Conduction time from left bundle branch pacing to the left ventricular lateral wall in two patients in whom cardiac resynchronization therapy pacemaker was implanted.

The efficacy of left bundle branch pacing (LBBP) as cardiac resynchronization therapy (CRT) has been reported, but LBBP may not always improve conduction disturbance in the left ventricle (LV). To evaluate LV electrical conduction delay during LBBP, we measured conduction time from the pacing at left bundle branch to LV lead sensing (LBBP-LV) in two patients in whom left bundle branch-optimized cardiac resynchronization therapy (LOT-CRT) was attempted. Case 1 was a 77-year-old female with dilated cardiomyopathy (DCM) and left bundle branch block. The QRS duration during LBBP was 160 ms and the interval between the stimulus artifact and peak of the R wave in lead V6 (Stim-V6RWPT) was 74 ms. LBBP-LV at the LV mid-lateral wall and LV mid-posterolateral wall were 112 ms and 102 ms, respectively. Case 2 was a 75-year-old female with DCM and nonspecific intraventricular conduction delay. The QRS duration during LBBP was 156 ms and Stim-V6RWPT was 66 ms. LBBP-LV at the LV mid-anterolateral wall, LV mid-lateral wall, and LV mid-posterolateral wall were 96 ms, 107 ms, and 121 ms, respectively. In conclusion, LBBP-LV at the LV mid-lateral area was relatively long. If LBBP does not improve LV conduction disturbances, LOT-CRT may be more effective. Learning objective: The efficacy of left bundle branch pacing (LBBP) for cardiac resynchronization therapy (CRT) has been reported. However, if the conduction time from pacing to the left ventricular (LV) lateral area during LBBP is long, LBBP may not improve LV conduction disturbance, resulting in ineffective CRT. In such cases, more effective CRT would be expected with LV lead implantation at the area of the LV conduction delay during LBBP.