Evaluation of heart rate variability, QT dispersion, and Tp-e interval in pediatric subclinical hypothyroidism

Clinical effects of subclinical hypothyroidism are not clearly understood. This study aims to investigate the effects of subclinical hypothyroidism (SH) on cardiac autonomic and conduction systems in children.

Forty-seven cases (25 female, 22 male) with SH aged between 3 and 17 years and 46 controls that were age, body mass index and sex matched, were included in the study. Heart rate variability (HRV) was used to evaluate cardiac autonomic function while QT dispersion, P dispersion and Tp-e measurements from ECGs to evaluate susceptibility to arrhythmia.

Standard deviation of the average of Normal-Normal intervals in 5-minute measurements was lower in the SH group compared to controls. No statistically significant differences were found in other time or frequency domain parameters. Maximum and minimum corrected QT intervals were longer in the SH group (p = 0.047 and p = 0.012, respectively); there were no significant differences in other ECG parameters.

Our study demonstrates that cardiac autonomic dysfunction and arrhyhtmogenesis shown as susceptibility to ventricular arrhythmia and longer intraatrial conduction times, appear in children with SH.

To our knowledge, this is the first study to show changes in cardiac autonomic function using heart rate variability in children with subclinical hypothyroidism (SH). We suppose that the fact that ventricular repolarization is longer in children with SH regardless of heart rate shows a predisposition to ventricular arrhythmia. Our study demonstrates that cardiac autonomic dysfunction and arrhythmogenesis shown as susceptibility to ventricular arrhythmia and longer intraatrial conduction times, appear in children with SH. We suggest that an evaluation regarding arrhythymia together with endocrinological follow-up is warranted when children are diagnosed with SH.