<s>
Tachycardia	B-Application
,	O
also	O
called	O
tachyarrhythmia	B-Application
,	O
is	O
a	O
heart	O
rate	O
that	O
exceeds	O
the	O
normal	O
resting	O
rate	O
.	O
</s>
<s>
In	O
general	O
,	O
a	O
resting	O
heart	O
rate	O
over	O
100	O
beats	O
per	O
minute	O
is	O
accepted	O
as	O
tachycardia	B-Application
in	O
adults	O
.	O
</s>
<s>
Tachycardia	B-Application
can	O
lead	O
to	O
fainting	O
.	O
</s>
<s>
Some	O
causes	O
of	O
tachycardia	B-Application
include	O
:	O
</s>
<s>
Cutoff	O
values	O
for	O
tachycardia	B-Application
in	O
different	O
age	O
groups	O
are	O
fairly	O
well	O
standardized	O
;	O
typical	O
cutoffs	O
are	O
listed	O
below	O
:	O
</s>
<s>
The	O
increased	B-Application
heart	I-Application
rate	I-Application
also	O
leads	O
to	O
increased	O
work	O
and	O
oxygen	O
demand	O
by	O
the	O
heart	O
,	O
which	O
can	O
lead	O
to	O
rate	O
related	O
ischemia	O
.	O
</s>
<s>
An	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
is	O
used	O
to	O
classify	O
the	O
type	O
of	O
tachycardia	B-Application
.	O
</s>
<s>
They	O
may	O
be	O
classified	O
into	O
narrow	O
and	O
wide	O
complex	O
based	O
on	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
A	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardia	I-Algorithm
with	O
an	O
accessory	B-Algorithm
conduction	I-Algorithm
pathway	I-Algorithm
,	O
often	O
termed	O
"	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
with	O
pre-excitation	O
"	O
(	O
e.g.	O
</s>
<s>
Tachycardias	B-Application
may	O
be	O
classified	O
as	O
either	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardias	I-Algorithm
(	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
)	O
or	O
wide	B-Application
complex	I-Application
tachycardias	I-Application
.	O
</s>
<s>
Narrow	O
and	O
wide	O
refer	O
to	O
the	O
width	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Narrow	B-Algorithm
complex	I-Algorithm
tachycardias	I-Algorithm
tend	O
to	O
originate	O
in	O
the	O
atria	O
,	O
while	O
wide	B-Application
complex	I-Application
tachycardias	I-Application
tend	O
to	O
originate	O
in	O
the	O
ventricles	O
.	O
</s>
<s>
Tachycardias	B-Application
can	O
be	O
further	O
classified	O
as	O
either	O
regular	O
or	O
irregular	O
.	O
</s>
<s>
This	O
is	O
called	O
reflex	B-Algorithm
tachycardia	B-Application
.	O
</s>
<s>
Fever	O
,	O
hyperventilation	O
,	O
diarrhea	O
and	O
severe	O
infections	O
can	O
also	O
cause	O
tachycardia	B-Application
,	O
primarily	O
due	O
to	O
increase	O
in	O
metabolic	O
demands	O
.	O
</s>
<s>
Upon	O
exertion	O
,	O
sinus	B-Algorithm
tachycardia	I-Algorithm
can	O
also	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
's	O
disease	O
(	O
GSD-V	O
)	O
.	O
</s>
<s>
This	O
energy	O
shortage	O
in	O
muscle	O
cells	O
causes	O
an	O
inappropriate	O
rapid	B-Application
heart	I-Application
rate	I-Application
in	O
response	O
to	O
exercise	O
.	O
</s>
<s>
As	O
skeletal	O
muscle	O
relies	O
predominantly	O
on	O
glycogenolysis	O
for	O
the	O
first	O
few	O
minutes	O
as	O
it	O
transitions	O
from	O
rest	O
to	O
activity	O
,	O
as	O
well	O
as	O
throughout	O
high-intensity	O
aerobic	O
