Bundle of His divides into right and left branches. The left branch divides into three divisions:

  1. Anterior,
  2. Posterior, and
  3. Septal.

All these branches may be involved singly or in combinations.

Causes of Right bundle branch block

N.B. It is a normal finding in all ages.

  1. Emphysema and fibrosis of lung.
  2. Right ventricular enlargement.
  3. Atrial septal defect, VSD
  4. Ebstein’s anomaly.
  5. Pulmonary embolism.
  6. Ischaemic heart disease.
  7. Carditis from any cause.
  8. Endomyocardial fibrosis and cardiomyopathy.
  9. Drugs, e.g. Quinidine and Procainamide, others.
  10. Congenital heart, disease including coarctation of aorta.
  11. Idiopathic fibrosis.
  12. Surgery and trauma.
  13. Brugada syndrome and Rv dysplasia.

Left bundle branch block:

  1. Ischaemic and hypertensive heart disease.
  2. Left ventricular enlargement.
  3. Carditis.
  4. Endomyocardial fibrosis and cardiomyopathy.
  5. idiopathic fibrosis.
  6. drugs like quinidine and procainamide, others.
  7. surgery and trauma.

Clinical Features:

Bundle branch block is essentially diagnosed from ECG but clinically in RBBB wide splitting of S, is seen with evidence of right ventricular enlargement. Similarly in LBBB reversed splitting of the second heart sound with evidence of left ventricular enlargement may be found.

Diagnosis of bundle branch block:

This is based on ECG finding.RBBB: Right axis, wide QRS duration (0.12 second or more in complete RBBB; in incomplete RBBB 0.10 to just below 0.12 second), wide S in lead I, intrinsicoid, deflection over V1 is more than 0.02 sec and there is rSR or M pattern. When left anterior fascicular block is present in addition, there will be left axis, deep S in Leads II, III, q in I and aVL and r in III, and R in aVL.

LBBB: Left axis, wide QRS (0.12 second or more in complete LBBB; 0.10 to just below 0.12 second in incomplete LBBB), wide, notched and slurred R in Leads I, aVL, V Intruisicoid dylection in V5-6 is more than 0.05 sec. BUNDLE BRANCH BLOCK

Left anterior fascicular block: Narrow QRS duration, small g in Leads I, aVL and small r in Lead III, mean frontal plane QRS axis is -30°. This is also called left anterior hemiblock .

Left posterior fascicular block: Narrow QRS duration mean frontal plane axis +900. Small q in III and small r in I and aVL. This is also called left posterior hemiblock.

Septal fascicular block: Absence of Q wave in V5-6. Bifasicular block: It is consists of RBBB with any of Left anterior and posterior fasicular block.

Trifasicular block: it consist of RBBB, with left anterior fasicular block and left posterior fasicular block.


This is done acceding to the underlying cause. When syncope is present pace-maker should be implanted.