Electrical system of heart including SA node and AV node systems.

1. Cardiac electrical system
Prepared by: Anish Dhakal (Aryan)
anishdhakal718@gmail.com
MBBS Student
Patan Academy of Health Sciences

2. Objectives
• Describe SA node
• Describe the transmission of cardiac
impulse through Atria
• Describe AV node
• Describe bundle of His, Left Bundle
branch (LBB), Right Bundle branch
(RBB) and Purkinje fibers

3. Characteristics of Cardiac
Conduction Cells
• Automaticity: ability to initiate an
electrical impulse
• Excitability: ability to respond to an
electrical impulse
• Conductivity: ability to transmit an
electrical impulse from one cell to
another

4. Sinoatrial (SA) Node
:Pacemaker
• A primary pacemaker of the heart,
• The electrical impulses initiated by the
SA node are conducted along the
myocardial cells of the atria via
internodal pathways
• The impulses cause electrical
stimulation and subsequent contraction
of the atria

6. Self Excitation of Sinus Nodal Fibers

7. Conduction system
• The S-A node generate and coordinate
the transmission of electrical impulses
to myocardial cells
• The result is sequential atrioventricular
contraction which provides for the
most effective flow of blood , thereby
optimizing cardiac out put

8. Continued…..
• Cardiac conduction system: The
electrical conduction system controls
the heart rate
• This system creates the electrical
impulses and sends them throughout
the heart. These impulses make the
heart contract and pump blood.

9. Transmission of the cardiac
impulse through Atria
• Sinus nodal fibres directly connect with
surrounding atrial muscle fibre
• Several small bands of more conductive
atrial fibers are present in atria
Anterior Interatrial band (Bachmann’s Bundle)
3 Internodal pathways
 Anterior Internodal pathway
 Middle Internodal pathway
 Posterior Internodal pathways

10. Contd….
• Action potential travels outward into
the atrial muscle
• Action potential spread through the
entire atrial muscle mass, eventually to
AV node where A-V nodal delay occurs

12. Atrioventricular node
• The AV node consist of specialized muscle
cells similar to those of SA node
• The AV node coordinate the incoming
electrical impulses from atria
Cause of slow conduction in AV node:
• Diminished number of gap junctions
• Absence of this delay causes abnormal
pathway leads to Wolff-Parkinson-White
syndrome

13. Bundle of His (A-V Bundle)
• From the AV node, impulses travel
through to the right and left bundle
branches
• These branches extend to the right
and left sides of the septum and
bottom of the

14. Bundle of His
•These branch a lot to form the
Purkinje fibers that transmit the
impulses to the myocardium (muscle
tissue)
•The bundle of His, bundle branches
and Purkinje fibers transmit quickly
and cause both ventricles to contract
at the same time

15. Contraction of Ventricles
• As the ventricles contract, blood is
forced out through the semilunar valves
into the pulmonary trunk and the aorta.
• After the ventricles complete their
contraction phase, they relax and the
SA node initiates another impulse to
start another cardiac cycle.