Trifascicular block

Question 1

Trifascicular block
RBBB
Axis deviation
First degree AV block

Answer 1

Trifascicular Block
1. Right Bundle Branch Block (RBBB)
* Broad QRS
* Inverted T waves in anterior leads
* Sloping ST in lateral leads
2. Axis Deviation
* Left Axis Deviation (LAD) = suggestive of Left Anterior Fascicular Block
* (Small R & deep S in II, III; large R in aVL)
* Right Axis Deviation (RAD) = suggestive of Left Posterior Fascicular Block
3. 1st Degree A-V Block (3rd fascicle)

⭐️ Classically progresses to Complete Heart Block (CHB)

Question 2

First degree HB

Answer 2

PR >200msec(>5small sq)

Causes:

Causes of First Degree Heart Block

Increased vagal tone
Athletic training
Inferior MI
Mitral valve surgery
Myocarditis (e.g. Lyme disease)
Electrolyte disturbances (e.g. Hyperkalaemia)
AV nodal blocking drugs (beta-blockers, calcium channel blockers, digoxin, amiodarone)
May be a normal variant

Question 3

second degree block
-Mobitz type 1
-Mobitz type 2

Answer 3

Mobitz type I-Wenckebach :
Mobitz Type I (Wenckebach AV block)

• Progressive prolongation of the PR interval culminating in a non-conducted P wave
• PR interval is longest immediately before the dropped beat
• PR interval is shortest immediately after the dropped beat

Mobitz type II
Mobitz Type II (Hay AV block)

• Intermittent non-conducted P waves without progressive prolongation of the PR interval
• PR interval in the conducted beats remains constant.
• RR interval surrounding the dropped beat(s) is an exact multiple of the preceding RR interval (e.g. double the preceding RR interval for a single dropped beat, treble for two dropped beats, etc).

Question 4

CHB

Answer 4

• Severe bradycardia due to absence of AV conduction
• The ECG demonstrates complete AV dissociation, with independent atrial and ventricular rates

=>causes :
same as for Mobitz I and Mobitz II second degree heart block.

• Inferior myocardial infarction
• AV-nodal blocking drugs (e.g. calcium-channel blockers, beta-blockers, digoxin)
• Idiopathic degeneration of the conducting system

=>Clinical significance

Patients at high risk of ventricular standstill and sudden cardiac death
Require
- cardiac monitoring,
-backup temporary pacing and usually
- insertion of a permanent pacemaker