200080.vtt
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WEBVTT
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A network of specialized muscle cells
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is found in the heart's walls.
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These muscle cells send signals to
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the rest of the heart muscle
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causing a contraction.
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This group of muscle cells is
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called the cardiac conduction system.
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The main parts of the system
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are the SA node, AV node,
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bundle of His, bundle branches,
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and Purkinje fibers.
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Let's follow a signal
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through the contraction process.
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The SA node starts the sequence by causing
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the atrial muscles to contract.
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That's why doctors
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sometimes call it the anatomical pacemaker.
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Next, the signal travels to the AV node,
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through the bundle of His,
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down the bundle branches,
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and through the Purkinje fibers,
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causing the ventricles to contract.
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This signal creates an electrical current that
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can be seen on a graph
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called an electrocardiogram, or EKG.
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Doctors use an EKG to see how well
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the cardiac conduction system works.
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Any changes on the EKG
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can mean serious problems.