Conducting System of Heart

  • Maximum velocity of conduction is seen in Purkinje Fibres.
  • Cardiac tissue conduction velocity(fastest→slowest):Purkinje system → Atrial muscle→ Ventricular muscle → AV node.
  • Conduction rate is 4 m/s in purkinje fibers whereas it is 1 m/s in ventricular muscles, atrial pathways and Bundle of His. SA Node and AV Node has a conduction speed of 0.05 m/s
  • The slowest conduction velocity is in the AV node 
  1. Allows time to the atria to contract
  2. Allows complete ventricular filling
  3. The fastest Conduction velocity is in the Purkinje fibers 
  4. Allows the ventricles to contract at the same time simultaneously
  • Branches of the right coronary artery supplies the SA node, AV node and AV bundle. Right bundle branch of atrioventricular bundle is supplied by the left coronary artery. Left bundle branch is supplied by right and left coronary artery.
  • Function of M2 receptor in heart is SA Node Hyperpolarisation.
  • Conducting system of heart:
1.  SA node
  • It 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 and generates impulse at a rate of 70-100/min.SA node acts as a pacemaker of the heart because of the fact that it generates impulses at the highest rate.
  • SA node is suplied by nodal artery, a branch of RCA in 65% cases and a branch of circumflex branch of LCA in 35% cases.
  • One-third to one-half of patients with SA node dysfunction develop supraventricular tachycardia, usually atrial fibrillation or atrial flutter.
  • SA node is supplied by right vagus/parasympathetic (inhibitory) and right Sympathetic (excitatory) system as it develops from structures on the right side of embryo.
  • The SA node consists of connective tissue stroma containing an irregular whorled network of cardiac nodal cells, the SA nodal artery and numerous nerve endings (postganglionic parasympathetic and postganglionic sympathetic).
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 and left sympathetic fibers.

3.  Atrioventricular bundle or bundle of His :- It arises from AV node and crosses the AV ring (annulus fibrosus).
  • In the muscular septum it divides into right and 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 modifeid muscle fibers (Purkinje fibers). Both RBB and LBB are supplied by LCA, except a small part of the LBB which is supplied by RCA.
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