<s>
Arrhythmias	B-Application
,	O
also	O
known	O
as	O
cardiac	B-Application
arrhythmias	I-Application
,	O
heart	B-Application
arrhythmias	I-Application
,	O
or	O
dysrhythmias	O
,	O
are	O
irregularities	O
in	O
the	O
heartbeat	O
,	O
including	O
when	O
it	O
is	O
too	O
fast	O
or	O
too	O
slow	O
.	O
</s>
<s>
A	O
resting	O
heart	O
rate	O
that	O
is	O
too	O
fast	O
–	O
above	O
100	O
beats	O
per	O
minute	O
in	O
adults	O
–	O
is	O
called	O
tachycardia	B-Application
,	O
and	O
a	O
resting	O
heart	O
rate	O
that	O
is	O
too	O
slow	O
–	O
below	O
60	O
beats	O
per	O
minute	O
–	O
is	O
called	O
bradycardia	B-Algorithm
.	O
</s>
<s>
Some	O
types	O
of	O
arrhythmias	B-Application
have	O
no	O
symptoms	O
.	O
</s>
<s>
Symptoms	O
,	O
when	O
present	O
,	O
may	O
include	O
palpitations	B-Algorithm
or	O
feeling	O
a	O
pause	O
between	O
heartbeats	O
.	O
</s>
<s>
While	O
most	O
cases	O
of	O
arrhythmia	B-Application
are	O
not	O
serious	O
,	O
some	O
predispose	O
a	O
person	O
to	O
complications	O
such	O
as	O
stroke	O
or	O
heart	O
failure	O
.	O
</s>
<s>
Arrhythmias	B-Application
are	O
often	O
categorized	O
into	O
four	O
groups	O
:	O
extra	B-Algorithm
beats	I-Algorithm
,	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
,	O
ventricular	O
arrhythmias	B-Application
and	O
bradyarrhythmias	B-Algorithm
.	O
</s>
<s>
Extra	B-Algorithm
beats	I-Algorithm
include	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
,	O
premature	B-Error_Name
ventricular	I-Error_Name
contractions	I-Error_Name
and	O
premature	B-Algorithm
junctional	I-Algorithm
contractions	I-Algorithm
.	O
</s>
<s>
Supraventricular	B-Algorithm
tachycardias	I-Algorithm
include	O
atrial	B-Application
fibrillation	I-Application
,	O
atrial	O
flutter	O
and	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
Ventricular	O
arrhythmias	B-Application
include	O
ventricular	O
fibrillation	O
and	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
Bradyarrhythmias	B-Algorithm
are	O
due	O
to	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
or	O
atrioventricular	B-Algorithm
conduction	I-Algorithm
disturbances	I-Algorithm
.	O
</s>
<s>
Arrhythmias	B-Application
are	O
due	O
to	O
problems	O
with	O
the	O
electrical	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
.	O
</s>
<s>
A	O
number	O
of	O
tests	O
can	O
help	O
with	O
diagnosis	O
,	O
including	O
an	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
and	O
Holter	O
monitor	O
.	O
</s>
<s>
Many	O
arrhythmias	B-Application
can	O
be	O
effectively	O
treated	O
.	O
</s>
<s>
Treatments	O
may	O
include	O
medications	O
,	O
medical	O
procedures	O
such	O
as	O
inserting	O
a	O
pacemaker	B-Device
,	O
and	O
surgery	O
.	O
</s>
<s>
Medications	O
for	O
a	O
fast	B-Application
heart	I-Application
rate	I-Application
may	O
include	O
beta	O
blockers	O
,	O
or	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
such	O
as	O
procainamide	O
,	O
which	O
attempt	O
to	O
restore	O
a	O
normal	O
heart	B-Algorithm
rhythm	I-Algorithm
.	O
</s>
<s>
Pacemakers	B-Device
are	O
often	O
used	O
for	O
slow	B-Algorithm
heart	I-Algorithm
rates	I-Algorithm
.	O
</s>
<s>
Those	O
with	O
an	O
irregular	B-Application
heartbeat	I-Application
are	O
often	O
treated	O
with	O
blood	O
thinners	O
