Relationship between myocardial fibrosis and left bundle branch block. Does it exist?

Area of Science:

• Cardiology
• Cardiac Imaging
• Pathology

Background:

• Left bundle branch block (LBBB) is a common finding in patients with dilated cardiomyopathy (DCM).
• The underlying substrate and relationship between cardiac fibrosis and LBBB in DCM remain incompletely understood.
• Differentiating LBBB causes is crucial for prognosis and management.

Purpose of the Study:

• To investigate the association between focal and diffuse left ventricular (LV) fibrosis and LBBB in patients with DCM.
• To compare fibrosis patterns in DCM patients with and without LBBB, and in those with idiopathic LBBB.

Main Methods:

• Cardiovascular magnetic resonance (CMR) with late gadolinium enhancement (LGE) was used to assess focal fibrosis (core scar and gray zone) and diffuse fibrosis (diffuse intensity ratio - DIR).
• Endomyocardial biopsy (EMB) quantified collagen volume fraction (CVF) in a subset of patients.
• Study included DCM patients with LBBB (DCM-LBBB), DCM without LBBB (DCM-nonLBBB), idiopathic LBBB, and healthy volunteers (HV).

Main Results:

• No significant difference in focal or diffuse fibrosis was found between DCM-LBBB and DCM-nonLBBB patients.
• CVF correlated with DIR, supporting DIR as a measure of diffuse fibrosis.
• Patients with idiopathic LBBB showed higher DIR values compared to HV, suggesting underlying diffuse myocardial changes.

Conclusions:

• Focal and interstitial fibrosis are not associated with LBBB in DCM.
• Diffuse inflammation in DCM-LBBB may contribute to systolic dysfunction but does not cause LBBB.
• Increased interstitial fibrosis in idiopathic LBBB may indicate a latent process leading to DCM development.