Background: Atrial tachyarrhythmia is a common cause of morbidity and mortality in patients with univentricular physiology undergoing the Fontan operation. We examined cardiac autonomic nervous activity, a predictor of arrhythmia and sudden death in other cardiovascular disease, in patients late after the Fontan operation, employing heart rate variability (HRV) and baroreflex sensitivity.
Methods and results: We measured HRV and baroreflex sensitivity in 22 consecutive patients (8 male, age 26+/-9 years) who had undergone the Fontan operation 13+/-6 years previously, and 22 age- and sex-matched healthy controls. Fontan patients had significantly lower HRV (P<0.0001). Baroreflex sensitivity was measured by the alpha-index method (square root of ratio of RR interval spectral power to systolic blood pressure (SBP) spectral power, in the LF and the HF band) and was also significantly depressed in the Fontan group (P<0.0001 for both). Both low frequency (LF) and high frequency (HF) components of HRV were reduced in the Fontan patients (P<0.0001), but there was interindividual variation so that the LF/(LF+HF) ratio may be high, normal, or low, and decreased with increasing right atrial dimensions (r=-0.62, P=0.006). Patients with a history of sustained atrial arrhythmia had a stronger baroreflex than those without (P=0.005).
Conclusions: Autonomic nervous control of the heart is markedly deranged in patients late after the Fontan operation, with reduced HRV and baroreflex sensitivity. A relative suppression of the sympathetic-compared with the parasympathetic-system was observed in patients with marked right atrial dilation within the Fontan group. Furthermore, stronger baroreflexes were seen in Fontan patients in association with a higher incidence of sustained atrial tachyarrhythmia, implying that sinus node dysfunction is unlikely to be the dominant mechanism. Additional studies are clearly required to examine the prognostic importance of impaired BRS and HRV in these patients.