Attention-deficit hyperactivity disorder and cardiac vagal control: a systematic review

Attention-deficit hyperactivity disorder (ADHD) is characterized by behavioural disinhibition, deficient emotional self-regulation, inattention, and hyperactivity. The constellation of deficits found in children with ADHD implicates autonomic dysregulation characterized by deficient control of the heart by parasympathetic influences. While it is generally assumed that autonomic regulation of the heart is impaired during ADHD, the information pertaining to this dysregulation is limited. A systematic review of three databases was conducted between January and March 2012 for peer reviewed publications examining the relationship between cardiac vagal control (CVC) and ADHD without comorbid psychopathology. 19 articles were reviewed with only 6 meeting inclusion criteria. Findings were not unanimous but suggested that children with unmedicated ADHD experienced lower levels of CVC than did healthy controls. It was difficult to evaluate whether children with ADHD exhibited a different pattern of withdrawal and application of CVC than did normal controls. Findings suggested CVC reactivity depended on the task employed but children with ADHD experienced dampened CVC reactivity during tasks that involved self-regulation and emotion regulation. Finally, medication acted to correct the autonomic imbalance experienced by children with ADHD but did not bring this imbalance into normal levels. Given that so few studies were identified, no firm conclusions can be made, and there is a clear need for additional research in this area. Recommendations for future research are discussed.