The V6 RWPT is usually stable during transition from ns-LBBP to sel-LBBP. However, it obviously prolongs in this case.

During transseptal lead placement we observe  direct transition from LVSP to sel-LBBP instead from LVSP to ns-LBBP and then to sel- LBBP.

It is difficult to achieve sel-LBBP in the pacemaker mode because of near threshold output of the myocardial and LBB.

It was shown that V6 R-wave peak time (V6 RWPT) prolongs with transition form non-selective left bundle branch pacing (ns-LBBP) to left ventricular septal pacing (LVSP) but remains constant or slightly prolongs with transition to selective left bundle branch pacing (sel-LBBP) [1,2]. Here, we report on a patient who was observed with a LBB potential, isoelectric interval, where the V6 RWPT substantially prolonged with transition from ns-LBBP to sel-LBBP at near threshold output.

Conduction delay

Left bundle branch pacing

Isoelectric interval

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