to	O
reduce	O
the	O
risk	O
of	O
complications	O
.	O
</s>
<s>
Those	O
who	O
have	O
severe	O
symptoms	O
from	O
an	O
arrhythmia	B-Application
or	O
are	O
medically	O
unstable	O
may	O
receive	O
urgent	O
treatment	O
with	O
a	O
controlled	O
electric	O
shock	O
in	O
the	O
form	O
of	O
cardioversion	O
or	O
defibrillation	O
.	O
</s>
<s>
Arrhythmia	B-Application
affects	O
millions	O
of	O
people	O
.	O
</s>
<s>
In	O
Europe	O
and	O
North	O
America	O
,	O
as	O
of	O
2014	O
,	O
atrial	B-Application
fibrillation	I-Application
affects	O
about	O
2%	O
to	O
3%	O
of	O
the	O
population	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
and	O
atrial	O
flutter	O
resulted	O
in	O
112,000	O
deaths	O
in	O
2013	O
,	O
up	O
from	O
29,000	O
in	O
1990	O
.	O
</s>
<s>
However	O
,	O
in	O
most	O
recent	O
cases	O
concerning	O
the	O
SARS-CoV	O
‑2	O
pandemic	O
,	O
cardiac	B-Application
arrhythmias	I-Application
are	O
commonly	O
developed	O
and	O
associated	O
with	O
high	O
morbidity	O
and	O
mortality	O
among	O
patients	O
hospitalized	O
with	O
the	O
COVID-19	O
infection	O
,	O
due	O
to	O
the	O
infection	O
's	O
ability	O
to	O
cause	O
myocardial	O
injury	O
.	O
</s>
<s>
About	O
80%	O
of	O
sudden	O
cardiac	O
death	O
is	O
the	O
result	O
of	O
ventricular	O
arrhythmias	B-Application
.	O
</s>
<s>
Arrhythmias	B-Application
may	O
occur	O
at	O
any	O
age	O
but	O
are	O
more	O
common	O
among	O
older	O
people	O
.	O
</s>
<s>
Arrhythmias	B-Application
may	O
also	O
occur	O
in	O
children	O
;	O
however	O
,	O
the	O
normal	O
range	O
for	O
the	O
heart	O
rate	O
varies	O
with	O
age	O
.	O
</s>
<s>
Arrhythmia	B-Application
may	O
be	O
classified	O
by	O
rate	O
(	O
tachycardia	B-Application
,	O
bradycardia	B-Algorithm
)	O
,	O
mechanism	O
(	O
automaticity	O
,	O
re-entry	O
,	O
triggered	O
)	O
or	O
duration	O
(	O
isolated	O
premature	B-Algorithm
beats	I-Algorithm
;	O
couplets	O
;	O
runs	O
,	O
that	O
is	O
3	O
or	O
more	O
beats	O
;	O
non-sustained	O
=	O
less	O
than	O
30	O
seconds	O
or	O
sustained	O
=	O
over	O
30	O
seconds	O
)	O
.	O
</s>
<s>
Arrhythmias	B-Application
are	O
also	O
classified	O
by	O
site	O
of	O
origin	O
:	O
</s>
<s>
Groups	O
of	O
three	O
premature	B-Error_Name
ventricular	I-Error_Name
beats	I-Error_Name
are	O
called	O
triplets	O
and	O
are	O
considered	O
a	O
brief	O
run	O
of	O
non-sustained	O
ventricular	O
tachycardia	O
(	O
NSVT	B-Application
)	O
;	O
if	O
the	O
grouping	O
lasts	O
for	O
more	O
than	O
30	O
seconds	O
,	O
it	O
is	O
considered	O
sustained	B-Application
ventricular	I-Application
tachycardia	I-Application
(	O
VT	O
)	O
.	O
</s>
<s>
These	O
are	O
also	O
known	O
as	O
AV	B-Algorithm
blocks	I-Algorithm
,	O
because	O
the	O
vast	O
majority	O
of	O
them	O
arise	O
from	O
pathology	O
at	O
the	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
They	O
are	O
the	O
most	O
common	O
causes	O
of	O
bradycardia	B-Algorithm
:	O
</s>
<s>
First	O
,	O
second	O
,	O
and	O
third-degree	B-Architecture
blocks	I-Architecture
also	O
can	O
occur	O
at	O
the	O
level	O
of	O
the	O
sinoatrial	O
junction	O
.	O
</s>
<s>
This	O
is	O
referred	O
to	O
as	O
sinoatrial	B-Algorithm
block	I-Algorithm
typically	O
manifesting	O
with	O
various	O
degrees	O
and	O
patterns	O
of	O
sinus	B-Algorithm
bradycardia	I-Algorithm
