Defining Left Bundle Branch Block Patterns in Cardiac Resynchronisation Therapy: A Return to His Bundle Recordings
Roderick Tung1, Gaurav A Upadhyay1
1Center for Arrhythmia Care, Pritzker School of Medicine, University of Chicago, Chicago, IL, US.
Insights
Left bundle branch block (LBBB) is often proximal, not diffuse. Left-sided His bundle pacing (HBP) effectively corrects QRS in these patients, improving cardiac resynchronisation therapy (CRT) selection.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Devices
Background:
- Left bundle branch block (LBBB) is linked to better outcomes with cardiac resynchronisation therapy (CRT).
- Traditionally, LBBB was thought to stem from widespread distal conduction system disease.
- His bundle pacing (HBP) can normalize wide QRS, challenging traditional LBBB pathophysiology assumptions.
Purpose of the Study:
- To investigate the location of conduction block in patients with LBBB.
- To determine if the location of block predicts response to His bundle pacing (HBP) for resynchronisation.
- To refine patient selection for cardiac resynchronisation therapy (CRT).
Main Methods:
- Utilised an extended invasive electrophysiology study (EPS) with left-sided recordings.
- Assessed conduction block in patients with LBBB pattern.
- Correlated QRS correction with HBP to the site of conduction block.
Main Results:
- Conduction block in LBBB is typically proximal, often in left-sided His fibres.
- Patients with proximal block showed the greatest QRS correction with HBP.
- Intact Purkinje activation or intraventricular conduction delay predicted less benefit from HBP.
Conclusions:
- LBBB pathophysiology often involves proximal conduction block.
- Left-sided EPS can identify patients likely to benefit from HBP for CRT.
- This approach may improve patient selection for CRT and phenotyping conduction disorders.
Abstract:
Left bundle branch block (LBBB) is associated with improved outcome after cardiac resynchronisation therapy (CRT). One historical presumption of LBBB has been that the underlying pathophysiology involved diffuse disease throughout the distal conduction system. The ability to normalize wide QRS patterns with His bundle pacing (HBP) has called this notion into question. The determination of LBBB pattern is conventionally made by assessment of surface 12-lead ECGs and can include patients with and without conduction block, as assessed by invasive electrophysiology study (EPS). During a novel extension of the classical EPS to involve left-sided recordings, we found that conduction block associated with the LBBB pattern is most often proximal, usually within the left-sided His fibres, and these patients are the most likely to demonstrate QRS correction with HBP for resynchronisation. Patients with intact Purkinje activation and intraventricular conduction delay are less likely to benefit from HBP. Future EPS are required to determine the impact of newer approaches to conduction system pacing, including intraseptal or left ventricular septal pacing. Left-sided EPS has the potential to refine patient selection in CRT trials and may be used to physiologically phenotype distinct conduction patterns beyond LBBB pattern.
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