections daily. Exclusion criteria were the presence of other disorders, medication known to modify QT, obvious clinical complications or signs of persistent microalbuminuria (albumine excretion 15 g/min in an overnight timed urine collection), and neuropathy or proliferative retinopathy. A 24-h electrocardiogram (Dynacord 423; Delmar-Reynolds, Hertford, U.K.) was recorded in each patient, with automatic QT, RR interval, and QTc measurements (QTc QT/ RR). The automatic electrocardiogram analysis provided hourly mean values for heart rate, QT, and QTc together with minimum and maximum values. Simultaneously, interstitial glucose concentrations (IGC) were measured via a subcutaneous abdominal catheter using a continuous glucose monitoring system (CGMS) (Minimed; Medtronic, Minneapolis). This technique provides 12 glucose measurements hourly. The system was calibrated first against standard glucometer values.