<s>
Antiarrhythmic	B-Algorithm
agents	I-Algorithm
,	O
also	O
known	O
as	O
cardiac	B-Algorithm
dysrhythmia	I-Algorithm
medications	I-Algorithm
,	O
are	O
a	O
group	O
of	O
pharmaceuticals	O
that	O
are	O
used	O
to	O
suppress	O
abnormally	O
fast	O
rhythms	O
(	O
tachycardias	B-Application
)	O
,	O
such	O
as	O
atrial	B-Application
fibrillation	I-Application
,	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
and	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
Many	O
attempts	O
have	O
been	O
made	O
to	O
classify	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
.	O
</s>
<s>
Many	O
of	O
the	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
have	O
multiple	O
modes	O
of	O
action	O
,	O
which	O
makes	O
any	O
classification	O
imprecise	O
.	O
</s>
<s>
The	O
cardiac	O
myocyte	O
has	O
two	O
general	O
types	O
of	O
action	B-Algorithm
potentials	I-Algorithm
:	O
conduction	B-Algorithm
system	I-Algorithm
and	O
working	O
myocardium	O
.	O
</s>
<s>
The	O
action	B-Algorithm
potential	I-Algorithm
is	O
divided	O
into	O
5	O
phases	O
and	O
shown	O
in	O
the	O
diagram	O
.	O
</s>
<s>
The	O
five	O
main	O
classes	O
in	O
the	O
Vaughan	O
Williams	O
classification	O
of	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
are	O
:	O
</s>
<s>
With	O
regard	O
to	O
management	O
of	O
atrial	B-Application
fibrillation	I-Application
,	O
classes	O
I	O
and	O
III	O
are	O
used	O
in	O
rhythm	O
control	O
as	O
medical	O
cardioversion	O
agents	O
,	O
while	O
classes	O
II	O
and	O
IV	O
are	O
used	O
as	O
rate-control	O
agents	O
.	O
</s>
<s>
Diagnose	O
and	O
treat	O
Supraventricular	B-Algorithm
Tachycardias	I-Algorithm
(	O
Adenosine	O
)	O
Singh	O
,	O
S.	O
,	O
&	O
McKintosh	O
,	O
R	O
.	O
(	O
2022	O
,	O
September	O
10	O
)	O
.	O
</s>
<s>
The	O
class	O
I	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
interfere	O
with	O
the	O
sodium	O
channel	O
.	O
</s>
<s>
Class	O
I	O
agents	O
are	O
grouped	O
by	O
what	O
effect	O
they	O
have	O
on	O
the	O
Na+	O
channel	O
,	O
and	O
what	O
effect	O
they	O
have	O
on	O
cardiac	B-Algorithm
action	I-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
(	O
Also	O
noteworthy	O
is	O
that	O
a	O
few	O
class	O
II	O
agents	O
like	O
propranolol	O
also	O
have	O
a	O
membrane	B-Algorithm
stabilizing	I-Algorithm
effect	I-Algorithm
.	O
)	O
</s>
<s>
Class	O
I	O
agents	O
are	O
divided	O
into	O
three	O
groups	O
(	O
Ia	O
,	O
Ib	O
,	O
and	O
Ic	O
)	O
based	O
upon	O
their	O
effect	O
on	O
the	O
length	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
These	O
agents	O
are	O
particularly	O
useful	O
in	O
the	O
treatment	O
of	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
.	O
</s>
<s>
They	O
decrease	O
conduction	B-Algorithm
through	O
the	O
AV	O
node	O
.	O
</s>
<s>
Since	O
these	O
agents	O
do	O
not	O
affect	O
the	O
sodium	O
channel	O
,	O
conduction	B-Algorithm
velocity	O
is	O
not	O
decreased	O
.	O
</s>
<s>
The	O
prolongation	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
duration	O
and	O
refractory	O
period	O
,	O
combined	O
with	O
the	O
maintenance	O
of	O
normal	O
conduction	B-Algorithm
velocity	O
,	O
prevent	O
re-entrant	O
arrhythmias	B-Application
.	O
</s>
<s>
Class	O
III	O
agents	O
have	O
the	O
potential	O
to	O
prolong	O
the	O
QT	O
interval	O
of	O
the	O
EKG	B-Application
,	O
and	O
may	O
be	O
proarrhythmic	O
(	O
more	O
associated	O
with	O
development	O
of	O
polymorphic	O
VT	O
)	O
.	O
</s>
<s>
They	O
decrease	O
conduction	B-Algorithm
through	O
the	O
AV	O
node	O
,	O
and	O
shorten	O
phase	O
two	O
(	O
the	O
plateau	O
)	O
of	O
the	O
cardiac	B-Algorithm
action	I-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
Adenosine	O
is	O
used	O
intravenously	O
for	O
terminating	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
.	O
</s>
<s>
Digoxin	O
decreases	O
conduction	B-Algorithm
of	O
electrical	O
impulses	O
through	O
the	O
AV	O
node	O
and	O
increases	O
vagal	O
activity	O
via	O
its	O
action	O
on	O
the	O
central	O
nervous	O
system	O
.	O
</s>
<s>
Via	O
indirect	O
action	O
,	O
it	O
leads	O
to	O
an	O
increase	O
in	O
acetylcholine	O
production	O
,	O
stimulating	O
M2	O
receptors	O
on	O
AV	O
node	O
leading	O
to	O
an	O
overall	O
decrease	O
in	O
speed	O
of	O
conduction	B-Algorithm
.	O
</s>
<s>
Magnesium	O
sulfate	O
is	O
an	O
antiarrhythmic	B-Algorithm
drug	I-Algorithm
,	O
but	O
only	O
used	O
against	O
very	O
specific	O
arrhythmias	B-Application
such	O
as	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
.	O
</s>
<s>
Differing	O
from	O
other	O
authors	O
,	O
Vaughan-Williams	O
describe	O
the	O
main	O
action	O
as	O
a	O
slowing	O
of	O
the	O
rising	O
phase	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
Compounds	O
that	O
prolong	O
the	O
action	B-Algorithm
potential	I-Algorithm
:	O
matching	O
the	O
modern	O
classification	O
,	O
with	O
the	O
key	O
drug	O
example	O
being	O
amiodarone	O
,	O
and	O
a	O
surgical	O
example	O
being	O
thyroidectomy	O
.	O
</s>
<s>
The	O
result	O
is	O
an	O
expanded	O
but	O
pragmatic	O
classification	O
that	O
encompasses	O
approved	O
and	O
potential	O
anti-arrhythmic	B-Algorithm
drugs	I-Algorithm
.	O
</s>
<s>
This	O
will	O
aid	O
our	O
understanding	O
and	O
clinical	O
management	O
of	O
cardiac	B-Application
arrhythmias	I-Application
and	O
facilitate	O
future	O
therapeutic	O
developments	O
.	O
</s>
