Changes in the cardiac autonomic regulation in children with attention deficit hyperactivity disorder (ADHD)

ADHD is one of the most common mental disorders among children. We hypothesized that ADHD is associated with the impairment of the cardiac autonomic regulation. The aim of this study was to evaluate the cardiac autonomic regulation in children with ADHD at the rest and during orthostasis using short-term heart rate variability (HRV) analysis.

Eighteen children with ADHD admitted to the Department of Children and Adolescent Psychiatry, Clinic of Psychiatry, University Hospital in Martin, Slovak Republic between January and September 2006 and 18 matched healthy subjects were recruited. HRV analysis was carried out in three positions: supine (S1)-orthostasis (O)-supine (S2). Evaluated parameters were: the mean R-R interval, mean squared successive difference (MSSD), spectral powers in low (LF) and high frequency (HF) bands, total power (TP), coefficients of component variance (CCV LF, CCV HF), LF/HF ratio.

The mean R-R interval was significantly shorter in ADHD group compared to controls in all positions (P<0.05, P<0.001). S1: The parameters MSSD, CCV HF, logHFpower were significantly lower (P<0.05, P<0.05, P<0.01) and ratio LF/HF was significantly higher (P<0.05) in ADHD group compared to controls. O: The parameters MSSD, CCVHF, logHFpower, logTP were significantly lower in ADHD group compared to controls (P<0.01, P<0.05, P<0.01, P<0.01). S2: The parameters MSSD and logHFpower were significantly lower in children with ADHD compared to controls (P<0.05).

The children with ADHD had decreased cardiac vagal modulation and tachycardia in supine positions with altered ability of dynamic activation of the autonomic nervous system in response to orthostasis indicating changes in the cardiac autonomic regulation. Further studies need to be done on a larger sample to confirm these findings and to understand the underlying mechanisms.