From the Guidelines
Left bundle branch block (LBBB) is most commonly caused by coronary artery disease, hypertension, and cardiomyopathy, as these conditions lead to damage or fibrosis of the cardiac conduction system, specifically affecting the left bundle branch. The causes of LBBB can be multifactorial, involving various cardiac and systemic diseases. According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1, assessment of cardiac structure and function is often clinically indicated in patients with conduction disorders, including LBBB.
Common Causes of LBBB
- Coronary artery disease
- Hypertension
- Cardiomyopathy
- Valvular heart disease (particularly aortic stenosis)
- Cardiac surgery complications
- Congenital heart defects
Less Common Causes of LBBB
- Infiltrative diseases such as sarcoidosis and amyloidosis
- Infectious processes like Lyme disease and Chagas disease
- Inflammatory conditions such as myocarditis
- Certain medications, including antiarrhythmics like flecainide and propafenone, as well as some calcium channel blockers
The pathophysiology of LBBB involves disruption of the normal electrical activation sequence, causing the left ventricle to depolarize later than the right ventricle, which can lead to mechanical dyssynchrony and potentially contribute to heart failure over time 1. Identifying the underlying cause of LBBB is crucial for appropriate management and prognosis assessment. A study published in the Journal of the American College of Cardiology found that LBBB was associated with significantly worse mortality and a decrease in left ventricular ejection fraction (LVEF) to ≤35% 1.
Importance of Underlying Cause Identification
- Crucial for appropriate management
- Crucial for prognosis assessment
- Helps guide treatment decisions, such as the potential need for cardiac resynchronization therapy (CRT) or permanent pacing.
From the Research
Causes of Left Bundle Branch Block (LBBB)
The causes of Left Bundle Branch Block (LBBB) can be attributed to various factors, including:
- Conduction system degeneration 2
- Myocardial pathology 2
- Aortic valve disease 2
- Cardiac procedures 2
- Primary conduction disease 3, 4
- Underlying pathology or iatrogenic factors 3, 4
Pathophysiology of LBBB
LBBB can lead to immediate electrical and mechanical dyssynchrony of the left ventricle (LV) and gradual structural damages in the Purkinje cells and myocardium 5. This can result in a reduction in left ventricular ejection fraction (EF) and potentially lead to heart failure (HF) 5.
Clinical Significance of LBBB
LBBB can affect patient diagnosis, treatment, and prognosis 3, 4. Accurate diagnosis of LBBB is crucial in guiding cardiac resynchronisation therapy 6. The European Society of Cardiology (ESC) has recently updated the diagnostic criteria for LBBB, highlighting the complexity of defining LBBB within the context of recent insights into the electromechanical pathophysiology of LBBB 6.