.	O
</s>
<s>
Sudden	O
arrhythmic	O
death	O
syndrome	O
(	O
SADS	O
)	O
,	O
is	O
a	O
term	O
used	O
as	O
part	O
of	O
sudden	O
unexpected	O
death	O
syndrome	O
to	O
describe	O
sudden	O
death	O
because	O
of	O
cardiac	O
arrest	O
occasioned	O
by	O
an	O
arrhythmia	B-Application
in	O
the	O
presence	O
or	O
absence	O
of	O
any	O
structural	O
heart	O
disease	O
on	O
autopsy	O
.	O
</s>
<s>
Causes	O
of	O
SADS	O
in	O
young	O
people	O
include	O
viral	O
myocarditis	O
,	O
long	O
QT	O
syndrome	O
,	O
Brugada	O
syndrome	O
,	O
Catecholaminergic	O
polymorphic	B-Application
ventricular	I-Application
tachycardia	I-Application
,	O
hypertrophic	O
cardiomyopathy	O
and	O
arrhythmogenic	B-Application
right	O
ventricular	O
dysplasia	O
.	O
</s>
<s>
Arrhythmias	B-Application
may	O
also	O
occur	O
in	O
the	O
fetus	O
.	O
</s>
<s>
Any	O
rhythm	O
beyond	O
these	O
limits	O
is	O
abnormal	O
and	O
classed	O
as	O
a	O
fetal	O
arrhythmia	B-Application
.	O
</s>
<s>
These	O
are	O
mainly	O
the	O
result	O
of	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
,	O
usually	O
give	O
no	O
symptoms	O
,	O
and	O
have	O
little	O
consequence	O
.	O
</s>
<s>
The	O
term	O
cardiac	B-Application
arrhythmia	I-Application
covers	O
a	O
very	O
large	O
number	O
of	O
very	O
different	O
conditions	O
.	O
</s>
<s>
The	O
most	O
common	O
symptom	O
of	O
arrhythmia	B-Application
is	O
an	O
awareness	O
of	O
an	O
abnormal	O
heartbeat	O
,	O
called	O
palpitations	B-Algorithm
.	O
</s>
<s>
Some	O
of	O
these	O
arrhythmias	B-Application
are	O
harmless	O
(	O
though	O
distracting	O
for	O
patients	O
)	O
but	O
some	O
of	O
them	O
predispose	O
to	O
adverse	O
outcomes	O
.	O
</s>
<s>
Some	O
arrhythmias	B-Application
do	O
not	O
cause	O
symptoms	O
and	O
are	O
not	O
associated	O
with	O
increased	O
mortality	O
.	O
</s>
<s>
However	O
,	O
some	O
asymptomatic	O
arrhythmias	B-Application
are	O
associated	O
with	O
adverse	O
events	O
.	O
</s>
<s>
If	O
an	O
arrhythmia	B-Application
results	O
in	O
a	O
heartbeat	O
that	O
is	O
too	O
fast	O
,	O
too	O
slow	O
,	O
or	O
too	O
weak	O
to	O
supply	O
the	O
body	O
's	O
needs	O
,	O
this	O
manifests	O
as	O
lower	O
blood	O
pressure	O
and	O
may	O
cause	O
lightheadedness	O
,	O
dizziness	O
,	O
syncope	O
or	O
brain	O
death	O
due	O
to	O
insufficient	O
supply	O
of	O
blood	O
to	O
the	O
brain	O
.	O
</s>
<s>
Some	O
types	O
of	O
arrhythmia	B-Application
result	O
in	O
cardiac	O
arrest	O
,	O
or	O
sudden	O
death	O
.	O
</s>
<s>
Medical	O
assessment	O
of	O
the	O
abnormality	O
using	O
an	O
electrocardiogram	B-Application
is	O
one	O
way	O
to	O
diagnose	O
and	O
assess	O
the	O
risk	O
of	O
any	O
given	O
arrhythmia	B-Application
.	O
</s>
<s>
Cardiac	B-Application
arrhythmia	I-Application
are	O
caused	O
by	O
one	O
of	O
two	O
major	O
mechanism	O
.	O
</s>
<s>
The	O
first	O
of	O
arrhythmia	B-Application
is	O
a	O
result	O
of	O
enhanced	O
or	O
abnormal	O
impulse	B-Algorithm
formation	O
originating	O
at	O
the	O
pacemaker	B-Device
or	O
the	O
His-Purkinje	O
network	O
.	O
</s>
<s>
The	O
second	O
is	O
due	O
to	O
re-entry	O
conduction	B-Algorithm
disturbances	O
.	O
</s>
<s>
Cardiac	B-Application
arrhythmia	I-Application
is	O
often	O
first	O
detected	O
by	O
simple	O
but	O
nonspecific	O
means	O
:	O
