Liverpool Hospital
Intensive Care: Learning Packages
Intensive Care Unit
Pacemaker Learning Package
LH_ICU2016_Learning_Package_Pacemaker_Learning_Package
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P a g e
3.
Conductivity: the ability to transmit an electrical impulse from one cell
to another.
The electrical current is first initiated in the SA node, the hearts natural
pacemaker, located at the top of the right atrium.
The SA node is composed of nodal cells. In
a normal resting adult heart,
the SA node initiates firing at 60 to100 impulses/minute, but the rate can
change in response to the metabolic demands of the body. The impulses
cause electrical stimulation and subsequent contraction of the atria.
These signals then travel across the atrium to the atrioventricular node,
located close to the septal leaflet of the tricuspid valve.
The AV node is also made up of nodal cells.
The AV node coordinates
these incoming electrical impulses. After a slight delay (giving the atria
time to contract and complete ventricular filling), it relays the impulse to
the ventricles.
The Purkinje cells then take over in the ventricle.
The impulse in the ventricles is initially conducted through a bundle of
specialized conducting tissue called the bundle of His, which then divides
into the right bundle branch (conducting impulses to the right ventricle)
and the left bundle branch (conducting impulses to the left ventricle).
To transmit impulses to the left ventricle, the heart's largest chamber, the
left bundle branch divides into the left anterior
and left posterior bundle
branches.
Impulses travel through the bundle branches to reach the Purkinje fibers
(the terminal point in the conduction system).
The Purkinje cells rapidly conduct the impulses through the thick
walls of
the ventricles. At this point, the myocardial cells are
stimulated, causing
ventricular contraction. (1)