The combination of right bundle branch block, left anterior or posterior fascicular block and first degree AV block is often referred to as trifascicular block.

It is difficult to determine from ECG whether this pattern represents true bifascicular block and impending failure of the remaining fascicle, or whether coexistant bifascicular block and first degree AV block are two distinct pathologies.

The presence of alternating bundle branch block suggests that a patient is at high risk of developing complete heart block.

Fixed right bundle branch block with alternating left anterior and left posterior fascicular block suggests that a patient is at high risk of developing complete heart block.

When there is block of the right bundle branch and either the left bundle branch or both left anterior and posterior fascicles, complete AV block occurs.