Background: Bachmann's bundle (BB) may potentially play a role in the earlier onset and faster progression of atrial fibrillation in adult patients with congenital heart disease (CHD). It is unknown whether electrophysiological alterations already exist at BB in pediatric patients with CHD and whether they are related to aging. Objective: This study aimed to investigate BB electrophysiology in pediatric patients with CHD and assess the impact of age on BB electrophysiology. Methods: BB mapping was conducted in 55 patients (0.2–17.5 years). Activation patterns, potential voltages, low-voltage areas (LVAs), potential morphology, and conduction disorders of BB were analyzed and correlated with age. Results: Right-to-left activation across BB occurred in 96.4% of patients. Potential voltage was on average 7.2 ± 3.0 mV, and LVAs occurred in 85.4% of patients. Median local conduction velocity was 96.6 (72.9–121.0) cm/s, and conduction block occurred in 56.4% of patients. Most potentials were single and short-double potentials; long-double and fractionated potentials were recorded in 49.1% and 72.7% of patients, respectively. Age was weakly correlated with potential voltages (r = 0.312, P = .020) and moderately with local conduction velocity (r = 0.439, P < .001), but not with potential morphology or conduction block. Conclusion: In pediatric patients with CHD, BB already contains a considerable amount of conduction disorders, LVAs, and potentials with complex morphology. The prevalence of these early electrophysiological alterations is not age related and does not differ among the right, left, and middle parts of BB.

(1) Background: Structural remodeling plays an important role in the pathophysiology of atrial fibrillation (AF). It is likely that structural remodeling occurs transmurally, giving rise to electrical endo-epicardial asynchrony (EEA). Recent studies have suggested that areas of EEA may be suitable targets for ablation therapy of AF. We hypothesized that the degree of EEA is more pronounced in areas of transmural conduction block (T-CB) than single-sided CB (SS-CB). This study examined the degree to which SS-CB and T-CB enhance EEA and which specific unipolar potential morphology parameters are predictive for SS-CB or T-CB. (2) Methods: Simultaneous endo-epicardial mapping in the human right atrium was performed in 86 patients. Potential morphology parameters included unipolar potential voltages, low-voltage areas, potential complexity (long double and fractionated potentials: LDPs and FPs), and the duration of fractionation. (3) Results: EEA was mostly affected by the presence of T-CB areas. Lower potential voltages and more LDPs and FPs were observed in T-CB areas compared to SS-CB areas. (4) Conclusion: Areas of T-CB could be most accurately predicted by combining epicardial unipolar potential morphology parameters, including voltages, fractionation, and fractionation duration (AUC = 0.91). If transmural areas of CB indeed play a pivotal role in the pathophysiology of AF, they could theoretically be used as target sites for ablation.