activity	O
and	O
all	O
anaerobic	O
activity	O
,	O
individuals	O
with	O
GSD-V	O
experience	O
during	O
exercise	O
:	O
sinus	B-Algorithm
tachycardia	I-Algorithm
,	O
tachypnea	O
,	O
muscle	O
fatigue	O
and	O
pain	O
,	O
during	O
the	O
aforementioned	O
activities	O
and	O
time	O
frames	O
.	O
</s>
<s>
This	O
is	O
the	O
basis	O
for	O
the	O
so-called	O
fight-or-flight	O
response	O
,	O
but	O
such	O
stimulation	O
can	O
also	O
be	O
induced	O
by	O
stimulants	O
such	O
as	O
ephedrine	O
,	O
amphetamines	O
or	O
cocaine	B-Application
.	O
</s>
<s>
Certain	O
endocrine	O
disorders	O
such	O
as	O
pheochromocytoma	O
can	O
also	O
cause	O
epinephrine	O
release	O
and	O
can	O
result	O
in	O
tachycardia	B-Application
independent	O
of	O
nervous	O
system	O
stimulation	O
.	O
</s>
<s>
Hyperthyroidism	O
can	O
also	O
cause	O
tachycardia	B-Application
.	O
</s>
<s>
The	O
upper	O
limit	O
of	O
normal	O
rate	O
for	O
sinus	B-Algorithm
tachycardia	I-Algorithm
is	O
thought	O
to	O
be	O
220bpm	O
minus	O
age	O
.	O
</s>
<s>
Inappropriate	B-Algorithm
sinus	I-Algorithm
tachycardia	I-Algorithm
(	O
IST	O
)	O
is	O
a	O
rare	O
but	O
benign	O
type	O
of	O
cardiac	B-Application
arrhythmia	I-Application
that	O
may	O
be	O
caused	O
by	O
a	O
structural	O
abnormality	O
in	O
the	O
sinus	O
node	O
.	O
</s>
<s>
Ventricular	B-Application
tachycardia	I-Application
(	O
VT	O
or	O
V-tach	B-Application
)	O
is	O
a	O
potentially	O
life-threatening	O
cardiac	B-Application
arrhythmia	I-Application
that	O
originates	O
in	O
the	O
ventricles	O
.	O
</s>
<s>
It	O
is	O
usually	O
a	O
regular	O
,	O
wide	B-Application
complex	I-Application
tachycardia	I-Application
with	O
a	O
rate	O
between	O
120	O
and	O
250	O
beats	O
per	O
minute	O
.	O
</s>
<s>
A	O
medically	O
significant	O
subvariant	O
of	O
ventricular	B-Application
tachycardia	I-Application
is	O
called	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
(	O
literally	O
meaning	O
"	O
twisting	O
of	O
the	O
points	O
"	O
,	O
due	O
to	O
its	O
appearance	O
on	O
an	O
EKG	B-Application
)	O
,	O
which	O
tends	O
to	O
result	O
from	O
a	O
long	O
QT	O
interval	O
.	O
</s>
<s>
Both	O
of	O
these	O
rhythms	O
normally	O
last	O
for	O
only	O
a	O
few	O
seconds	O
to	O
minutes	O
(	O
paroxysmal	O
tachycardia	B-Application
)	O
,	O
but	O
if	O
VT	O
persists	O
it	O
is	O
extremely	O
dangerous	O
,	O
often	O
leading	O
to	O
ventricular	O
fibrillation	O
.	O
</s>
<s>
This	O
is	O
a	O
type	O
of	O
tachycardia	B-Application
that	O
originates	O
from	O
above	O
the	O
ventricles	O
,	O
such	O
as	O
the	O
atria	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
known	O
as	O
paroxysmal	B-Algorithm
atrial	I-Algorithm
tachycardia	I-Algorithm
(	O
PAT	O
)	O
.	O
</s>
<s>
Several	O
types	O
of	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
are	O
known	O
to	O
exist	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
is	O
one	O
of	O
the	O
most	O
common	O
cardiac	B-Application
arrhythmias	I-Application
.	O
</s>
<s>
However	O
,	O
it	O
may	O
show	O
wide	O
QRS	B-Algorithm
complexes	I-Algorithm
on	O
the	O
ECG	B-Application
if	O
a	O
bundle	B-Algorithm
