What is the diagnosis and treatment for bifascicular block (a type of heart block characterized by impairment of two of the three main fascicles in the electrical conduction system of the heart)?

From the Guidelines

Bifascicular block patients with syncope, bundle branch block, and HV >70ms should receive permanent pacing (Class I) due to the high risk of developing complete atrioventricular block, as recommended by the 2018 ACC/AHA/HRS guideline 1.

Diagnosis and Presentation

Bifascicular block is a cardiac conduction abnormality involving two of the three fascicles of the His-Purkinje system, typically presenting as right bundle branch block (RBBB) combined with either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB). This condition is diagnosed through electrocardiogram (ECG) findings showing characteristic patterns: RBBB (wide QRS complex >120ms with RSR' pattern in V1 and wide S waves in leads I and V6) plus either LAFB (left axis deviation) or LPFB (right axis deviation).

Management

Most patients with bifascicular block are asymptomatic and require no specific treatment. However, monitoring is crucial as approximately 1-2% of patients per year may progress to complete heart block.

• Pacemaker implantation is generally not recommended for asymptomatic bifascicular block alone but should be considered in patients with:
  • Syncope or presyncope when other causes have been excluded
  • Evidence of intermittent complete heart block
  • Significantly prolonged HV interval on electrophysiology study
• The underlying cause of bifascicular block should be identified and treated, as it commonly results from coronary artery disease, cardiomyopathy, or degenerative fibrosis of the conduction system.
• Regular cardiac follow-up with periodic ECGs is recommended to monitor for progression to higher-degree heart block, as suggested by the European Society of Cardiology guidelines 1.

Prognosis and Treatment

The 2018 ACC/AHA/HRS guideline recommends permanent pacing for patients with bifascicular block and syncope, bundle branch block, and HV >70ms, due to the high risk of developing complete atrioventricular block 1. Additionally, cardiac resynchronization therapy (CRT) may be considered for patients with left ventricular ejection fraction (LVEF) 36-50%, left bundle branch block (LBBB), QRS >150 ms, and Class II or greater heart failure symptoms, as shown in the PROSPECT and REVERSE trials 1.

From the Research

Definition and Risks of Bifascicular Block

• Bifascicular block refers to a condition where there is a blockage in two of the three main electrical conduction pathways of the heart: the right bundle branch, the left anterior hemiblock, and the left posterior hemiblock 2.
• Patients with bifascicular block are at an increased risk of progression to complete heart block, which can lead to serious complications such as syncope, heart failure, and even death 3, 4, 5.

Predictors of Progression to Advanced Atrioventricular Block

• Studies have identified several predictors of progression to advanced atrioventricular block in patients with bifascicular block, including:
  • Syncope or presyncope 4, 5
  • QRS width >140 ms 4
  • Renal failure 4
  • HV interval >64 ms 4
• The presence of these risk factors can help identify patients who may benefit from prophylactic pacemaker implantation 4.

Management and Treatment

• The management of bifascicular block depends on the presence of symptoms and the risk of progression to complete heart block 3, 6.
• Patients with asymptomatic bifascicular block may not require immediate treatment, but should be closely monitored for signs of progression to complete heart block 2.
• Patients with symptomatic bifascicular block or those at high risk of progression to complete heart block may require pacemaker implantation or other treatments to prevent serious complications 3, 4, 6.