auscultation	O
of	O
the	O
heartbeat	O
with	O
a	O
stethoscope	O
,	O
or	O
feeling	O
for	O
peripheral	O
pulses	O
.	O
</s>
<s>
These	O
cannot	O
usually	O
diagnose	O
specific	O
arrhythmia	B-Application
but	O
can	O
give	O
a	O
general	O
indication	O
of	O
the	O
heart	O
rate	O
and	O
whether	O
it	O
is	O
regular	O
or	O
irregular	O
.	O
</s>
<s>
Not	O
all	O
the	O
electrical	O
impulses	O
of	O
the	O
heart	O
produce	O
audible	O
or	O
palpable	O
beats	O
;	O
in	O
many	O
cardiac	B-Application
arrhythmias	I-Application
,	O
the	O
premature	O
or	O
abnormal	O
beats	O
do	O
not	O
produce	O
an	O
effective	O
pumping	O
action	O
and	O
are	O
experienced	O
as	O
"	O
skipped	O
"	O
beats	O
.	O
</s>
<s>
The	O
simplest	O
specific	O
diagnostic	O
test	O
for	O
assessment	O
of	O
heart	B-Algorithm
rhythm	I-Algorithm
is	O
the	O
electrocardiogram	B-Application
(	O
abbreviated	O
ECG	B-Application
or	O
EKG	B-Application
)	O
.	O
</s>
<s>
A	O
Holter	O
monitor	O
is	O
an	O
EKG	B-Application
recorded	O
over	O
a	O
24-hour	O
period	O
,	O
to	O
detect	O
arrhythmias	B-Application
that	O
may	O
happen	O
briefly	O
and	O
unpredictably	O
throughout	O
the	O
day	O
.	O
</s>
<s>
A	O
more	O
advanced	O
study	O
of	O
the	O
heart	O
's	O
electrical	O
activity	O
can	O
be	O
performed	O
to	O
assess	O
the	O
source	O
of	O
the	O
aberrant	B-Algorithm
heart	O
beats	O
.	O
</s>
<s>
This	O
can	O
be	O
accomplished	O
in	O
an	O
electrophysiology	B-Algorithm
study	I-Algorithm
,	O
an	O
endovascular	O
procedure	O
that	O
uses	O
a	O
catheter	O
to	O
"	O
listen	O
"	O
to	O
the	O
electrical	O
activity	O
from	O
within	O
the	O
heart	O
,	O
additionally	O
if	O
the	O
source	O
of	O
the	O
arrhythmias	B-Application
is	O
found	O
,	O
often	O
the	O
abnormal	O
cells	O
can	O
be	O
ablated	O
and	O
the	O
arrhythmia	B-Application
can	O
be	O
permanently	O
corrected	O
.	O
</s>
<s>
Transesophageal	O
atrial	O
stimulation	O
can	O
differentiate	O
between	O
atrial	O
flutter	O
,	O
AV	B-Algorithm
nodal	I-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
and	O
orthodromic	O
atrioventricular	B-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
It	O
can	O
also	O
evaluate	O
the	O
risk	O
in	O
people	O
with	O
Wolff	O
–	O
Parkinson	O
–	O
White	O
syndrome	O
,	O
as	O
well	O
as	O
terminate	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
caused	O
by	O
re-entry	O
.	O
</s>
<s>
Each	O
heartbeat	O
originates	O
as	O
an	O
electrical	O
impulse	B-Algorithm
from	O
a	O
small	O
area	O
of	O
tissue	O
in	O
the	O
right	O
atrium	O
of	O
the	O
heart	O
called	O
the	O
sinus	O
node	O
or	O
sinoatrial	O
node	O
(	O
SA	O
node	O
)	O
.	O
</s>
<s>
The	O
impulse	B-Algorithm
initially	O
causes	O
both	O
atria	O
to	O
contract	O
,	O
then	O
activates	O
the	O
atrioventricular	B-Algorithm
node	O
(	O
AV	O
node	O
)	O
,	O
which	O
is	O
normally	O
the	O
only	O
electrical	O
connection	O
between	O
the	O
atria	O
and	O
the	O
ventricles	O
(	O
main	O
pumping	O
chambers	O
)	O
.	O
</s>
<s>
The	O
impulse	B-Algorithm
then	O
spreads	O
through	O
both	O
ventricles	O
via	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
and	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
causing	O
a	O
synchronized	O
contraction	O
of	O
the	O
heart	O
muscle	O
and	O
,	O
thus	O
,	O
