Welcome to this video tutorial on the electrical conduction system of the heart.
In this video, we’re going to look at how the rhythm of the heart is controlled by electrical impulses.
The pumping action of the heart is regulated by an electrical conduction system that coordinates
the contractions of the four heart chambers.
Remember, the four chambers include the right atrium, right ventricle, left atrium, and left ventricle.
The cardiac conduction system is a group of specialized muscle cells and conducting fibers
that initiate the normal cardiac cycle and cause the heart to contract.
The heart’s ability to beat all starts in the sinoatrial, or S.A., node,
which is a small mass of specialized tissue located in the atria.
Depolarization, or activation of the cardiac muscle, is initiated by an impulse from the S.A. node.
The impulse spreads through the right atrium and through Bachmann’s bundle to activate the left atrium.
The electrical stimulus generated by the S.A. node
occurs 60-100 times per minute under normal conditions.
Therefore, the S.A. node is often called the natural pacemaker of the heart,
and a normal heart rhythm is called a sinus rhythm.
Once the atria are activated, the impulse moves down the internodal pathways to the
atrioventricular node, the A.V. node.
The A.V. node functions as a critical delay in the conduction system.
This delay prevents the atria and ventricles from contracting at the same time,
which would cause an ineffective flow of blood through the heart.
The impulse then enters the bundle of His and is transmitted along the bundle branches.
The bundle of His splits into two branches in the interventricular septum,
which is just the division between the two ventricles.
The left bundle branch activates the left ventricle, and the right bundle branch activates the right ventricle.
The right and left bundle branches taper out to form many Purkinje fibers,
activating the ventricular walls almost simultaneously.
The ventricular activation continues from the apex back toward the base of the heart
to complete the process of ventricular contraction.
Remember, depolarization refers to the activation of the heart muscle, or contraction, and repolarization
refers to the muscle cells returning to a resting state.
Let’s review the heart’s electrical impulse in 5 easy steps.
First, the impulse leaves the S.A. node, signaling the atria to contract.
Then it travels down the internodal pathways to the A.V. node.
Then it travels to the bundle of His, where it divides into the right and left bundle branches.
It then moves on to the Purkinje fibers, causing the ventricles to contract.
Here are some important points to remember:
The S.A., or sinoatrial, node is the pacemaker of the heart.
It initiates atriocontraction, or depolarization.
It causes a stimulus 60-100 times per minute.
It causes the contraction of the atria and is represented by the P wave on the EKG.
The A.V., or atrioventricular node, is the gatekeeper of the heart.
It functions as a slight delay to allow all blood from the atria to empty into the ventricles
and prevent any backflow.
It beats at 40-60 beats per minute.
The bundle of His branches off into right and left bundles to the Purkinje fibers.
It causes the depolarization, or contraction, of the ventricles.
The Purkinje fibers fire at a rate of 20-40 beats per minute.
The contraction of the ventricles is shown as the QRS complex on the EKG.
Finally, the ventricles must return to the resting state, which is called ventricular repolarization
and is represented by the T wave on the EKG.
Thank you for watching this video tutorial on the electrical conduction system of the heart!
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