1. Bundle Branch Blocks
Dr.W A P S R Weerarathna

3. Blood supply
• RCA (proximal)  Sinus nodal artery
• LAD  Septal branch to proximal RBB
and anterior LBB.
• LAD (septal) & RCA (terminal) 
Posterior fascicle of LBB
• PDA  AV nodal branch and bundle of
HIS supply

4. Right Bundle Branch Block (RBBB)
• QRS duration ≥ 120ms
• rSR’ pattern or notched R wave in V1
• Wide S wave in I and V6

5. Causes
• Normal variant in 0.2% of adults.
• CAD  Acute anterior MI (occlusion of proximal
LAD)
• Pulmonary hypertension (COPD)
• Acute pulmonary embolism
• Congenital heart disease e.g. ASD, Ebstein’s
anomaly
• Rate dependent RBBB
• Rare: Brugada syndrome

6. Clinical significance
• RBBB is commonly seen and is usually
benign
• RBBB in the setting of an acute MI
worsens the prognosis (indicates proximal
LAD occlusion)
• Presence of RBBB on ECG is not a
contraindication for TMT

7. Right Bundle Branch Block

9. Left Bundle Branch Block (LBBB)
• QRS duration ≥ 120ms
• Broad R wave in I and V6
• Prominent QS wave in V1
• Absence of q waves (including physiologic
q waves) in I and V6

10. Causes
• CAD  Acute AWMI (new onset LBBB)
• Dilated Cardiomyopathy
• Aortic stenosis
• Long-standing hypertension
• Rate dependent LBBB
• RV paced rhythm

11. Clinical significance
• New onset LBBB is an indication for thrombolytic
therapy
• LBBB in the setting of an acute MI worsens the
prognosis
• Standard LVH criteria are not valid in presence
of LBBB
• LBBB may mask signs of myocardial infarction
• LBBB on ECG is a contraindication for TMT
• Presence of LBBB in heart failure indicates
ventricular dyssynchrony

12. Left Bundle Branch Block

14. Diagnosis of MI in the presence of
LBBB
• Sgarbossa criteria: Points
• ST segment elevation of ≥1mm 5
concordant with QRS complex
• ST depression ≥ 1mm in leads V1-V3 3
• ST segment elevation ≥5mm and 2
discordant with QRS complex
• Score ≥ indicates Acute MI

15. Left anterior hemiblock (LAHB)
• Left axis deviation (> -30 degrees)
• Duration of QRS complex < 120msec
• qR morphology in Lead I, aVL
• rS morphology in Leads II, III, aVF
• ‘q1S3’ pattern
• Slurred S waves in left precordial leads

16. LAHB

17. LAHB - significance
• May be normal variant
• Occurs in HTN, Cardiomyopathy
• May be seen in acute MI (LAD territory)
• Masks old inferior wall MI by abolishing
the diagnostic Q-waves in II, III, and aVF
LAHB is more common than LPHB

18. Left Posterior hemiblock
• The duration of the QRS complex axis is
normal (<120msec)
• QRS axis is ≥ +120° (RAD)
• Prominent Q wave in leads II, III, and aVF
• rS complexes in Leads I, aVL
• ‘S1Q3’ pattern

19. LPHB

20. LPHB – significance
• LPHB may mimic old IWMI due to Q
waves in II, III, aVF
• LPHB in the setting of Anterior MI
indicates extensive damage to the
conduction system and poor prognosis
• Other causes of RVH are to be excluded
before diagnosing LPHB