<s>
The	O
cardiac	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
(	O
CCS	O
)	O
(	O
also	O
called	O
the	O
electrical	O
conduction	B-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
)	O
transmits	O
the	O
signals	B-Algorithm
generated	O
by	O
the	O
sinoatrial	O
node	O
–	O
the	O
heart	O
's	O
pacemaker	B-Device
,	O
to	O
cause	O
the	O
heart	O
muscle	O
to	O
contract	O
,	O
and	O
pump	O
blood	O
through	O
the	O
body	O
's	O
circulatory	O
system	O
.	O
</s>
<s>
The	O
pacemaking	B-Algorithm
signal	O
travels	O
through	O
the	O
right	O
atrium	O
to	O
the	O
atrioventricular	O
node	O
,	O
along	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
and	O
through	O
the	O
bundle	O
branches	O
to	O
Purkinje	B-Algorithm
fibers	I-Algorithm
in	O
the	O
walls	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
The	O
Purkinje	B-Algorithm
fibers	I-Algorithm
transmit	O
the	O
signals	B-Algorithm
more	O
rapidly	O
to	O
stimulate	O
contraction	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
The	O
conduction	B-Algorithm
system	I-Algorithm
consists	O
of	O
specialized	O
heart	O
muscle	O
cells	O
,	O
situated	O
within	O
the	O
myocardium	O
.	O
</s>
<s>
There	O
is	O
a	O
skeleton	O
of	O
fibrous	O
tissue	O
that	O
surrounds	O
the	O
conduction	B-Algorithm
system	I-Algorithm
which	O
can	O
be	O
seen	O
on	O
an	O
ECG	B-Application
.	O
</s>
<s>
Dysfunction	O
of	O
the	O
conduction	B-Algorithm
system	I-Algorithm
can	O
cause	O
irregular	B-Application
heart	I-Application
rhythms	I-Application
including	O
rhythms	O
that	O
are	O
too	B-Application
fast	I-Application
or	O
too	B-Algorithm
slow	I-Algorithm
.	O
</s>
<s>
Electrical	O
signals	B-Algorithm
arising	O
in	O
the	O
SA	O
node	O
(	O
located	O
in	O
the	O
right	O
atrium	O
)	O
stimulate	O
the	O
atria	O
to	O
contract	O
.	O
</s>
<s>
Then	O
the	O
signals	B-Algorithm
travel	O
to	O
the	O
atrioventricular	O
node	O
(	O
AV	O
node	O
)	O
,	O
which	O
is	O
located	O
in	O
the	O
interatrial	O
septum	O
.	O
</s>
<s>
After	O
a	O
short	O
delay	O
that	O
gives	O
the	O
ventricles	O
time	O
to	O
fill	O
with	O
blood	O
,	O
the	O
electrical	O
signal	O
diverges	O
and	O
is	O
conducted	O
through	O
the	O
left	O
and	O
right	O
bundle	O
branches	O
of	O
His	B-Algorithm
to	O
the	O
respective	O
Purkinje	B-Algorithm
fibers	I-Algorithm
for	O
each	O
side	O
of	O
the	O
heart	O
,	O
as	O
well	O
as	O
to	O
the	O
endocardium	O
at	O
the	O
apex	O
of	O
the	O
heart	O
,	O
then	O
finally	O
to	O
the	O
ventricular	O
epicardium	O
;	O
causing	O
the	O
ventricles	O
to	O
contract	O
.	O
</s>
<s>
These	O
signals	B-Algorithm
are	O
generated	O
rhythmically	O
,	O
which	O
results	O
in	O
the	O
coordinated	O
rhythmic	O
contraction	O
and	O
relaxation	O
of	O
the	O
heart	O
.	O
</s>
<s>
While	O
advantageous	O
under	O
normal	O
circumstances	O
,	O
this	O
property	O
can	O
be	O
detrimental	O
,	O
as	O
it	O
has	O
potential	O
to	O
allow	O
the	O
propagation	O
of	O
incorrect	O
electrical	O
signals	B-Algorithm
.	O
</s>
<s>
Embryologic	O
evidence	O
of	O
generation	O