the	O
pulse	O
.	O
</s>
<s>
The	O
term	O
sinus	B-Algorithm
arrhythmia	I-Algorithm
refers	O
to	O
a	O
normal	O
phenomenon	O
of	O
alternating	O
mild	O
acceleration	O
and	O
slowing	O
of	O
the	O
heart	O
rate	O
that	O
occurs	O
with	O
breathing	O
in	O
and	O
out	O
respectively	O
.	O
</s>
<s>
A	O
slow	O
rhythm	O
(	O
less	O
than	O
60	O
beats/min	O
)	O
is	O
labelled	O
bradycardia	B-Algorithm
.	O
</s>
<s>
This	O
may	O
be	O
caused	O
by	O
a	O
slowed	O
signal	O
from	O
the	O
sinus	O
node	O
(	O
sinus	B-Algorithm
bradycardia	I-Algorithm
)	O
,	O
by	O
a	O
pause	O
in	O
the	O
normal	O
activity	O
of	O
the	O
sinus	O
node	O
(	O
sinus	O
arrest	O
)	O
,	O
or	O
by	O
blocking	O
of	O
the	O
electrical	O
impulse	B-Algorithm
on	O
its	O
way	O
from	O
the	O
atria	O
to	O
the	O
ventricles	O
(	O
AV	B-Algorithm
block	I-Algorithm
or	O
heart	O
block	O
)	O
.	O
</s>
<s>
It	O
may	O
be	O
caused	O
by	O
reversible	O
poisoning	O
of	O
the	O
AV	O
node	O
(	O
with	O
drugs	O
that	O
impair	O
conduction	B-Algorithm
)	O
or	O
by	O
irreversible	O
damage	O
to	O
the	O
node	O
.	O
</s>
<s>
Bradycardias	B-Algorithm
may	O
also	O
be	O
present	O
in	O
the	O
normally	O
functioning	O
heart	O
of	O
endurance	O
athletes	O
or	O
other	O
well-conditioned	O
persons	O
.	O
</s>
<s>
Bradycardia	B-Algorithm
may	O
also	O
occur	O
in	O
some	B-Algorithm
types	I-Algorithm
of	I-Algorithm
seizures	I-Algorithm
.	O
</s>
<s>
In	O
adults	O
and	O
children	O
over	O
15	O
,	O
resting	O
heart	O
rate	O
faster	O
than	O
100	O
beats	O
per	O
minute	O
is	O
labeled	O
tachycardia	B-Application
.	O
</s>
<s>
Tachycardia	B-Application
may	O
result	O
in	O
palpitation	B-Algorithm
;	O
however	O
,	O
tachycardia	B-Application
is	O
not	O
necessarily	O
an	O
arrhythmia	B-Application
.	O
</s>
<s>
Increased	B-Application
heart	I-Application
rate	I-Application
is	O
a	O
normal	O
response	O
to	O
physical	O
exercise	O
or	O
emotional	O
stress	O
.	O
</s>
<s>
This	O
is	O
mediated	O
by	O
the	O
sympathetic	O
nervous	O
system	O
on	O
the	O
sinus	O
node	O
and	O
called	O
sinus	B-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
Other	O
conditions	O
that	O
increase	O
sympathetic	O
nervous	O
system	O
activity	O
in	O
the	O
heart	O
include	O
ingested	O
or	O
injected	O
substances	O
,	O
such	O
as	O
caffeine	B-Application
or	O
amphetamines	O
,	O
and	O
an	O
overactive	O
thyroid	O
gland	O
(	O
hyperthyroidism	O
)	O
or	O
anemia	O
.	O
</s>
<s>
Tachycardia	B-Application
that	O
is	O
not	O
sinus	B-Algorithm
tachycardia	I-Algorithm
usually	O
results	O
from	O
the	O
addition	O
of	O
abnormal	O
impulses	O
to	O
the	O
normal	O
cardiac	O
cycle	O
.	O
</s>
<s>
Although	O
the	O
term	O
"	O
tachycardia	B-Application
"	O
has	O
been	O
known	O
for	O
over	O
160	O
years	O
,	O
bases	O
for	O
the	O
classification	O
of	O
arrhythmias	B-Application
are	O
still	O
being	O
discussed	O
.	O
</s>
<s>
Problems	O
with	O
the	O
electrical	O
pathway	O
of	O
the	O
heart	O
can	O
cause	O
very	O
fast	O
or	O
even	O
deadly	O
arrhythmias	B-Application
.	O
</s>
<s>
This	O
tissue	O
allows	O
the	O
electrical	O
impulse	B-Algorithm
,	O
which	O
stimulates	O
the	O
heartbeat	O
,	O
to	O
happen	O
very	O
rapidly	O
.	O
</s>
<s>
Right	O
ventricular	O
outflow	O
tract	O
tachycardia	B-Application
is	O
the	O
