Cardiac arrhythmias and electrophysiologic responses during spontaneous hyperglycaemia in adults with type 1 diabetes mellitus

•Spontaneous hyperglycaemia didn’t prolong QTc interval in people with T1DM and without history of cardiovascular disease.•Cardiac arrhythmias were uncommon and confined to bradycardia and ectopic beats.•There was considerable diurnal and inter-subject variability in the incidences of arrhythmias.•Reassuringly, hyperglycaemia wasn’t linked with clinically relevant arrhythmias. We examined the effect of spontaneous hyperglycaemia in adults with type 1 diabetes mellitus (T1DM) and without history of cardiovascular disease on heart rate variability (HRV), cardiac repolarisation and incidence of cardiac arrhythmias. Thirty-seven individuals with T1DM (age 17–50 years, 19 males, mean duration of diabetes 19.3 SD(9.6) years) underwent 96 h of simultaneous ambulatory 12-lead Holter ECG and blinded continuous interstitial glucose (IG) monitoring (CGM). HRV, QT interval and cardiac repolarisation were assessed during hyperglycaemia (IG ≥ 15 mmol/l) and compared with matched euglycaemia (IG 5−10 mmol/l) on a different day, separately during the day and night. Rates of arrhythmias were assessed by calculating incidence rate differences. Simultaneous ECG and CGM data were recorded for 2395 hours. During daytime hyperglycaemia vs euglycaemia the mean QTc interval duration was 404 SD(21)ms vs 407 SD(20)ms, P = 0.263. T-peak to T-end interval duration corrected for heart rate (TpTendc) shortened: 74.8 SD(16.1)ms vs 79.0 SD(14.8)ms, P = 0.033 and T-wave symmetry increased: 1.62 SD(0.33) vs 1.50 SD(0.39), P = 0.02. During night-time hyperglycaemia vs euglycaemia, the mean QTc interval duration was 401 SD(26)ms vs 404 SD(27)ms, P = 0.13 and TpTend shortened: 62.4 SD(12.0)ms vs 67.1 SD(11.8)ms, P = 0.003. The number of cardiac arrhythmias was low and confined to bradycardia and isolated ectopic beats. A considerable inter-subject and diurnal variability was observed. Hyperglycaemia in individuals with T1DM without known cardiovascular disease was not associated with clinically important cardiac arrhythmias.