It has been reported that sudden cardiac death can occur in postoperative tetralogy of Fallot (TOF) and this episode is related to the sustained ventricular tachyarrhythmia. However, the connecting mechanism of various clinical features and sudden cardiac death is not defined yet. Based on the reports that sudden cardiac death is related to the alteration of heart rate dynamics in some diseases, investigation of heart rate dynamics in postoperative TOF seems important to reveal the mechanism of sudden cardiac death. This study was done as a part of the project to investigate the alteration of heart rate variability and to identify the factors related to the sudden cardiac death in postoperative TOF.

Among the children with postoperative TOF, 13 asymptomatic children without significant hemodynamic disturbances (Doppler velocity for tricuspid regurgitation 2.5m/sec and mild pulmonary regurgitation) and ventricular arrhythmia were selected (10 boys, 3 girls; mean age, 9 year 3 months; mean duration after operation, 7 years). We evaluated the complexity and periodic dynamics of heart rate (HR) throughout 24 hours in these children and control group (mean age, 8 year 10 months). After examining each ECG data on 24-hour Holter ECG segmented into 1-hour length, we analyzed each HR time series and quantified the overall complexity of each HR time series by its correlation dimension. In addition, the power spectrum of HR and obtained low-frequency component (0.08-0.15Hz) and high-frequency component (0.15-0.4Hz) were calculated.

This study showed that TOF group had lower correlation dimension and a nonlinear characteristics of HR time series than control group (4.055±0.4134 vs. 4.9310±0.2054, p<0.05). However, the difference was not significant in the low- (0.9864±0.5598 vs. 1.5560±0.8325, p<0.05) and high- (1.1168±0.1.1448 vs. 0.9271±0.6528, p<0.05) frequency components.

It can be concluded that HR time series are more regular in postoperative TOF. The result was significant in correlation dimension analysis and not in the frequency domain analysis. Although the meaning of this finding in postoperative TOF is not clear at present, this may suggest the phenomenon related to the sudden cardiac death.