Background: Atrioventricular nodal reentrant tachycardia (AVNRT) is typically treated via slow pathway ablation. However, when the circuit involves atypical superior insertions or mid-septal anatomy, the risk of atrioventricular (AV) block increases. Precise differentiation between near-field and far-field His-bundle potentials is crucial to ensure a safe ablation margin. Methods: We report a case of a 19-year-old patient with highly inducible AVNRT. Conventional ablation at the anatomical slow pathway area and coronary sinus ostium failed to eliminate the arrhythmia. Mapping revealed a signal resembling a His-bundle potential at a mid-septal site, 1 cm inferior to the documented His position. To characterize this signal, high-output pacing (10.0 mA) was performed from the ablation catheter to differentiate myocardial capture from selective His-bundle capture by analyzing QRS morphology and stimulus-to-ventricular latency. Results: High-output pacing identified the signal as a "far-field" His potential. Radiofrequency delivery at this site immediately induced sustained junctional rhythms without AV conduction impairment. Post-ablation testing confirmed non-inducibility of the tachycardia, a persistent AH jump with only one echo beat, and preserved AV conduction (final AH 70 ms, HV 30 ms). No complications occurred. Conclusion: In cases where conventional anatomical approaches are ineffective, high-output para-Hisian pacing allows for the safe identification of atypical slow pathway insertion sites. This maneuver effectively differentiates near-field from far-field His signals, minimizing the risk of permanent AV block.
Córdoba-Alvarado et al. (Fri,) studied this question.