Sustained heart rate‐corrected QT prolongation during recovery from hypoglycaemia in people with type 1 diabetes, independently of recovery to hyperglycaemia or euglycaemia

Aim To investigate changes in cardiac repolarization abnormalities (heart rate‐corrected QT [QTc] [primary endpoint], T‐wave abnormalities) and heart‐rate variability measures in people with type 1 diabetes during insulin‐induced hypoglycaemia followed by recovery hyperglycaemia versus euglycaemia. Methods In a randomized crossover study, 24 individuals with type 1 diabetes underwent two experimental clamps with three steady‐state phases during electrocardiographic monitoring: (1) a 45‐minute euglycaemic phase (5‐8 mmol/L), (2) a 60‐minute insulin‐induced hypoglycaemic phase (2.5 mmol/L), and (3) 60‐minute recovery in either hyperglycaemia (20 mmol/L) or euglycaemia (5‐8 mmol/L). Results All measured markers of arrhythmic risk indicated increased risk during hypoglycaemia. These findings were accompanied by a decrease in vagal tone during both hyperglycaemia and euglycaemia clamps. Compared with baseline, the QTc interval increased during hypoglycaemia, and 63% of the participants exhibited a peak QTc of more than 500 ms. The prolonged QTc interval was sustained during both recovery phases with no difference between recovery hyperglycaemia versus euglycaemia. During recovery, no change from baseline was observed in heart‐rate variability measures. Conclusions In people with type 1 diabetes, insulin‐induced hypoglycaemia prolongs cardiac repolarization, which is sustained during a 60‐minute recovery period independently of recovery to hyperglycaemia or euglycaemia. Thus, vulnerability to serious cardiac arrhythmias and sudden cardiac death may extend beyond a hypoglycaemic event, regardless of hyperglycaemic or euglycaemic recovery.