Output-dependent electrocardiographic criteria to distinguish Bachmann bundle area pacing from high atrial septal...

Bachmann bundle area pacing (BBAP) improves interatrial synchrony, but its anatomic overlap with high atrial septal pacing (HASP) limits the reliability of fluoroscopy and static electrocardiogram (ECG) criteria for identifying preferential interatrial conduction.

To determine whether output-dependent ECG changes, validated by coronary sinus (CS) mapping of left atrial (LA) activation, can differentiate BBAP from adjacent HASP during implantation.

Fifty-seven patients undergoing attempted BBAP were prospectively studied. Intraprocedural pace mapping with incremental output adjustment was performed before lead fixation. P-wave duration (PWD) and stimulus-to-P-wave peak time in lead II (Stim-PWPT_II) were recorded along with LA activation timing, defined as stimulus-to-distal CS atrial electrogram interval (Stim-CS_d). Output-dependent changes in P-wave morphology and timing were evaluated, and leads were repositioned to achieve shorter PWD and earlier LA activation.

Abrupt output-dependent P-wave morphology transitions were observed in 41 of 57 patients (71.9%). Mapping-guided lead repositioning achieved a final pacing site with physiologic markers consistent with BBAP in 56 of 57 patients (98.2%). Compared with HASP without abrupt transition, BBAP demonstrated shorter PWD, Stim-PWPT_II, and Stim-CS_d intervals (all P < .001). A ΔStim-PWPT_II of ≥10 milliseconds consistently separated the study-defined BBAP and HASP groups within this cohort but should be considered hypothesis-generating and requires prospective validation.

Output-dependent ECG transition, particularly changes in P-wave morphology, Stim-PWPT_II, and CS activation timing, provides practical and reproducible intraprocedural markers of preferential interatrial conduction. These findings represent physiologic evidence rather than definitive proof of direct Bachmann bundle capture.