most	O
common	O
type	O
of	O
ventricular	B-Application
tachycardia	I-Application
in	O
otherwise	O
healthy	O
individuals	O
.	O
</s>
<s>
When	O
the	O
node	O
is	O
stimulated	O
,	O
the	O
patient	O
will	O
go	O
into	O
ventricular	B-Application
tachycardia	I-Application
,	O
which	O
does	O
not	O
allow	O
the	O
heart	O
to	O
fill	O
with	O
blood	O
before	O
beating	O
again	O
.	O
</s>
<s>
Automaticity	O
refers	O
to	O
a	O
cardiac	O
muscle	O
cell	O
firing	O
off	O
an	O
impulse	B-Algorithm
on	O
its	O
own	O
.	O
</s>
<s>
All	O
of	O
the	O
cells	O
in	O
the	O
heart	O
have	O
the	O
ability	O
to	O
initiate	O
an	O
action	B-Algorithm
potential	I-Algorithm
;	O
however	O
,	O
only	O
some	O
of	O
these	O
cells	O
are	O
designed	O
to	O
routinely	O
trigger	O
heartbeats	O
.	O
</s>
<s>
These	O
cells	O
are	O
found	O
in	O
the	O
conduction	B-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
and	O
include	O
the	O
SA	O
node	O
,	O
AV	O
node	O
,	O
Bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
and	O
Purkinje	B-Algorithm
fibers	I-Algorithm
.	O
</s>
<s>
The	O
sinoatrial	O
node	O
is	O
a	O
single	O
specialized	O
location	O
in	O
the	O
atrium	O
that	O
has	O
a	O
higher	O
automaticity	O
(	O
a	O
faster	O
pacemaker	B-Device
)	O
than	O
the	O
rest	O
of	O
the	O
heart	O
and	O
,	O
therefore	O
,	O
is	O
usually	O
responsible	O
for	O
setting	O
the	O
heart	O
rate	O
and	O
initiating	O
each	O
heartbeat	O
.	O
</s>
<s>
Any	O
part	O
of	O
the	O
heart	O
that	O
initiates	O
an	O
impulse	B-Algorithm
without	O
waiting	O
for	O
the	O
sinoatrial	O
node	O
is	O
called	O
an	O
ectopic	B-Algorithm
focus	I-Algorithm
and	O
is	O
,	O
by	O
definition	O
,	O
a	O
pathological	O
phenomenon	O
.	O
</s>
<s>
This	O
may	O
cause	O
a	O
single	O
premature	B-Algorithm
beat	I-Algorithm
now	O
and	O
then	O
,	O
or	O
,	O
if	O
the	O
ectopic	B-Algorithm
focus	I-Algorithm
fires	O
more	O
often	O
than	O
the	O
sinoatrial	O
node	O
,	O
it	O
can	O
produce	O
a	O
sustained	O
abnormal	O
rhythm	O
.	O
</s>
<s>
Rhythms	O
produced	O
by	O
an	O
ectopic	B-Algorithm
focus	I-Algorithm
in	O
the	O
atria	O
,	O
or	O
by	O
the	O
atrioventricular	B-Algorithm
node	O
,	O
are	O
the	O
least	O
dangerous	O
dysrhythmias	O
;	O
but	O
they	O
can	O
still	O
produce	O
a	O
decrease	O
in	O
the	O
heart	O
's	O
pumping	O
efficiency	O
because	O
the	O
signal	O
reaches	O
the	O
various	O
parts	O
of	O
the	O
heart	O
muscle	O
with	O
different	O
timing	O
than	O
usual	O
and	O
can	O
be	O
responsible	O
for	O
poorly	O
coordinated	O
contraction	O
.	O
</s>
<s>
The	O
resulting	O
heart	B-Algorithm
rhythm	I-Algorithm
depends	O
on	O
where	O
the	O
first	O
signal	O
begins	O
:	O
If	O
it	O
is	O
the	O
sinoatrial	O
node	O
,	O
the	O
rhythm	O
remains	O
normal	O
but	O
rapid	O
;	O
if	O
it	O
is	O
an	O
ectopic	B-Algorithm
focus	I-Algorithm
,	O
many	O
types	O
of	O
dysrhythmia	O
may	O
ensue	O
.	O
</s>
<s>
Re-entrant	O
arrhythmias	B-Application
occur	O
when	O
an	O
electrical	O
impulse	B-Algorithm
recurrently	O
travels	O
in	O
a	O
tight	O
circle	O
within	O
the	O
heart	O
,	O
rather	O
than	O
moving	O
from	O
one	O
end	O
of	O
the	O
heart	O
to	O
the	O
other	O
and	O
then	O
stopping	O
.	O
</s>
<s>
Normally	O
,	O
the	O
action	B-Algorithm
potential	I-Algorithm
impulse	B-Algorithm
will	O
