Background: Sustained ventricular tachycardia (VT) and sudden cardiac death (SCD) remain devastating late complications after repair of Tetralogy of Fallot (ToF). Although heart rate variability (HRV) and baroreflex sensitivity (BRS) are recognized as independent markers of autonomic activity and strong predictors of SCD in major cardiovascular disease, little is known about their role in patients with tetralogy.
Methods and results: We measured HRV and BRS in 45 ToF patients (27 male, age 35+/-12 years, 26+/-7 years after repair) and 45 matched healthy controls. Subjects underwent 20 minute of resting measurements of heart rate (ECG) and noninvasive beat-to-beat blood pressure recording (Finapres), with 5 minutes of 0.1Hz controlled breathing followed by cardiac MRI. BRS was computed by spectral analysis and the sequence and controlled breathing methods. All HRV time and frequency domain variables were measured. All BRS and HRV variables were significantly reduced in patients compared with controls (P<0.001 in all). HRV tended to increase with years from repair. BRS decreased with previous palliation and increasing patient age. Both HRV and BRS decreased with pulmonary regurgitation, elevated right ventricular end systolic volumes and reduced right and left ventricular ejection fraction. Finally, there was an inverse relation between QRS duration (predictor of sustained VT and SCD) and indices of HRV but no relation with indices of BRS.
Conclusion: There is global impairment of autonomic nervous system regulation late after repair of tetralogy with marked reduction of BRS and HRV. This seems to relate to previous surgical intervention/s, their timing and current right and left-sided hemodynamics. Reduced HRV also related to markers of sustained VT and SCD, suggesting possible common pathogenic mechanisms. Further studies are required to examine the prognostic significance of impaired BRS and HRV in these patients.