Download Electrical Conductivity System of the Heart

Dr.Sisara Bandara Gunaherath
MBBS
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The heart is the pump responsible for
maintaining adequate circulation of
oxygenated blood around the vascular network
of the body.
It is a four-chamber pump, with the right side
receiving deoxygenated blood from the body at
low pressure and pumping it to the lungs (the
pulmonary circulation) and the left side
receiving oxygenated blood from the lungs and
pumping it at high pressure around the body
(the systemic circulation).
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The S-A Node is the most important element in
the electrical circuit of the heart.
It starts the cardiac cycle by periodically
generating action potentials without any
external stimulation. (Therefore, it is said to be
autorhythmic.)
It is also known as the pacemaker of the heart.
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In the right atrium
Near the opening of the superior vena cava
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Action potentials that originate in the SA node
spread to adjacent myocardial cells of the right
and left atria through the gap junctions
between these cells
Since myocardium of the atria is separated
from the myocardium of the ventricles by
fibrous skeleton of the heart , however the
impulse cannot be conducted directly from
atria to the ventricles
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Therefore specialized conducting tissue (
modified myocardial cells) need for electrical
conduction of the heart
These specialized myocardial cells form the AV
node, Bundle of His ( Atrioventricular bundle)
and Purkinje fibers
Once the impulse has spread through atria , it
passes to the AV node, which located on the
inferior portion of the interatrial septum; from
there impulse continues through the bundle of
His , beginning at the top of the
interventricular septum
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The bundle of His divides in to right and left
bundle branches , which are continuous with
the Purkinje fibers with in the ventricular walls
Stimulation of Purkinje fibers causes both
ventricles to contract simultaneously and eject
blood into the pulmonary and systemic
circulation.
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The most important function of the A-V node is
to regulate the timing of the ventricular
contraction by delaying the action potentials.
The delayed action potentials are spread over
the ventricles to cause a contraction.
1.The S-A Node generates an action potential.
2. The action potential propagates in the atria and
causes a contraction. It is also transmitted to
the AV Node.
3.The action potential is delayed at the A-V Node.
4.The action potential is transmitted to the
ventricles and causes a contraction.
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The electrocardiogram (ECG) is a standardized
way to measure and display the electrical
activity of the heart.
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The P Wave: Depolarization of the atria
The QRS Complex: Depolarization of the
ventricles
The T Wave: Repolarization of the ventricles
From one P Wave to the next P wave duration
equals to a cardiac cycle