First in-human mapping of bachmann's bundle during atrial fibrillation

Background Bachmann's bundle (BB) is the main route for sinus rhythm (SR) wavefronts to propagate from the right to the left atrium. The parallel fiber arrangement of BB makes excitation of this structure more susceptible to interruption of the right-to-left excitation. Despite its central role in interatrial conduction, it has never been investigated, whether and if so to which degree, BB is affected by atrial fibrillation (AF)-induced atrial remodeling and which markers best reflect this remodeling. Purpose To investigate the severity of BB remodeling in patients with different AF types. Methods Intraoperative epicardial mapping (192 electrodes; interelectrode distances: 2mm) of BB during 10s of AF was performed in patients with paroxysmal AF (PAF, n=12), persistent AF (PeAF, n=20), and induced AF in patients without AF history (no-AF group, n=30). For each patient, the amount of fractionated potentials, median cycle length (CL) and potential voltages were calculated for BB in total and the left (LBB), middle (MBB), and right (RBB) part separately. Pairwise comparisons were corrected using the Bonferroni method (p-value = 0.05/3). Results Mapping data are summarized in Table 1. A total number of 416,192 potentials were recorded (no-AF: 205,766, PAF: 88,626, PersAF 121,800). Median CL at BB was shorter during PeAF compared to no-AF (171.0ms [156.8-183.0] vs 199.0ms [180.0-250.8];p<0.001). AFCL gradients were not observed in any of the patients. Figure 1 shows the distribution of fractionated potentials (left top panel) and median potential voltage (right top panel) for each patient across the AF groups, along with a representative example patient from each group (bottom panel). Both PAF and PeAF patients exhibited the highest percentage of fractionated potentials in the MBB (respectively 15.2% [7.6-23.0] and 24.6% [17.9-33.2]). The prevalence of fractionated potentials at MBB was higher in the PeAF group compared to the no-AF group (24.6% [17.9-33.2] vs 9.6% [7.0-14.1]; p<0.001), while other regions did not differ significantly. Median potential voltages were lower in all regions for the PeAF group (0.8mV [0.6-1.0]) compared to the no-AF group (1.5mV [1.2-1.9];p<0.001) and lower in LBB compared to PAF patients (0.6mV [0.5-1.2] vs 1.3mV [0.8-1.4];p=0.006). Conclusion Low potential voltage and fractionation at BB increase with AF persistence. Despite patient variability, local morphology parameters are useful to assess the severity of BB remodeling.Table 1Figure 1