What is a right posterior bundle branch block (BBB) fascicle?

Right Posterior Bundle Branch Block Fascicle

The right posterior fascicular block is part of the specialized cardiac conduction system, specifically a division of the right bundle branch that supplies the posterior portion of the right ventricle, and its blockage can contribute to complex conduction disorders with potential implications for cardiac function and risk assessment.

Anatomy of the Cardiac Conduction System

• The normal cardiac conduction system consists of the sinus node, atrial muscle, atrioventricular node, His bundle, bundle branches, fascicles, Purkinje fibers, and ventricular muscle 1
• The His bundle divides into left and right bundle branches, with the left bundle further dividing into anterior and posterior fascicles 1, 2
• The right bundle branch similarly divides into anterior, middle (lateral), and posterior fascicles, though this is less commonly discussed in clinical practice 3

Characteristics of Right Posterior Fascicular Block

• Right posterior fascicular block is characterized by delayed conduction through the posterior division of the right bundle branch 3
• Diagnostic ECG features include:
  • Delayed R-peak time in leads aVR and V1
  • Right axis deviation exceeding +60°
  • Specific ventricular complex morphologies 3
• This conduction abnormality is often overlooked during diagnostic processes and presents a challenge in ECG interpretation 3

Clinical Significance and Implications

• Right fascicular blocks are less commonly recognized than left fascicular blocks but may have similar clinical implications 3
• When right posterior fascicular block occurs in combination with other conduction abnormalities (such as left bundle branch block), it may contribute to bifascicular or trifascicular block patterns 4
• The presence of complex conduction abnormalities involving multiple fascicles reflects extensive involvement of the specialized conduction system and carries an increased risk of clinically significant AV block 1, 2

Evaluation and Management

• Demonstration of fascicular blocks should lead to a cardiological work-up including exercise testing, 24-hour ECG monitoring, and cardiac imaging to evaluate for underlying pathological causes 1
• In patients with conduction system disease where AV block is suspected, ambulatory electrocardiographic monitoring is useful 1
• ECG interpretation in patients with complex conduction abnormalities requires careful analysis and correlation with clinical findings 2

Etiologies and Associated Conditions

• Fascicular blocks may develop from various causes including:
  • Primary degenerative lesions of specialized conducting tissue
  • Ischemic or hypertensive heart disease
  • Cardiomyopathies
  • Myocarditis
  • Channelopathies
  • Cardiac tumors
  • Sarcoidosis
  • Chagas' disease
  • Congenital heart disease 1, 2
• Right fascicular blocks have been observed during right heart catheterization procedures using Swan-Ganz catheters, suggesting mechanical trauma as a potential cause 5

Prognostic Implications

• The combination of right bundle branch block with fascicular blocks of the left bundle branch (bifascicular block) has been associated with poor prognosis, as it may develop into trifascicular block or complete atrioventricular block 4
• In patients with acute myocardial infarction, the development of complex conduction disturbances including fascicular blocks may indicate more extensive myocardial injury 1

Special Considerations

• ECG screening of family members may be warranted when complex conduction abnormalities are identified in young individuals 1
• The diagnosis of right posterior fascicular block should prompt consideration of underlying structural heart disease, particularly in athletes where bundle branch blocks are uncommon (<2% of athlete's ECGs) 1, 2