Pacemaker Tissues of the Heart
Pacemaker produces impulses to trigger heartbeats.
Cells of the pacemaker tissue depolarize spontaneously → fire action potential at regular intervals. This firing rate is different for different pacemaker tissues.
Following tissues have pacemaker activity:
SA Node (Sinoatrial Node): Firing rate 70-80 /min
AV Node (Atrioventricular Node): Firing rate 40 /min
Purkinje Fibers: Firing rate 20 impulses/min
The fastest pacemaker tissue dominates the others
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Sets the pace of the heart
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As SA node is the fastest among all
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Normally the pacemaker of heart is SA node
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SA node is called primary pacemaker of the heart
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If SA node does not function properly
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The next fastest tissue i.e. AV node becomes the pacemaker
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AV node is called secondary pacemaker of the heart
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If AV node also fails
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Purkinje fibers set the pace
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Purkinje fibers are called tertiary pacemaker
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However Purkinje fibers are very slow and not reliable as pacemaker
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Might need to implant artificial pacemaker