Changes in cardiac repolarization during clinical episodes of nocturnal hypoglycaemia in adults with Type 1 diabetes

Aims/hypothesis. Experimental hypoglycaemia leads to abnormal cardiac repolarization manifest by a lengthened QT interval and caused by adrenergic stimulation. However it is less clear whether spontaneous clinical episodes lead to similar changes. We have therefore measured cardiac ventricular repolarization and counterregulatory responses in patients with Type 1 diabetes during hypoglycaemic and euglycaemic nights. Methods. We studied 22 patients with Type 1 diabetes (mean age 40.4+/-17.2 years, duration of diabetes 17.2+/-9.3 years, HbA1c 8.2+/-1.2% overnight). Measurements were taken hourly of blood glucose, plasma potassium, catecholamines and high resolution electrocardiograms. Results. Hypoglycaemia (blood glucose level <2.5 mmol/l) occurred on 7 of the 22 nights. During overnight hypoglycaemia, QTc interval increased by 27 ms (+/-15) above baseline, compared with 9 ms (+/-19) during nights with no nocturnal hypoglycaemia (p=0.034, 95%CI 2, 35). Adrenaline increased by 0.33 nmol/l (+/-0.21) above baseline during hypoglycaemia, compared with -0.05 nmol/l (+/-0.08) during euglycaemia (p=0.001, 95%CI 0.19, 0.56 nmol/l). There was no significant difference between potassium, and noradrenaline concentrations between the two groups. Conclusion/interpretation. QTc interval lengthens significantly during spontaneous nocturnal hypoglycaemia. Increases are generally less than those observed during experimental hypoglycaemia and could reflect attenuated sympathoadrenal responses during clinical episodes. The clinical relevance of these changes is uncertain but is consistent with the hypothesis that clinical hypoglycaemia can cause abnormal cardiac repolarization and an attendant risk of cardiac arrhythmia.