Discussion:
Left bundle branch pacing is a promising alternative to HBP. Presence of
right bundle branch conduction delay pattern (qR in lead V1) and
demonstration of LB potentials are often used as criteria for LBB
capture2,3. LBB potentials may not be demonstrable in
all patients, especially in those with LBBB. Transition in QRS
morphology from non-selective to selective LB capture or nonselective to
LV septal capture may be noted at near threshold
outputs4. Rapid rotation of the pacing lead is
necessary to achieve deep penetration of the interventricular septum.
Perforation into the LV cavity can occur if the lead is advanced too
rapidly. Premature ventricular complexes are commonly noted while
positioning the lead in the interventricular septum. The PVC morphology
depends on the depth of the lead in the septum. We observed gradual
change in morphology from wide QRS with QS morphology in lead V1 to
narrow QRS with qR pattern in lead V1 as the lead penetrated the septum
from right ventricular side to the LBB area. In all four cases, rapid
rotations were stopped as soon as PVCs with narrow QRS/qR pattern were
observed (VES1, VES2, VES3 and VES4). Paced QRS morphology matched the
PVC morphology with short and constant pLVAT at differential pacing
(high and low output). Though the pacing indications varied in these
patients PVC morphology predicted LB capture and guided in deciding the
lead depth. LBB potentials were noted in two patients (CHB and AVJ
ablation cases). It is possible to record LBB potentials in patients
with LBBB during PVCs of RBB morphology if continuous recording can be
performed during lead rotations. Lack of a revolving connector-pin
during lead rotations is a limitation with the current implant
technique. Further rotations were avoided, preventing perforation of
septum. Monitoring the change in PVC morphology and QRS duration during
lead fixation would help in final positioning of the LBB pacing lead and
confirming conduction system capture.
Since the initial description of LBBP, multiple studies have shown the
safety and efficacy of left bundle branch pacing. Huang et
al5, demonstrated 97% success rate in LBBP for
non-ischemic cardiomyopathy and LBBB along with significant improvement
in LV ejection fraction at 1 year. A large retrospective multicenter
study by Vijayaraman et al6, showed 85% success rate
in achieving cardiac resynchronization therapy by LBBP (277 out of 325
patients). Improvement in LVEF was noted in both ischemic and
non-ischemic cardiomyopathy and similarly in patients with LBBB and
non-LBBB. Conduction system pacing combined with AV node ablation showed
a high success rate in persistent atrial fibrillation patients with
heart failure and ICD indication7. This study also
showed significant improvement in LV function and reduction in
inappropriate shocks.
LBBP is emerging as a promising option to deliver physiological pacing.
Though several criteria have been proposed to confirm capture of left
bundle, prospective studies are necessary to validate. PVC guided lead
placement would help in final positioning of the lead and avoid septal
perforation into LV cavity