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Bundle Branch Blocks
Dr.W A P S R Weerarathna
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
Right Bundle Branch Block (RBBB)
• QRS duration ≥ 120ms
• rSR’ pattern or notched R wave in V1
• Wide S wave in I and V6
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
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
Right Bundle Branch Block
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
Causes
• CAD Acute AWMI (new onset LBBB)
• Dilated Cardiomyopathy
• Aortic stenosis
• Long-standing hypertension
• Rate dependent LBBB
• RV paced rhythm
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
Left Bundle Branch Block
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
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
LAHB
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
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
LPHB
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