Heart rate variability in pubertal girls with type 1 diabetes: its relationship with glycaemic control, insulin resistance and hyperandrogenism

Objective To examine the association between glycaemic control, insulin resistance and hyperandrogenism on cardiac autonomic function in peripubertal girls with type 1 diabetes. Design Prospective, clinic-based study of 125 girls with diabetes and 46 age-matched nondiabetic girls. Measurements Heart rate variability (HRV) parameters derived from a 10-min ECG recording using LabChart Pro were as follows: standard deviation of mean NN intervals (SDNN), where NN=adjacent QRS complexes; root mean squared difference of successive NN intervals (RMSSD) - estimates of overall HRV; and low-/high-frequency (LF:HF) ratio - an estimate of the sympathovagal balance. Androgens and sex hormone binding globulin (SHBG) were measured in girls with diabetes, and free androgen index (FAI) calculated. HRV and anthropometry were measured in nondiabetic controls. Results Adolescents with diabetes (median age 15 center dot 1years [13 center dot 3-16 center dot 0], diabetes duration 7 center dot 0years [4 center dot 6-10 center dot 0] and median HbA1c 8 center dot 4% [7 center dot 5-9 center dot 3]) had higher HR and lower HRV compared with controls. Using multivariate models in the diabetes group, higher HR was associated with higher HbA1c, total daily dose insulin/kg body weight and systolic BP standard deviation scores (SDS), whilst reduced HRV was associated with higher HbA1c (SDNN, RMSSD and LF:HF ratio), lower SHBG (SDNN and RMSSD) and higher weight SDS (LF:HF ratio). Higher FAI was associated with higher HR and reduced HRV measures in the univariate analyses only. Conclusions In adolescent girls with diabetes, reduced HRV parameters are associated with worse glycaemic control, lower SHBG and higher weight SDS. SHBG should be considered in the cardiac risk models for this population.