spread	O
through	O
the	O
heart	O
quickly	O
enough	O
that	O
each	O
cell	O
will	O
respond	O
only	O
once	O
.	O
</s>
<s>
However	O
,	O
if	O
there	O
is	O
some	O
essential	O
heterogeneity	O
of	O
refractory	O
period	O
or	O
if	O
conduction	B-Algorithm
is	O
abnormally	O
slow	O
in	O
some	O
areas	O
(	O
for	O
example	O
in	O
heart	O
damage	O
)	O
so	O
the	O
myocardial	O
cells	O
are	O
unable	O
to	O
activate	O
the	O
fast	O
sodium	O
channel	O
,	O
part	O
of	O
the	O
impulse	B-Algorithm
will	O
arrive	O
late	O
and	O
potentially	O
be	O
treated	O
as	O
a	O
new	O
impulse	B-Algorithm
.	O
</s>
<s>
As	O
a	O
sort	O
of	O
re-entry	O
,	O
vortices	O
of	O
excitation	O
in	O
the	O
myocardium	O
(	O
autowave	O
vortices	O
)	O
are	O
considered	O
to	O
be	O
the	O
main	O
mechanism	O
of	O
life-threatening	O
cardiac	B-Application
arrhythmias	I-Application
.	O
</s>
<s>
Re-entry	O
is	O
also	O
responsible	O
for	O
most	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
,	O
and	O
dangerous	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
These	O
types	O
of	O
re-entry	O
circuits	O
are	O
different	O
from	O
WPW	O
syndromes	O
,	O
which	O
utilize	O
abnormal	O
conduction	B-Algorithm
pathways	I-Algorithm
.	O
</s>
<s>
Although	O
omega-3	O
fatty	O
acids	O
from	O
fish	O
oil	O
can	O
be	O
protective	O
against	O
arrhythmias	B-Application
,	O
they	O
can	O
facilitate	O
re-entrant	O
arrhythmias	B-Application
.	O
</s>
<s>
Fibrillation	O
can	O
affect	O
the	O
atrium	O
(	O
atrial	B-Application
fibrillation	I-Application
)	O
or	O
the	O
ventricle	O
(	O
ventricular	O
fibrillation	O
)	O
:	O
ventricular	O
fibrillation	O
is	O
imminently	O
life-threatening	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
affects	O
the	O
upper	O
chambers	O
of	O
the	O
heart	O
,	O
known	O
as	O
the	O
atria	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
may	O
be	O
due	O
to	O
serious	O
underlying	O
medical	O
conditions	O
and	O
should	O
be	O
evaluated	O
by	O
a	O
physician	O
.	O
</s>
<s>
CPR	O
can	O
prolong	O
the	O
survival	O
of	O
the	O
brain	O
in	O
the	O
lack	O
of	O
a	O
normal	O
pulse	O
,	O
but	O
defibrillation	O
is	O
the	O
only	O
intervention	O
that	O
can	O
restore	O
a	O
healthy	O
heart	B-Algorithm
rhythm	I-Algorithm
.	O
</s>
<s>
They	O
are	O
relatively	O
rare	O
and	O
can	O
result	O
from	O
the	O
action	O
of	O
anti-arrhythmic	B-Algorithm
drugs	I-Algorithm
,	O
or	O
after	O
depolarizations	O
.	O
</s>
<s>
The	O
method	O
of	O
cardiac	B-Application
rhythm	I-Application
management	I-Application
depends	O
firstly	O
on	O
whether	O
the	O
affected	O
person	O
is	O
stable	O
or	O
unstable	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
people	O
admitted	O
to	O
the	O
hospital	O
with	O
cardiac	B-Application
arrhythmia	I-Application
and	O
conduction	B-Algorithm
disorders	I-Algorithm
with	O
and	O
without	O
complications	O
were	O
admitted	O
to	O
the	O
intensive	O
care	O
unit	O
more	O
than	O
half	O
the	O
time	O
in	O
2011	O
.	O
</s>
<s>
Several	O
physical	O
acts	O
can	O
increase	O
parasympathetic	O
nervous	O
supply	O
to	O
the	O
heart	O
,	O
resulting	O
in	O
blocking	O
of	O
electrical	O
conduction	B-Algorithm
through	O
the	O
AV	O
node	O
.	O
</s>
<s>
This	O
can	O
slow	O
down	O
or	O
stop	O
several	O
