Autonomic Cardiac Regulation During Spontaneous Nocturnal Hypoglycemia In Children With Type 1 Diabetes

Background Hypoglycemia is the most common complication in insulin treated diabetes. Though mostly mild, it can be fatal in rare cases: It is hypothesized that hypoglycemia related QTc prolongation contributes to cardiac arrhythmia. Objective To evaluate influence of nocturnal hypoglycemia on QTc and heart rate variability (HRV) in children with T1D. Methods Children and adolescents with T1D for at least 6 months participated in an observational study using continuous glucose monitoring (CGM) and Holter electrocardiogram for five consecutive nights. Mean QTc was calculated for episodes of nocturnal hypoglycemia (<3.7 mmol/L) and compared to periods of the same duration preceding hypoglycemia. HRV (RMSSD, low and high frequency power LF and HF) was analyzed for different 15 min intervals: before hypoglycemia, onset of hypoglycemia, before/after nadir, end of hypoglycemia and after hypoglycemia. Results Mean QTc during hypoglycemia was significantly longer compared to euglycemia (412 +/- 15 vs. 405 +/- 18 ms, p = 0.005). HRV changed significantly: RMSSD (from 88 +/- 57 to 73 +/- 43 ms) and HF (from 54 +/- 17 to 47 +/- 17nu) decreased from before hypoglycemia to after nadir, while heart rate (from 69 +/- 9 to 72 +/- 12 bpm) and LF (from 44 +/- 17 to 52 +/- 21 nu) increased (p = 0.04). Conclusion A QTc lengthening effect of nocturnal hypoglycemia in children with T1D was documented. HRV changes occurred even before detection of nocturnal hypoglycemia by CGM, which may be useful for hypoglycemia prediction.