branch	I-Algorithm
block	I-Algorithm
is	O
present	O
.	O
</s>
<s>
At	O
high	O
rates	O
,	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
may	O
also	O
become	O
wide	O
due	O
to	O
the	O
Ashman	B-Algorithm
phenomenon	I-Algorithm
.	O
</s>
<s>
Depending	O
on	O
the	O
patient	O
's	O
health	O
and	O
other	O
variables	O
such	O
as	O
medications	O
taken	O
for	O
rate	O
control	O
,	O
atrial	B-Application
fibrillation	I-Application
may	O
cause	O
heart	O
rates	O
that	O
span	O
from	O
50	O
to	O
250	O
beats	O
per	O
minute	O
(	O
or	O
even	O
higher	O
if	O
an	O
accessory	B-Algorithm
pathway	I-Algorithm
is	O
present	O
)	O
.	O
</s>
<s>
However	O
,	O
new-onset	O
atrial	B-Application
fibrillation	I-Application
tends	O
to	O
present	O
with	O
rates	O
between	O
100	O
and	O
150	O
beats	O
per	O
minute	O
.	O
</s>
<s>
AV	B-Algorithm
nodal	I-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
(	O
AVNRT	B-Algorithm
)	O
is	O
the	O
most	O
common	O
reentrant	O
tachycardia	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
regular	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardia	I-Algorithm
that	O
usually	O
responds	O
well	O
to	O
the	O
Valsalva	O
maneuver	O
or	O
the	O
drug	O
adenosine	O
.	O
</s>
<s>
AV	B-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
(	O
AVRT	B-Algorithm
)	O
requires	O
an	O
accessory	B-Algorithm
pathway	I-Algorithm
for	O
its	O
maintenance	O
.	O
</s>
<s>
AVRT	B-Algorithm
may	O
involve	O
orthodromic	O
conduction	O
(	O
where	O
the	O
impulse	O
travels	O
down	O
the	O
AV	O
node	O
to	O
the	O
ventricles	O
and	O
back	O
up	O
to	O
the	O
atria	O
through	O
the	O
accessory	B-Algorithm
pathway	I-Algorithm
)	O
or	O
antidromic	O
conduction	O
(	O
which	O
the	O
impulse	O
travels	O
down	O
the	O
accessory	B-Algorithm
pathway	I-Algorithm
and	O
back	O
up	O
to	O
the	O
atria	O
through	O
the	O
AV	O
node	O
)	O
.	O
</s>
<s>
Orthodromic	O
conduction	O
usually	O
results	O
in	O
a	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardia	I-Algorithm
,	O
and	O
antidromic	O
conduction	O
usually	O
results	O
in	O
a	O
wide	B-Application
complex	I-Application
tachycardia	I-Application
that	O
often	O
mimics	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
Most	O
antiarrhythmics	B-Algorithm
are	O
contraindicated	O
in	O
the	O
emergency	O
treatment	O
of	O
AVRT	B-Algorithm
,	O
because	O
they	O
may	O
paradoxically	O
increase	O
conduction	O
across	O
the	O
accessory	B-Algorithm
pathway	I-Algorithm
.	O
</s>
<s>
Junctional	B-Algorithm
tachycardia	I-Algorithm
is	O
an	O
automatic	B-Algorithm
tachycardia	I-Algorithm
originating	O
in	O
the	O
AV	O
junction	O
.	O
</s>
<s>
It	O
tends	O
to	O
be	O
a	O
regular	O
,	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardia	I-Algorithm
and	O
may	O
be	O
a	O
sign	O
of	O
digitalis	O
toxicity	O
.	O
</s>
<s>
The	O
management	O
of	O
tachycardia	B-Application
depends	O
on	O
its	O
type	O
(	O
wide	O
complex	O
versus	O
narrow	O
complex	O
)	O
,	O
whether	O
or	O
not	O
the	O
person	O
is	O
stable	O
or	O
unstable	O
,	O
and	O
whether	O
the	O
instability	O
is	O
due	O
to	O
the	O
