Retrograde Conduction in Left Bundle Branch Block: Insights From Left Bundle Branch Pacing
Shunmuga Sundaram Ponnusamy1, William Basil2, Vithiya Ganesan3
1Department of Cardiology, Velammal Medical College, Madurai, India.
Insights
Left bundle branch pacing (LBBP) for heart failure (HF) with left bundle branch block (LBBB) showed that bidirectional block is linked to worse outcomes, while unidirectional block predicts better results and improved ejection fraction.
Area of Science:
- Cardiology
- Electrophysiology
- Heart Failure Management
Background:
- Biventricular pacing is standard for heart failure (HF), left bundle branch block (LBBB), and left ventricular (LV) dysfunction.
- Left bundle branch pacing (LBBP) offers an alternative to traditional biventricular pacing.
Purpose of the Study:
- To evaluate retrograde conduction properties of the left bundle branch during LBBP.
- To determine the clinical implications of these conduction properties in patients with nonischemic cardiomyopathy and LBBB.
Main Methods:
- Included patients with nonischemic cardiomyopathy, LBBB, and LV ejection fraction (LVEF) ≤35% undergoing LBBP.
- Assessed retrograde conduction using His potential recording, defining unidirectional and bidirectional block.
- Monitored HF hospitalization, ventricular arrhythmias, and mortality.
Main Results:
- Bidirectional block occurred in 82% of patients, associated with advanced HF and wider QRS.
- Unidirectional block occurred in 18%, linked to narrower paced QRS and higher LVEF.
- Unidirectional block predicted significantly better LVEF normalization (OR 4.1) and fewer adverse events (0% vs 12.5%).
Conclusions:
- Bidirectional block in LBBB correlates with more severe HF symptoms.
- Unidirectional block during LBBP is associated with superior clinical outcomes and improved cardiac function.
Background:
Biventricular pacing is a well-established therapy for patients with heart failure (HF), left bundle branch block (LBBB) and left ventricular (LV) dysfunction. Left bundle branch pacing (LBBP) has emerged as an alternative to biventricular pacing.
Objectives:
The aim of this study was to assess the retrograde conduction properties of the left bundle branch in patients with nonischemic cardiomyopathy and LBBB during LBBP and its clinical implications.
Methods:
Patients undergoing successful LBBP for nonischemic cardiomyopathy with LV ejection fraction (LVEF) ≤35% and LBBB were included. Continuous recording of His potential was performed using a quadripolar catheter. Unidirectional block was defined as retrograde His bundle activation during LBBP with stimulus to His potential (SH) duration less than or equal to antegrade HV interval and bidirectional block as VH dissociation or SH duration greater than HV interval. HF hospitalization, ventricular arrhythmias, and mortality were documented.
Results:
A total of 165 patients were included. The mean follow-up duration was 21.8 ± 13.1 months. Bidirectional block (group I) was observed in 82% (n = 136), and these patients were noted to have advanced HF stage and prolonged baseline QRS duration. Unidirectional block (group II) with intact retrograde conduction was observed in 18% (n = 29) and was associated with narrow paced QRS duration and higher LVEF during follow-up. Super-response (LVEF ≥50%) was observed in 54.4% (n = 74) in group I compared with 73.3% (n = 22) in group II (P = 0.03). The OR for LVEF normalization was 4.1 (95% CI: 1.26-13.97; P = 0.02), with unidirectional block compared with bidirectional block in patients with LBBB and LV dysfunction. Adverse clinical outcomes as measured by a composite of HF hospitalization, ventricular arrhythmias, and mortality were significantly higher in group I compared with group II (12.5% vs 0%; P = 0.04).
Conclusions:
Bidirectional block in LBBB was characterized by advanced HF symptoms, while unidirectional block was associated with better clinical outcomes after cardiac resynchronization therapy by LBBP.
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