Cardiac Autonomic Function and Atrial Arrhythmias in Adult Patients With a Univentricular Physiology After Fontan...

Cardiac arrhythmias are frequently encountered in patients with single ventricle physiology palliated by the Fontan circulation. Autonomic dysfunction, an imbalance between sympathetic and parasympathetic systems, is critical in arrhythmogenesis. The relationship between impaired autonomic function, cardiac morphology, ventricular function, and clinical outcomes in adult patients remains poorly defined. This study aims to evaluate cardiac autonomic function using heart rate variability and exercise testing and investigate autonomic factors associated with the prevalence of atrial arrhythmias in adult Fontan patients.

Consecutive adult Fontan patients were included in this single-centre, cross-sectional study. Cardiac autonomic function was assessed using 24-hour ambulatory electrocardiogram recordings and exercise testing. Factors associated with atrial arrhythmias were evaluated.

Fifty-four patients (median age 22 years, 56% female) were included. Paroxysmal atrial arrhythmias were present in 26% of patients and associated with significantly lower heart rate reserve (60 vs 91 beats per minute [bpm], P = 0.004) and chronotropic index (0.46 vs 0.82, P = 0.006) during exercise testing. Independent of β-blocker use, the autonomic function parameters, standard deviation of normal-to-normal intervals and standard deviation of the average normal-to-normal intervals calculated of all 5-minute intervals, were reduced in patients with atrial arrhythmias. Ventricular arrhythmias were less frequently encountered (7%).

Atrial arrhythmias, affecting 26% of this cohort, were associated with reduced heart rate reserve and chronotropic index, partly due to β-blocker use, and decreased standard deviation of normal-to-normal intervals and standard deviation of the average normal-to-normal intervals calculated over 5-minute intervals. This suggests impaired autonomic regulation and adaptability in adult Fontan patients, potentially predisposing to late complications. Addressing autonomic dysfunction may help mitigate arrhythmic risks in this population.