tachycardia	B-Application
.	O
</s>
<s>
In	O
those	O
that	O
are	O
unstable	O
with	O
a	O
narrow	B-Algorithm
complex	I-Algorithm
tachycardia	I-Algorithm
,	O
intravenous	O
adenosine	O
may	O
be	O
attempted	O
.	O
</s>
<s>
Some	O
of	O
the	O
most	O
severe	O
and	O
unstable	O
forms	O
of	O
tachycardia	B-Application
have	O
been	O
known	O
to	O
manifest	O
during	O
long	O
sessions	O
of	O
sedentary	O
activities	O
,	O
such	O
as	O
playing	O
video	O
games	O
.	O
</s>
<s>
The	O
word	O
tachycardia	B-Application
came	O
to	O
English	O
from	O
New	O
Latin	O
as	O
a	O
neoclassical	O
compound	O
built	O
from	O
the	O
combining	O
forms	O
tachy	B-Application
-	O
+	O
-cardia	O
,	O
which	O
are	O
from	O
the	O
Greek	O
ταχύς	O
tachys	O
,	O
"	O
quick	O
,	O
rapid	O
"	O
and	O
καρδία	O
,	O
kardia	O
,	O
"	O
heart	O
"	O
.	O
</s>
<s>
As	O
a	O
matter	O
both	O
of	O
usage	O
choices	O
in	O
the	O
medical	O
literature	O
and	O
of	O
idiom	O
in	O
natural	O
language	O
,	O
the	O
words	O
tachycardia	B-Application
and	O
tachyarrhythmia	B-Application
are	O
usually	O
used	O
interchangeably	O
,	O
or	O
loosely	O
enough	O
that	O
precise	O
differentiation	O
is	O
not	O
explicit	O
.	O
</s>
<s>
The	O
distinction	O
is	O
that	O
tachycardia	B-Application
be	O
reserved	O
for	O
the	O
rapid	B-Application
heart	I-Application
rate	I-Application
itself	O
,	O
regardless	O
of	O
cause	O
,	O
physiologic	O
or	O
pathologic	O
(	O
that	O
is	O
,	O
from	O
healthy	O
response	O
to	O
exercise	O
or	O
from	O
cardiac	B-Application
arrhythmia	I-Application
)	O
,	O
and	O
that	O
tachyarrhythmia	B-Application
be	O
reserved	O
for	O
the	O
pathologic	O
form	O
(	O
that	O
is	O
,	O
an	O
arrhythmia	B-Application
of	O
the	O
rapid	O
rate	O
type	O
)	O
.	O
</s>
<s>
But	O
the	O
prescription	O
will	O
probably	O
never	O
be	O
successfully	O
imposed	O
on	O
general	O
usage	O
,	O
not	O
only	O
because	O
much	O
of	O
the	O
existing	O
medical	O
literature	O
ignores	O
it	O
even	O
when	O
the	O
words	O
stand	O
alone	O
but	O
also	O
because	O
the	O
terms	O
for	O
specific	O
types	O
of	O
arrhythmia	B-Application
(	O
standard	O
collocations	O
of	O
adjectives	O
and	O
noun	O
)	O
are	O
deeply	O
established	O
idiomatically	O
with	O
the	O
tachycardia	B-Application
version	O
as	O
the	O
more	O
commonly	O
used	O
version	O
.	O
</s>
<s>
Thus	O
SVT	O
is	O
called	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
more	O
than	O
twice	O
as	O
often	O
as	O
it	O
is	O
called	O
supraventricular	O
tachyarrhythmia	B-Application
;	O
moreover	O
,	O
those	O
two	O
terms	O
are	O
always	O
completely	O
synonymous	O
—	O
in	O
natural	O
language	O
there	O
is	O
no	O
such	O
term	O
as	O
"	O
healthy/physiologic	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
"	O
.	O
</s>
<s>
The	O
same	O
themes	O
are	O
also	O
true	O
of	O
AVRT	B-Algorithm
and	O
AVNRT	B-Algorithm
.	O
</s>
<s>
But	O
the	O
power	O
to	O
differentiate	O
in	O
an	O
idiomatic	O
way	O
is	O
not	O
lost	O
,	O
regardless	O
,	O
because	O
when	O
the	O
specification	O
of	O
physiologic	O
tachycardia	B-Application
is	O
needed	O
,	O
that	O
phrase	O
aptly	O
conveys	O
it	O
.	O
</s>
