What is the most common form of bifascicular block?

What is the most common form of bifascicular block?

• A. Left bundle branch block (LBBB) and right anterior hemiblock
• B. Right bundle branch block (RBBB) and left anterior hemiblock
• C. Left bundle branch block (LBBB) and right posterior hemiblock
• D. Right bundle branch block (RBBB) and right anterior hemiblock

Answer: (B)

The most common form of bifascicular block is characterized by the combination of right bundle branch block (RBBB) and left anterior hemiblock. This combination occurs due to the functional impairment of two of the three main fascicles within the ventricular conduction system: the right bundle branch and the anterior division of the left bundle branch. RBBB is present when there is a delay or blockage in the conduction through the right bundle branch, which typically leads to a specific pattern on an electrocardiogram (ECG) including a QRS duration greater than 0.12 seconds and an rsR' pattern in leads V1 and V2. The addition of left anterior hemiblock implies that the anterior fascicle of the left bundle branch is also blocked, which often manifests as changes in the axis of the heart in the ECG, commonly resulting in a leftward shift. This combination is prevalent in patients with underlying structural heart disease such as left ventricular hypertrophy or ischemic heart conditions, making it more frequently observed than other types of bifascicular blocks. The other choices presented do reflect combinations of bifascicular blocks, but they are less commonly encountered in clinical practice compared to RBBB with left anterior hemiblock.

The most common form of bifascicular block is characterized by the combination of right bundle branch block (RBBB) and left anterior hemiblock. This combination occurs due to the functional impairment of two of the three main fascicles within the ventricular conduction system: the right bundle branch and the anterior division of the left bundle branch.

RBBB is present when there is a delay or blockage in the conduction through the right bundle branch, which typically leads to a specific pattern on an electrocardiogram (ECG) including a QRS duration greater than 0.12 seconds and an rsR' pattern in leads V1 and V2. The addition of left anterior hemiblock implies that the anterior fascicle of the left bundle branch is also blocked, which often manifests as changes in the axis of the heart in the ECG, commonly resulting in a leftward shift.

This combination is prevalent in patients with underlying structural heart disease such as left ventricular hypertrophy or ischemic heart conditions, making it more frequently observed than other types of bifascicular blocks. The other choices presented do reflect combinations of bifascicular blocks, but they are less commonly encountered in clinical practice compared to RBBB with left anterior hemiblock.