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