<s>
Inappropriate	B-Algorithm
sinus	I-Algorithm
tachycardia	I-Algorithm
(	O
IST	O
)	O
is	O
a	O
rare	O
type	O
of	O
cardiac	B-Application
arrhythmia	I-Application
within	O
the	O
category	O
of	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
(	O
SVT	O
)	O
.	O
</s>
<s>
Research	O
into	O
the	O
mechanism	O
and	O
etiology	O
(	O
cause	O
)	O
of	O
inappropriate	B-Algorithm
sinus	I-Algorithm
tachycardia	I-Algorithm
is	O
ongoing	O
.	O
</s>
<s>
The	O
mechanism	O
and	O
primary	O
etiology	O
of	O
inappropriate	B-Algorithm
sinus	I-Algorithm
tachycardia	I-Algorithm
has	O
not	O
been	O
fully	O
elucidated	O
.	O
</s>
<s>
The	O
mechanism	O
of	O
the	O
arrhythmia	B-Application
primarily	O
involves	O
the	O
sinus	O
node	O
and	O
peri-nodal	O
tissue	O
and	O
does	O
not	O
require	O
the	O
AV	O
node	O
for	O
maintenance	O
.	O
</s>
<s>
A	O
diagnosis	O
of	O
inappropriate	B-Algorithm
sinus	I-Algorithm
tachycardia	I-Algorithm
is	O
primarily	O
one	O
of	O
exclusion	O
,	O
and	O
the	O
following	O
may	O
be	O
observed	O
:	O
</s>
<s>
Some	O
types	O
of	O
medication	O
tried	O
by	O
cardiologists	O
and	O
other	O
physicians	O
include	O
:	O
beta	O
blockers	O
,	O
selective	O
sinus	O
node	O
If	O
channel	O
inhibitors	O
(	O
such	O
as	O
ivabradine	O
)	O
,	O
calcium	O
channel	O
blockers	O
,	O
and	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
.	O
</s>
<s>
Some	O
SSRI	O
drugs	O
are	O
also	O
occasionally	O
tried	O
,	O
as	O
are	O
treatments	O
more	O
commonly	O
used	O
to	O
treat	O
postural	O
orthostatic	O
tachycardia	B-Application
syndrome	O
,	O
such	O
as	O
fludrocortisone	O
.	O
</s>
<s>
Invasive	O
treatments	O
include	O
forms	O
of	O
catheter	O
ablation	O
such	O
as	O
sinus	O
node	O
modification	O
(	O
selective	O
ablation	O
of	O
the	O
sinus	O
node	O
)	O
,	O
complete	O
sinus	O
node	O
ablation	O
(	O
with	O
associated	O
implantation	O
of	O
a	O
permanent	O
artificial	B-Device
pacemaker	I-Device
)	O
,	O
and	O
AV	O
node	O
ablation	O
in	O
very	O
resistant	O
cases	O
(	O
creation	O
of	O
iatrogenic	O
complete	B-Architecture
heart	I-Architecture
block	I-Architecture
,	O
necessitating	O
implantation	O
of	O
a	O
permanent	O
artificial	B-Device
pacemaker	I-Device
)	O
.	O
</s>
<s>
Upon	O
exertion	O
,	O
an	O
inappropriate	O
heart	O
rate	O
response	O
of	O
sinus	B-Algorithm
tachycardia	I-Algorithm
can	O
be	O
seen	O
in	O
some	O
Inborn	O
Errors	O
of	O
Metabolism	O
that	O
result	O
in	O
metabolic	O
myopathies	O
,	O
such	O
as	O
McArdle	O
Disease	O
(	O
GSD-V	O
)	O
.	O
</s>
