A summarized lecture on the conducting system of the heart.

1. CONDUCTING SYSTEM
OF THE HEART
- DR. MANISH
KHAREL

2. WHAT IS
CONDUCTING
SYSTEM OF THE
HEART?The cardiac conduction system is a group of
specialized cardiac muscle cells (myocytes) in
the walls of the heart (myocardium) that send
signals (cardiac impulse) to the heart muscle
resulting in the rhythmical contraction of
cardiac muscle. It is also called as the electric
system of the heart.
The main components of the cardiac
conduction system are the
• SA node,
• AV node,
• AV bundle or bundle of His,
• Right and Left bundle branches, and
• Purkinje fibers.

4. ELECTRICAL
SYSTEM OF THE
HEART
• Well lablled
diagrammatic
representation of
conduction
pathway of human
heart!

5. SINOATRIAL NODE (SA NODE)
The sinoatrial (SA) node is a collection of specialised cells
(pacemaker cells), and is located in the upper wall of the right atrium,
at the junction where the superior vena cava enters. It is called the “
pacemaker of the heart “ (MCQ)
These pacemaker cells can spontaneously generate electrical
impulses. The wave of excitation created by the SA node spreads
across both atria, resulting in atrial contraction (atrial systole) – with
blood moving from the atria into the ventricles.
The rate at which the SA node generates impulses is influenced by
the autonomic nervous system:
• Sympathetic nervous system – increases firing rate of the SA node,
and thus increases heart rate.
• Parasympathetic nervous system – decreases firing rate of the SA
node, and thus decreases heart rate.

6. ATRIOVENTRICULAR NODE
After the electrical impulses spread across the atria,
they converge at the atrioventricular node – located
near the wall of the atrial septum near the AV valves.
This wave of excitation (impulse) then passes from
the atrioventricular node into the atrioventricular
bundle.
AV node is also capable of generating cardiac
impulse but at a slower rate than SA node.
It generates the impulse at the rate of 40-60 beats
per minute. (MCQ)

7. ATRIOVENTRICULAR BUNDLE
The atrioventricular bundle (bundle of His) is a continuation of
the specialised tissue of the AV node, and it transmits the
electrical impulse from the AV node to the Purkinje fibers of the
ventricles.
At the upper end of the interventricular septum, it divides into
two main bundles:
Right bundle branch – conducts the impulse to the Purkinje
fibers of the right ventricle
Left bundle branch – conducts the impulse to the Purkinje
fibers of the left ventricle.

8. PURKINJE FIBERS
The purkinje fibers arise from the right and
left branches of bundle of His (AV bundle).
It produces impulse at the rate of 10-40 beats
per min.
It spreads impulse to all part of ventricles.
This rapid conduction allows coordinated
ventricular contraction (ventricular systole) and
blood is moved from the right and left
ventricles to the pulmonary artery and aorta

9. Key facts about the cardiac conduction system
Parts Nodal tissue: sinoatrial (SA) and atrioventricular (AV) nodes
Conducting fibers: internodal and interatrial conduction pathways, bundle of
His, bundle branches, subendocardial branches (purkinje fibres)
Sinuatrial node Contains cardiac pacemaker (P) cells
Pacemaker of the heart
Supplied by the SA nodal branch of the right coronary artery
Internodal conduction
pathway
Anterior, middle, posterior
Interatrial conduction
pathway
Conducts impulses to the left atrium
Supplied by the SAnodal artery
Atrioventricular node Secondary pacemaker
Supplied by AV nodal artery
Bundles Atrioventricular (AV) bundle (of His)
Right and left bundles
Subendocardial branches (Purkinje fibers)
Physiology (Pathway
of conduction)
Impulse starts at the SA node → internodal and interatrial conduction pathways → AV
node → AV bundle (of His) → bundle branches → subendocardial branches (Purkinje
Fibers)
Sympathetic: increases the rate of SA node activity
Parasympathetic: decreases the rate of SA node activity

10. LETS MAKE IT EASY!

11. HIGH YIELD POINTS (MCQ BASED)
Depolarization means the contraction whereas repolarization
means relaxation.
SA node represents atrial depolarization.
Atrial depolarization is represented by P wave in ECG.
AV node and bundle of His represents ventricular
depolarization.
Ventricular depolarization is represented by QRS complex in
ECG.
Purkinje Fibers represents ventricular repolarization.
Ventricular repolarization is represented by T wave in ECG.

12. PROPERTIES OF CARDIAC MUSCLE
Property # 1.Rhythmicity/Automaticity/Chronotropism:
• In the myocardium, automaticity is the ability of the cardiac muscles to
depolarize spontaneously, without external electrical stimulation from the
nervous system.
Property # 2. Excitability (Bathmotropism):
• Is the ability of cardiac muscle to respond to adequate stimuli by generating
an action potential.
Property # 3. Contractility/Inotropism:
• It is the ability of the cardiac muscle to convert electrical energy into
mechanical work.
Property # 4. Conductivity (Dromotropism):
• Is the ability of cardiac muscle fibers to conduct the cardiac impulses that
are initiated in the SA node (the pacemaker of the heart).

13. Have a great
day!