Interesting phenomena during threshold testing of conduction system pacing: What is the mechanism?

BACKGROUND

Although the interest in conduction system pacing is increasing, the data on longitudinal dissociation in the literature is still limited. METHODS AND

RESULTS

We performed left bundle branch (LBB) pacing on a patient with sick sinus syndrome and atrioventricular block. The transition of QRS morphology can be observed during the threshold testing. The main findings were different left ventricular activation times when selective LBB capture was performed at different outputs.

CONCLUSIONS

This phenomenon may be due to the anatomical basis of longitudinal dissociation of the His-Purkinje system, which allows pacing stimulation at different thresholds to excite different portions of the conduction system.