Patients operated for tetralogy of Fallot and with non-sustained ventricular tachycardia have reduced heart rate variability

Background: To study heart rate variability (HRV) in patients operated for tetralogy of Fallot (ToF) and to identify any correlation between HRV and ventricular tachycardia (VT). Patients and Methods: We studied HRV in 23 consecutive patients operated for ToF (mean age 14 ± 6.6 years; mean follow-up 10.6 ± 5.2 years). Seven patients had non-sustained VT on Holter monitoring. Two control groups were included: 18 healthy subjects and 15 patients operated for other congenital heart disease. There were no differences in age, age at surgery (in the operated groups), follow-up, and mean heart rate between the three groups. Four time and four frequency domain indices were calculated: mean duration of RR intervals, standard deviation of all RR intervals (SD), square root of the mean squared differences of successive RR intervals (r-MSSD), percent of differences between adjacent RR intervals (pNN50), total power (TP), low frequency (LF), high frequency (HF), and LF/HF ratio. Results: HRV indices were identical in the two control groups but were significantly reduced in patients with ToF. Within the patients who had been operated on for ToF, HRV indices were significantly lower in the seven with non-sustained VT than in those without arrhythmias: SD (95 ± 15 vs. 135 ± 54 ms; p = 0.01), r-MSSD (26 ± 9 vs. 45 ± 20 ms; p = 0.03), pNN50 (4.4 ± 3.4 vs. 16.5 ± 12.5%; p = 0.001) and HF (111 ± 97 vs. 352 ± 291 ms2; p = 0.009). Using stepwise multivariate regression analysis, pNN50, age at surgery, degree of pulmonary regurgitation and higher right/left ventricular ratio were independent predictive variables for VT (p < 0.0001; r2 = 0.85). Conclusions: ToF patients, particularly those with ventricular arrhythmias, have significant impairment of sympatho-vagal balance, characterized by a reduction of vagal drive.