Download The Electrical Conduction of the Heart

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The Electrical
Conduction of the
Heart
The heart is, in the simplest terms, a pump
made up of muscle tissue. Like all pumps, the
heart requires a source of energy and oxygen in
order to function. The hearts pumping action
comes from an intrinsic electrical conduction
system.
This movement of the signals causes the heart to contract
(or beat) and relax. The number of electrical signals controls the speed of your heartbeat. The more signals passing
through the heart, the faster the heartbeat.
Usually, 60-100 signals per minute travel these pathways.
This equates to a heartbeat of 60-100 beats a minute.
Step 1. The S-A node creates an electrical signal
Step 2. The electrical signal follows the natural
electrical pathways through both atria. The
movement of electricity causes the atria to contract, pushing blood into the ventricles
Step 3. The electrical signal reaches the A-V
node. There, the signal pauses to give the ventricles time to fill with blood
Slow Arrhythmias—when the heart beats too slowly it
is called bradycardia (brady=slow cardia=heart). Slow
arrhythmias can be a problem because they cause the
oxygen and nutrient rich blood to travel more slowly to
your organs. Your body may not receive enough oxygen
to function properly, often making you dizzy or breathless.
Fast Arrhythmias-when the heart beats too fast it is
called tachycardia (tachy=fast, cardia=heart). During
tachycardia the heart is not able to pump blood to the
body as well as it should. Fast rhythms in the upper
chambers may not be life-threatening, but may contribute to other problems that are more serious. Fast arrhythmias in the lower chambers, the ventricles, can be
very dangerous, even fatal.
Step 4. The electrical signal spreads through the
His-Purkinje system. The movement of electricity causes the ventricles to contract, pushing
blood to your lungs and body.
Parts of the Electrical System
Your hearts electrical system includes 3 important parts
S-A node (sinoatrial node)-known as the hearts
natural pacemaker. The S-A node initiates each
heartbeat
A-V node (atrioventricular node) - the bridge between the atria and the ventricles. Electrical signals
are passed from the atria down to the ventricles
through the A-V node.
His-Purkinje system—carries the electrical signals
throughout the ventricles. The His-Purkinje system
consists of the following parts:
1. His Bundle (the start of the system)
2. Right Bundle Branch
3. Left Bundle Branch (2 Tracts)
4. Purkinje fibers (the end of the system)
Note that the atria contract a fraction of a second before
the ventricles do. After your heart contracts, it relaxes for
a moment before the process begins again.
When working correctly, your conduction system automatically responds to your body's changing need for oxygen:
When you climb stairs, carry heavy groceries, or take
a walk, you need more oxygen, therefore your heart
beats at a faster heart rate.
When you are sitting or sleeping, you need less oxygen, therefore your heart beats at a slower rate.
When your heart doesn’t work as it should
The Path of an electrical signal
Sometimes there are problems with the electrical conduction system:
The S-A node doesn’t produce the right number of
signals
Another part of your heart takes over as the natural
pacemaker
The electrical pathways are interrupted
A system of electrical pathways in your heart connects
one part to another the S-A node to the A-V node for
instance.
Sometimes the heart beats too slowly or too rapidly.
Heartbeats that are too fast or too slow are called arrhythmias.
What causes these problems?
Interruptions in the pathways can occur for a number of
reasons:
Heart disease causes changes in the heart tissue
Ageing of the heart muscle can also change the
heart tissue
Infection and scarring
Physical problems such as diabetes, smoking, high
blood pressure, and excessive alcohol or drug use,
can affect the heart tissue.
Inherited heart problems
Evidence of heart failure or a heart attack
People who have had a heart attack or have heart failure
often have hearts that don’t pump blood as well as they
should. The Ejection Fraction (EF) is a measurement
of how well the heart is pumping. A low EF also may
mean that these people are at a higher risk for arrhythmia.