• Ventricular Conduction System
• Trifascicular Block
• Variants of Trifascicular Block
• Alternating Bundle Branch Block
• Alternating Bifascicular Block
• RBBB + AV Block II Degree (Mobitz II)
• LBBB + AV Block II Degree - Mobitz II
• Bifascicular Block + AV Block First Degree
• LBBB + First Degree AV Block
• Bifascicular Block + Second Degree AV Block (Mobitz I)
• LBBB + Second Degree AV Block (Mobitz I)
• Complete Trifascicular Block

Ventricular Conduction System

• The conduction system in the ventricles has 3 pathways:
• Right Bundle Branch (RBB)
• The Left Bundle Branch divides into:
• Left Anterior Fascicle (LAF)
• Left Posterior Fascicle (LPF)
  
  
• When one pathway is interrupted, blocks occur:
• Right Bundle Branch Block (RBBB)
• Left Bundle Branch Block (LBBB)
• Left Anterior Fascicular Block (LAFB)
• Left Posterior Fascicular Block (LPFB)
  
  
• In the case of AV junction malfunction, AV blocks occur:
• AV Block I
• AV Block II - Mobitz I (Wenckebach)
• AV Block II - Mobitz II
• AV Block III (Complete AV Block)

Variants of Trifascicular Block

• Trifascicular Block
  • Is a combination of AV blocks and Bundle Branch Blocks, where all 3 pathways are affected
• The most common variant of trifascicular block is:
• Bifascicular Block + AV Block I
  
  
• Variants of Trifascicular Block:
• Alternating Bundle Branch Block (RBBB/LBBB)
• Alternating Bifascicular Block (RBBB + LAF/LPF)
• RBBB + AV Block II - Mobitz II
• LBBB + AV Block II - Mobitz II
• Bifascicular Block + AV Block I
• LBBB + AV Block I
• Bifascicular Block + AV Block II - Mobitz I
• LBBB + AV Block II - Mobitz I
• Complete Trifascicular Block

Alternating Bifascicular Block

• Bifascicular block has 2 variants
• RBBB + LAFB
• RBBB + LPFB
• On the ECG, both variants alternate

LBBB + AV Block II Degree - Mobitz II

• It is LBBB and AV Block II Degree (Mobitz II)
• AV Block II Degree - Mobitz II
• is an intermittent conduction disturbance
• almost always (75%) infra-Hisian (at the level of the bundle branches)
• On the ECG, you will see LBBB and AV Block II Degree (Mobitz II)

LBBB + First Degree AV Block

• It is LBBB and First Degree AV Block
• On the ECG, you will see LBBB and First Degree AV Block

LBBB + Second Degree AV Block (Mobitz I)

• It is LBBB and Second Degree AV Block (Mobitz I)
• The AV node shows Wenckebach Phenomenon
• The PQ interval progressively lengthens until the P wave is blocked
• On the ECG, you will see LBBB and Second Degree AV Block - Mobitz I

Trifascicular Block (Bifascicular Block + First Degree AV Block)

• Most common variant of Trifascicular Block
• is Bifascicular Block + First Degree AV Block
• Bifascicular Block
• Right Bundle Branch Block (RBBB)
• Widened QRS ≥ 0.12s
• rsR (V1)
• Deep S (V6)
• Left Anterior Hemiblock (LAH)
• Positive QRS (I)
• Negative QRS (II, III)
• First Degree AV Block
• Prolonged PQ Interval > 0.2s

Trifascicular Block (Alternating Bundle Branch Block)

• At the beginning of the ECG is Left Bundle Branch Block (LBBB)
• After a premature atrial contraction
• There is a change to Right Bundle Branch Block (RBBB)
• It indicates severe damage to the conduction system
• Both bundle branches are damaged
• PQ interval during LBBB is longer than the PQ interval during RBBB
• This indicates that the right bundle branch is more damaged
• Because it takes longer to activate the ventricles
• Such a patient may develop
• Second Degree AV Block - Mobitz II
• Third Degree AV Block
• A patient with this type of ECG is indicated for pacemaker implantation
• Alternating Bundle Branch Block is considered a Trifascicular Block