Lightning Learning: Trifascicular Block
“Trifascicular block is a combination of heart block with a bifascicular block and can be ‘complete’ or ‘incomplete’.”
What?
Trifascicular block is a combination of heart block with a bifascicular block and can be complete or incomplete.
Bifascicular block is diagnosed by the presence of right bundle branch block with either left anterior fascicular block (common) or left posterior fascicular block (rare).
LAFB results in left axis deviation and LPFB in right axis deviation.
Complete trifascicular block: 3rd degree heart block in the presence of bifascicular block.
Incomplete trifascicular block: 1st or 2nd degree heart block with bifascicular block.
It can also be RBBB with alternating LAFB and LPFB.
Why?
Incomplete trifascicular blocks can convert into complete heart block. Any patient who presents with a trifascicular block on their ECG will need a medical or cardiology review. Many of these patients will require pacing, but be sure to review all medications.
Trifascicular block can result from:
Ischaemic heart disease
Congenital heart disease
Hyperkalaemia
Digoxin toxicity
Further Reading
- CanadiEM: The Boring Guide to ECG’s (Fascicular blocks)
- Life in the Fast Lane: Trifascicular Block
