What should be done if a patient has Right Bundle Branch Block (RBBB) and Left Anterior Fascicular Block (LAFB) of unknown duration?

From the Guidelines

If a patient has Right Bundle Branch Block (RBBB) and Left Anterior Fascicular Block (LAFB) of unknown duration, they should undergo observation and regular monitoring with follow-up ECGs to detect any progression of conduction disease, as prophylactic pacing in asymptomatic patients with conduction disorders has not been shown to be beneficial 1.

Key Considerations

• The combination of RBBB and LAFB, known as bifascicular block, may indicate underlying cardiac disease and carries an increased risk of progression to complete heart block.
• A comprehensive cardiac evaluation, including a detailed history and physical examination, 12-lead ECG, echocardiogram, and possibly additional testing such as stress testing or cardiac MRI, is essential to assess the patient's cardiac status.
• Patients should be referred to a cardiologist for evaluation and management of any underlying cardiac conditions.
• No specific medications are typically prescribed solely for the conduction abnormalities themselves, but any underlying cardiac conditions should be treated appropriately.
• If the patient experiences symptoms such as syncope, presyncope, or significant bradycardia, they may require permanent pacemaker implantation, as indicated by the management of conduction disorders algorithm 1.

Management Approach

• Regular monitoring with follow-up ECGs is crucial to detect any progression of conduction disease.
• The patient's cardiac status should be reassessed periodically to determine the need for any changes in management.
• The concern with bifascicular block is that it affects two of the three major fascicles of the cardiac conduction system, leaving only one functioning pathway for electrical impulses, which increases vulnerability to complete heart block if the remaining fascicle becomes compromised.
• As several studies from the 1970s demonstrated no benefit from prophylactic pacing in asymptomatic patients with conduction disorders, including combined RBBB and left anterior fascicular block, or bundle branch block, even in the presence of infranodal disease 1, a conservative approach with regular monitoring is recommended.

From the Research

Patient with RBBB and LAFB of Unknown Duration

If a patient has Right Bundle Branch Block (RBBB) and Left Anterior Fascicular Block (LAFB) of unknown duration, the following points should be considered:

• The combination of RBBB and LAFB may be related to the simultaneous occurrence of block of conduction through these components of the Purkinje network 2.
• Patients with RBBB and LAFB are at a higher risk of developing complete heart block (CHB) and sudden cardiac death (SCD) compared to those with only RBBB 3.
• The presence of RBBB may lead to the misdiagnosis of transmural ischemia and mask the early diagnosis of ST-elevation myocardial infarction 4.
• New-onset RBBB in acute myocardial infarction (AMI) patients is associated with a higher risk of long-term mortality, ventricular arrhythmia, and cardiogenic shock 4.

Management Considerations

Some key considerations for managing a patient with RBBB and LAFB include:

• Monitoring for signs of heart failure, arrhythmia, and first-degree atrioventricular block 3.
• Considering prophylactic pacemaker implantation in patients with trifascicular block (RBBB and LAFB or LPFB and septal LBBB) due to the high risk of CHB and SCD 3.
• Evaluating the patient's suitability for cardiac resynchronization therapy (CRT) or left bundle branch area pacing (LBBAP) if they have heart failure and reduced left ventricular systolic function 5.
• Assessing the patient's risk of developing complete heart block and sudden cardiac death, and considering appropriate preventive measures 3, 4.