of	O
the	O
cardiac	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
illuminates	O
the	O
respective	O
roles	O
of	O
this	O
specialized	O
set	O
of	O
cells	O
.	O
</s>
<s>
The	O
positively	O
charged	O
ions	O
entering	O
the	O
cell	O
cause	O
the	O
depolarization	O
characteristic	O
of	O
an	O
action	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
There	O
are	O
important	O
physiological	O
differences	O
between	O
nodal	O
cells	O
and	O
ventricular	O
cells	O
;	O
the	O
specific	O
differences	O
in	O
ion	O
channels	O
and	O
mechanisms	O
of	O
polarization	O
give	O
rise	O
to	O
unique	O
properties	O
of	O
SA	O
node	O
cells	O
,	O
most	O
importantly	O
the	O
spontaneous	O
depolarizations	O
necessary	O
for	O
the	O
SA	O
node	O
's	O
pacemaker	B-Device
activity	O
.	O
</s>
<s>
In	O
order	O
to	O
maximize	O
efficiency	O
of	O
contractions	O
and	O
cardiac	O
output	O
,	O
the	O
conduction	B-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
has	O
:	O
</s>
<s>
Although	O
the	O
ventricular	O
stimulus	O
originates	O
from	O
the	O
AV	O
node	O
in	O
the	O
wall	O
separating	O
the	O
atria	O
and	O
ventricles	O
,	O
the	O
Bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
conducts	O
the	O
signal	O
to	O
the	O
apex	O
.	O
</s>
<s>
The	O
action	B-Algorithm
potentials	I-Algorithm
of	O
cardiac	O
muscle	O
are	O
unusually	O
sustained	O
.	O
</s>
<s>
An	O
electrocardiogram	B-Application
is	O
a	O
recording	O
of	O
the	O
electrical	O
activity	O
of	O
the	O
heart	O
.	O
</s>
<s>
Under	O
normal	O
conditions	O
,	O
electrical	O
activity	O
is	O
spontaneously	O
generated	O
by	O
the	O
SA	O
node	O
,	O
the	O
cardiac	B-Algorithm
pacemaker	I-Algorithm
.	O
</s>
<s>
The	O
conduction	B-Algorithm
of	O
the	O
electrical	O
impulses	O
throughout	O
the	O
atria	O
is	O
seen	O
on	O
the	O
ECG	B-Application
as	O
the	O
P	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
The	O
AV	O
node	O
functions	O
as	O
a	O
critical	O
delay	O
in	O
the	O
conduction	B-Algorithm
system	I-Algorithm
.	O
</s>
<s>
The	O
delay	O
in	O
the	O
AV	O
node	O
forms	O
much	O
of	O
the	O
PR	O
segment	O
on	O
the	O
ECG	B-Application
,	O
and	O
part	O
of	O
atrial	O
repolarization	O
can	O
be	O
represented	O
by	O
the	O
PR	O
segment	O
.	O
</s>
<s>
The	O
distal	O
portion	O
of	O
the	O
AV	O
node	O
is	O
known	O
as	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
.	O
</s>
<s>
The	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
splits	O
into	O
two	O
branches	O
in	O
the	O
interventricular	O
septum	O
:	O
the	O
left	O
bundle	O
branch	O
and	O
the	O
right	O
bundle	O
branch	O
.	O
</s>
<s>
The	O
two	O
bundle	O
branches	O
taper	O
out	O
to	O
produce	O
numerous	O
Purkinje	B-Algorithm
fibers	I-Algorithm
,	O
which	O
stimulate	O
individual	O
groups	O
of	O
myocardial	O
cells	O
to	O
contract	O
.	O
</s>
<s>
The	O
spread	O
of	O
electrical	O
activity	O
through	O
the	O
ventricular	O
myocardium	O
produces	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Atrial	O
repolarization	O
occurs	O
and	O
is	O
masked	O
