2:1 Intrahisian block with Wenckebach phenomenon during his bundle pacing.

Background: Intrahisian blocks with split His bundle (HB) potentials are occasionally observed in practice with intrahisian Wenckebach phenomenon being rare. Case presentation: We report a case of an 85c and third-degree atrioventricular block. Some electrophysiological phenomena were recorded which serve as evidence of second-degree block intrahisian within the HB. During HB pacing (HBP) lead deployment, widening and splitting of HB potential and intrahisian Wenckebach phenomenon were recorded in intracardiac electrogram. Then, we began unipolar HBP at 2 V/0.5 ms. The paced QRS exhibited morphology identical to that during intrinsic rhythm, indicating selective capture of the HB. Notably, pacing the H1 potential at 750 ms results in 2:1 intrahisian block with intrahisian Wenckebach phenomenon.

Conclusion: The case highlights the interesting finding of second-degree block intrahisian block in the HBP.