Conducting System Of Heart

CONDUCTING SYSTEM OF HEART

• The conducting system is made ofspecialised myocardium (cardiac muscle), that is capable for initiation & conduction of cardiac impulse.
• It has following parts :

1. SA Node:

• SA Node is located in the upper part of crista terminalis at the junction of SVC and the right atrium.
• It is the pacemaker of the heart & generates impulse at a rate of 70-100/ min.
• SA Node is supplied by nodal artery, a branch of RCA in 65% cases & a branch of circumflex branch of LCA in 35% cases.
• SA Node is supplied by right vagus/parasympathetic (inhibitory) & right Sympathetic (excitatory) system as it develops from structures on the right side of embryo.
• SA Node consists of connective tissue stroma containing an irregular whorled network of cardiac nodal cells, the SA nodal artery & numerous nerve endings (postganglionic parasympathetic & postganglionic sympathetic).
• SA node is composed of a cluster of small fusiform cells.

2. AV Node:

• It lies in the right atrial floor near the interatrial septum in the‘triangle of koch’.
• It is supplied by AV nodal artery, a branch of RCA.
• AV node develops from left side of heart, thus is supplied by left vagus & left sympathetic fibers.
• Slowest in conduction.

3. Atrioventricular bundle or bundle of His :

• It arises from AV node & crosses the AV ring (annulus fibrosus).
• In the muscular septu,m it divides into right & left branches.
• It has a dual blood supply from AV nodal artery (branch of RCA) and anterior descending (interventricular) branch of LCA.

4. Right bundle branch (RBB) and left bundle branch (LBB):

• These bundle branches consist of modified muscle fibres (Purkinje fibers).
• Both RBB & LBB are supplied by LCA, except a small part of the LBB which is supplied by RCA.

• Purkinje fibers are specialised conducting fibers.
• Whole conduction system (including Purkinje fibers) is made up of modified cardiac muscles.
• Purkinje fibers allow the heart’s conduction system to create synchronized contractions of its ventricles, and are, therefore, essential for maintaining a consistent heart rhythm.
• Purkinje fibers are networks of fibers that receive conductive signals originating at the atrioventricular node (AVN), and simultaneously activate the left and right ventricles by directly stimulating the ventricular myocardium. 
• Purkinje fibers feature both wide diameters and many gap junctions, which both facilitate rapid impulse conduction.
• Maximum velocity of conduction.