during	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
by	O
ventricular	B-Application
depolarization	I-Application
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
In	O
the	O
ECG	B-Application
,	O
repolarization	O
includes	O
the	O
J	O
point	O
,	O
ST	O
segment	O
,	O
and	O
T	O
and	O
U	O
waves	O
.	O
</s>
<s>
The	O
transthoracically	O
measured	O
PQRS	O
portion	O
of	O
an	O
electrocardiogram	B-Application
is	O
chiefly	O
influenced	O
by	O
the	O
sympathetic	O
nervous	O
system	O
.	O
</s>
<s>
An	O
impulse	O
(	O
action	B-Algorithm
potential	I-Algorithm
)	O
that	O
originates	O
from	O
the	O
SA	O
node	O
at	O
a	O
relative	O
rate	O
of	O
60-100bpm	O
is	O
known	O
as	O
a	O
normal	O
sinus	O
rhythm	O
.	O
</s>
<s>
If	O
SA	O
nodal	O
impulses	O
occur	O
at	O
a	O
rate	O
less	O
than	O
60bpm	O
,	O
the	O
heart	B-Algorithm
rhythm	I-Algorithm
is	O
known	O
as	O
sinus	B-Algorithm
bradycardia	I-Algorithm
.	O
</s>
<s>
If	O
SA	O
nodal	O
impulses	O
occur	O
at	O
a	O
rate	O
exceeding	O
100bpm	O
,	O
the	O
consequent	O
rapid	B-Application
heart	I-Application
rate	I-Application
is	O
sinus	B-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
If	O
the	O
SA	O
node	O
fails	O
to	O
initialize	O
,	O
the	O
AV	O
junction	O
can	O
take	O
over	O
as	O
the	O
main	O
pacemaker	B-Device
of	O
the	O
heart	O
.	O
</s>
<s>
The	O
AV	O
junction	O
consists	O
of	O
the	O
AV	O
node	O
,	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
and	O
the	O
surrounding	O
area	O
;	O
it	O
has	O
a	O
regular	O
rate	O
of	O
40	O
to	O
60bpm	O
.	O
</s>
<s>
These	O
"	O
junctional	O
"	O
rhythms	O
are	O
characterized	O
by	O
a	O
missing	O
or	O
inverted	O
P	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
If	O
both	O
the	O
SA	O
node	O
and	O
the	O
AV	O
junction	O
fail	O
to	O
initialize	O
the	O
electrical	O
impulse	O
,	O
the	O
ventricles	O
can	O
fire	O
the	O
electrical	O
impulses	O
themselves	O
at	O
a	O
rate	O
of	O
20	O
to	O
40bpm	O
and	O
will	O
have	O
a	O
QRS	B-Algorithm
complex	I-Algorithm
of	O
greater	O
than	O
120ms	O
.	O
</s>
<s>
An	O
arrhythmia	B-Application
is	O
an	O
abnormal	O
rhythm	O
or	O
speed	O
of	O
rhythm	O
of	O
the	O
heartbeat	O
.	O
</s>
<s>
A	O
slow	B-Algorithm
heart	I-Algorithm
rate	I-Algorithm
of	O
60	O
or	O
less	O
beats	O
per	O
minute	O
is	O
defined	O
as	O
bradycardia	B-Algorithm
.	O
</s>
<s>
A	O
fast	B-Application
heart	I-Application
rate	I-Application
of	O
more	O
than	O
100	O
beats	O
per	O
minute	O
is	O
defined	O
as	O
tachycardia	B-Application
.	O
</s>
<s>
An	O
arrythmia	B-Application
is	O
defined	O
as	O
one	O
that	O
is	O
not	O
physiological	O
such	O
as	O
the	O
lowered	O
heart	O
rate	O
that	O
a	O
trained	O
athlete	O
may	O
naturally	O
have	O
developed	O
;	O
the	O
resting	O
heart	O
rates	O
may	O
be	O
less	O
than	O
60	O
bpm	O
.	O
</s>
<s>
When	O
an	O
arrhythmia	B-Application
cannot	O
be	O
treated	O
by	O
medication	O
an	O
artificial	B-Device
pacemaker	I-Device
may	O
be	O
implanted	O
to	O
control	O
the	O
conduction	B-Algorithm
system	I-Algorithm
.	O
</s>
