Definition
- The cardiac conduction system (SA node, internodal pathways, AV node, His bundle, bundle branches, Purkinje fibers) generates and conducts the cardiac impulse.
- The SA node is the primary pacemaker; its spontaneous diastolic depolarization is the pacemaker potential (prepotential).
Conducting System of the Heart
Conduction velocity in the conducting system
Tissue
SA node
- Velocity (m/s)
- 0.05
AV node
- Velocity (m/s)
- 0.05
Internodal pathways
- Velocity (m/s)
- 1
His bundle
- Velocity (m/s)
- 1
Ventricular muscle
- Velocity (m/s)
- 1
Purkinje fibers
- Velocity (m/s)
- 4 (highest)
- SA node (right atrium) is the primary pacemaker; AV node connects atria to ventricles via His bundle, bundle branches and Purkinje fibers.
- SA node lies near the opening of the superior vena cava and contains pacemaker (P) cells.
- Three internodal pathways connect SA to AV node:
- Anterior (Bachmann)
- Middle (Wenckebach)
- Posterior (Thorel)
- Bachmann's bundle also carries impulse directly to the left atrium.
- AV node lies near the interatrial septum, above the AV ring; small fiber diameter and few gap junctions cause AV nodal delay.
- His bundle divides into right and left bundle branches, terminating as Purkinje fibers in the sub-endocardium of both ventricles.