LBBB

Question 1

✅ Causes

Answer 1

• Ischemia
  
  • Aortic Stenosis (AS)
  • Dilated Cardiomyopathy (CMP)
  • Degenerative disease of the conductive system
  • Drug toxicity

AICDD

Question 2

✅ ECG Features

Answer 2

1. Deep S in V1
   
   2. Absent Q waves in lateral leads
      * (RV depolarizes first → eliminates septal Q waves in lateral leads)
   3. Deep & broad R in lateral
   4. Prolonged R wave peak time in lateral leads
   5. Left Axis Deviation (LAD)
   6. QRS & ST segment +Twaves in opposite directions (i.e. discordant)

Question 3

Mx

Answer 3

• Incomplete LBBB = LBBB features but normal QRS duration
  • LBBB is an independent predictor of mortality in CAD
  • ↓ EF < 35% → consider PPM

Question 4

✅ ECG Features – LAFB

Answer 4

• Left Axis Deviation (LAD)
  
  • Normal or slightly prolonged QRS (<120 msec)
  • Small R + Deep S waves in inferior leads (II, III, aVF)
  • Small Q + tall R waves in lateral leads (I, aVL)
  • Fascicle block alters the direction but not the duration of QRS
  • R wave peak time = prolonged (>35 msec in I, aVL)

• Normal geometry: small R waves in I, aVL, large Q in III, aVF
  
  • LAFB: Reverses this pattern
    → Large R in I, aVL
    → Deep S in inferior leads

Question 5

🧠 Causes OF LAFB

Answer 5

🧠 Causes:
* Can be normal variant
* Severe LAD disease
* Post-infarction scar
* Aortic valve disease
* Degenerative conduction disease

Question 6

🧠 LPFB (Left Posterior Fascicular Block)
ECG features

Answer 6

• Right Axis Deviation (usually > +110°)
  
  • Normal or slightly prolonged QRS duration (<120 ms)
  • Small R waves with deep S waves in leads I and aVL
  • Small Q waves with tall R waves in leads II, III, and aVF

❗ To Diagnose LPFB:
* Must exclude other causes of RAD, especially:
* Right ventricular hypertrophy (RVH)
* Pulmonary disease
* Lateral myocardial infarction

Question 7

Causes of LPFB

Answer 7

⭐ LPF (Left Posterior Fascicle)
* LPF has dual blood supply → LAD + AV nodal artery
* ⭐ If IHD is the cause, it is severe

⸻

📌Other Causes:
* Myocarditis
* Cardiomyopathy (CMP)

Question 8

LAFB vs LPFB
comparision table

Answer 8

Question 9

Clues to diagnosing LAFB and LPFB

Answer 9

🔺 Trifascicular Block

= RBBB + LAFB/LPFB + 1° AV Block

⸻

⭐ Quick clinical tip:

When you see an RBBB, look at Axis and lead III
* RBBB + LAD + deep S in III → suggests RBBB + LAFB
* RBBB + RAD + tall R in III → suggests RBBB + LPFB