Definition of Heart Block

It is defined as defect in either initiation or conduction of cardiac impulse.

Sites of Heart Block

• SA node.
• AV node.
• Bundle of His.
• Branches of bundle of His (left and right).

Types of Heart Block

1. SA block.
2. Atrioventricular block—It is of 3 types:
–– 1st degree AV block.
–– 2nd degree AV block. It is of 2 types:
— Mobitz type 1 (Wenckebach’s phenomenon).
— Mobitz type 2.
–– Complete heart block or 3rd degree heart block.
3. Bundle branch block:
–– Right bundle branch block (RBBB).
–– Left bundle branch block (LBBB).


It means when there is block involving one of the fascicles of left bundle branch. It is diagnosed
by seeing the axis deviation in ECG.
• When there is left-axis deviation—it is called left anterior hemiblock.
• When there is right-axis deviation—it is called left posterior hemiblock.
NB: There may be more blocks either two or three. In that case, it is called bifascicular or trifascicular block.