What are bundle branch blocks (BBB)?

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Last updated: February 20, 2025 • View editorial policy

From the Guidelines

Bundle branch blocks are electrical conduction abnormalities in the heart that affect how electrical signals travel through the ventricles, occurring when one of the bundle branches is damaged or blocked, causing a delay in ventricular activation, as described in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. To understand bundle branch blocks, it's essential to recognize the two main types:

  • Right Bundle Branch Block (RBBB): characterized by a wide QRS complex (>120 ms) with an rSR' pattern in V1-V3, and T wave inversions in right precordial leads, typically asymptomatic and not requiring specific treatment.
  • Left Bundle Branch Block (LBBB): characterized by a wide QRS complex (>120 ms) with broad, notched R waves in I, aVL, V5-V6, and absence of Q waves in leads I, V5, and V6, which may cause reduced cardiac efficiency and requires evaluation for underlying heart disease. Management of bundle branch blocks involves:
  • Identifying and treating underlying causes, such as coronary artery disease or hypertension
  • Monitoring for progression to complete heart block, especially in bilateral bundle branch block
  • Considering cardiac resynchronization therapy in patients with LBBB and heart failure, as recommended by the 2018 ACC/AHA/HRS guideline 1. It's crucial to understand that no specific medications are routinely prescribed for bundle branch blocks alone, and the focus is on managing underlying conditions and preventing complications, ultimately improving morbidity, mortality, and quality of life.

From the Research

Definition and Types of Bundle Branch Blocks

  • Bundle branch blocks (BBB) are a type of cardiac conduction disorder that affects the electrical pathways of the heart 2, 3, 4, 5, 6.
  • There are two main types of bundle branch blocks: left bundle branch block (LBBB) and right bundle branch block (RBBB) 2, 4, 6.
  • A third, less common type is bilateral bundle branch block (BBBB), which exhibits features of both LBBB and RBBB 6.

Characteristics of Bundle Branch Blocks

  • LBBB is characterized by a delay or block in the left bundle branch, resulting in a prolonged QRS complex 4, 5.
  • RBBB is characterized by a delay or block in the right bundle branch, resulting in a terminal R wave in lead V1 2, 6.
  • BBBB is characterized by an RBBB pattern in lead V1 and an LBBB pattern in leads I and aVL, with an absence of S wave in leads I and aVL 2, 6.

Diagnosis and Prevalence of Bundle Branch Blocks

  • The diagnosis of bundle branch blocks can be made using electrocardiography (ECG) 2, 3, 4, 5, 6.
  • The prevalence of bundle branch blocks varies, with LBBB being more common than RBBB, and BBBB being relatively rare 2, 6.
  • The absence of S waves in leads I and aVL during RBBB is 100% specific and 64% sensitive for the presence of pre-existing LBBB 2.

References

Research

Electrocardiographic features and prevalence of bilateral bundle-branch delay.

Circulation. Arrhythmia and electrophysiology, 2014

Research

Left Bundle Branch Block: Current and Future Perspectives.

Circulation. Arrhythmia and electrophysiology, 2020

Research

Evaluating strict and conventional left bundle branch block criteria using electrocardiographic simulations.

Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology, 2013

Research

Bilateral Bundle Branch Block.

Cardiac electrophysiology clinics, 2021

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.