Role of Left Bundle Branch Pacing: will it replace other pacing
modality for CRT?
LVSP has emerged as an alternative method for delivering physiological
pacing particularly in patients with infranodal atrioventricular block
and left bundle branch block (LBBB). Though HBP can correct classic LBBB
in 97% of patients60, the site of block is often
located within the His or proximal left bundle61. The
proximal left bundle branches run through the LV septum and fan out
proving a wider target for pacing. Huang et al have reported a technique
for left bundle pacing using a transseptal approach62.
Left bundle pacing has been reported to have low pacing thresholds,
larger R waves and, by targeting the distal conduction system, a lower
theoretical risk for developing distal conduction
block63. The LVSP could be an attractive way to
overcome the majority of the limitations of HBP. These include
difficulty in identifying the adequate location of the His bundle, high
and unstable threshold in up to 10% of patients, damage to the His
bundle during implantation, heart block distal to the His bundle,
undersensing R wave amplitude and oversensing atrial signals and lower
success rate in patients with left bundle branch block (LBBB) and heart
failure due to high pacing output required to correct
LBBB58,60,64–68. The rationale behind correcting
LBBB by HBP is that increased pacing output captures the left bundle
branch (LBB) beyond the area of block. El-Sherif et
al.69 showed that HBP required 20 V to capture the
LBB. Huang et al.62 first reported direct left bundle
branch pacing in patients with LBBB and heart failure. HBP at 10 V
failed to correct LBBB but after advancing the pacing tip towards the
left ventricle LBBB resolved at a low pacing capture threshold (0.5V).
The heart failure symptoms improved, LV ejection fraction improved and
adjustment of pacing parameters led to normalization of QRS. Chen et
al.70 used a transventricular septal approach for left
bundle pacing in patients with bradycardia. In their study, ECG
configuration changing from LBBB pattern to RBBB pattern was observed as
the pacing tip was advanced from the right interventricular septum to
capture the left bundle branch. Demonstration of left bundle potential
during intrinsic rhythm provided strong evidence of successful left
bundle pacing. Notably, paced ECG QRS duration was significantly shorter
(111.85±10.77 ms) compared with either RV septal pacing (154.80±9.85 ms)
or RV apical pacing (165.50±17.80 ms) with comparable capture threshold.
Interestingly, both left and right bundle branch block could be
corrected by left bundle pacing at low capture threshold. Interestingly,
both left and right bundle branch block could be corrected by LVSP at a
low capture threshold. Additionally, the QRS in LVSP is typically
<130ms instead of complete RBBB. It is also significantly
shorter than during RV pacing70,71. This may be
explained by retrograde activation of the right bundle during pacing or
connection between the main right and left bundle
branches72,73 or cell to cell
conduction74. The LVSP procedural success is 80.5-93%
in small studies71,75,76. Vijayaraman et
al76. reported periprocedural lead dislodgement in 3
of 97 patients who underwent LVSP. Potential complications for left
bundle pacing procedure include right bundle branch (RBB) injury during
the procedure, lead dislodgement, septal perforation and coronary artery
injury especially the septal perforators77.