Background
Abnormalities in heart rate variability (HRV) have been associated with increased morbidity and mortality. Adults with a history of successful correction of atrial septal defects (ASDs) and ventricular septal defects (VSDs) have clinically relevant abnormalities in HRV. The etiology of these abnormalities is unknown as is when they occur in the natural history of these lesions. We sought to determine whether the abnormalities described in adult patients are identifiable in pediatric patients.

Materials and methods
Eighty-five ASD patients, 105 VSD patients, and 142 non-cardiac surgical comparison patients aged 0–18 years were studied during post-operative admission to the critical care unit using continuously monitored bedside electrocardiographic (ECG) data.

Results
ASD and VSD patients had statistically significantly lower time-domain heart rate variability parameters, i.e., standard deviation of NN interval duration, and lower frequency-domain heart rate variability parameters, i.e., power in the high frequency band and power in the low frequency band, compared to the comparison cohort. The lower frequency band to high frequency band power ratio was lower in ASD patients and higher in VSD patients compared to the comparison cohort. The abnormalities identified correlate well with patterns described in adult patients.

Conclusion
Post-surgical ASD and VSD patients have markedly abnormal heart rate variability patterns indicative of reduced parasympathetic activity and predominance of sympathetic activity. The HRV abnormalities described in adult patients are identifiable as early as the postoperative period in childhood. This finding warrants prospective study to identify drivers of this phenomenon.