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