arrhythmias	B-Application
that	O
originate	O
above	O
or	O
at	O
the	O
AV	O
node	O
(	O
see	O
main	O
article	O
:	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
)	O
.	O
</s>
<s>
There	O
are	O
many	O
classes	O
of	O
antiarrhythmic	B-Algorithm
medications	I-Algorithm
,	O
with	O
different	O
mechanisms	O
of	O
action	O
and	O
many	O
different	O
individual	O
drugs	O
within	O
these	O
classes	O
.	O
</s>
<s>
Although	O
the	O
goal	O
of	O
drug	O
therapy	O
is	O
to	O
prevent	O
arrhythmia	B-Application
,	O
nearly	O
every	O
antiarrhythmic	B-Algorithm
drug	I-Algorithm
has	O
the	O
potential	O
to	O
act	O
as	O
a	O
pro-arrhythmic	O
,	O
and	O
so	O
must	O
be	O
carefully	O
selected	O
and	O
used	O
under	O
medical	O
supervision	O
.	O
</s>
<s>
Several	O
groups	O
of	O
drugs	O
slow	O
conduction	B-Algorithm
through	O
the	O
heart	O
,	O
without	O
actually	O
preventing	O
an	O
arrhythmia	B-Application
.	O
</s>
<s>
Some	O
arrhythmias	B-Application
promote	O
blood	O
clotting	O
within	O
the	O
heart	O
and	O
increase	O
the	O
risk	O
of	O
embolus	O
and	O
stroke	O
.	O
</s>
<s>
Arrhythmias	B-Application
may	O
also	O
be	O
treated	O
electrically	O
,	O
by	O
applying	O
a	O
shock	O
across	O
the	O
heart	O
–	O
either	O
externally	O
to	O
the	O
chest	O
wall	O
,	O
or	O
internally	O
to	O
the	O
heart	O
via	O
implanted	O
electrodes	O
.	O
</s>
<s>
It	O
is	O
used	O
for	O
the	O
treatment	O
of	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
.	O
</s>
<s>
It	O
is	O
needed	O
for	O
the	O
chaotic	O
rhythm	O
of	O
ventricular	O
fibrillation	O
and	O
is	O
also	O
used	O
for	O
pulseless	B-Application
ventricular	I-Application
tachycardia	I-Application
.	O
</s>
<s>
Electrical	O
treatment	O
of	O
arrhythmias	B-Application
also	O
includes	O
cardiac	B-Device
pacing	I-Device
.	O
</s>
<s>
Temporary	O
pacing	O
may	O
be	O
necessary	O
for	O
reversible	O
causes	O
of	O
very	O
slow	O
heartbeats	O
,	O
or	O
bradycardia	B-Algorithm
(	O
for	O
example	O
,	O
from	O
drug	O
overdose	O
or	O
myocardial	O
infarction	O
)	O
.	O
</s>
<s>
A	O
permanent	B-Device
pacemaker	I-Device
may	O
be	O
placed	O
in	O
situations	O
where	O
the	O
bradycardia	B-Algorithm
is	O
not	O
expected	O
to	O
recover	O
.	O
</s>
<s>
This	O
allows	O
abnormal	O
areas	O
of	O
conduction	B-Algorithm
to	O
be	O
located	O
very	O
accurately	O
and	O
subsequently	O
destroyed	O
by	O
heat	O
,	O
cold	O
,	O
electrical	O
,	O
or	O
laser	O
probes	O
in	O
a	O
process	O
called	O
catheter	O
ablation	O
.	O
</s>
<s>
This	O
procedure	O
may	O
be	O
completely	O
curative	O
for	O
some	O
forms	O
of	O
arrhythmia	B-Application
,	O
but	O
for	O
others	O
,	O
the	O
success	O
rate	O
remains	O
disappointing	O
.	O
</s>
<s>
AV	B-Algorithm
nodal	I-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
is	O
often	O
curable	O
by	O
ablating	O
one	O
of	O
the	O
pathways	O
in	O
the	O
AV	O
node	O
(	O
usually	O
the	O
slow	O
pathway	O
)	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
can	O
also	O
be	O
treated	O
,	O
by	O
performing	O
a	O
pulmonary	O
vein	O
isolation	O
,	O
but	O
the	O
results	O
are	O
less	O
reliable	O
.	O
</s>
<s>
Arrhythmias	B-Application
due	O
to	O
medications	O
have	O
been	O
reported	O
since	O
the	O
1920s	O
with	O
the	O
use	O
of	O
quinine	O
.	O
</s>
