<s>
It	O
is	O
an	O
electrical	O
disturbance	O
which	O
can	O
be	O
seen	O
on	O
an	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
.	O
</s>
<s>
Excessive	O
QT	O
prolongation	O
can	O
trigger	O
tachycardias	B-Application
such	O
as	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
(	O
TdP	O
)	O
.	O
</s>
<s>
QT	O
prolongation	O
is	O
an	O
established	O
side	O
effect	O
of	O
antiarrhythmics	B-Algorithm
,	O
but	O
can	O
also	O
be	O
caused	O
by	O
a	O
wide	O
range	O
of	O
non-cardiac	O
medicines	O
,	O
including	O
antibiotics	O
,	O
antihistamines	O
,	O
opioids	O
,	O
and	O
complementary	O
medicines	O
.	O
</s>
<s>
On	O
an	O
ECG	B-Application
,	O
the	O
QT	B-Algorithm
interval	I-Algorithm
represents	O
the	O
summation	O
of	O
action	B-Algorithm
potentials	I-Algorithm
in	O
cardiac	O
muscle	O
cells	O
,	O
which	O
can	O
be	O
caused	O
by	O
an	O
increase	O
in	O
inward	O
current	O
through	O
sodium	O
or	O
calcium	O
channels	O
,	O
or	O
a	O
decrease	O
in	O
outward	O
current	O
through	O
potassium	O
channels	O
.	O
</s>
<s>
A	O
QT	B-Algorithm
interval	I-Algorithm
is	O
a	O
value	O
that	O
is	O
measured	O
on	O
an	O
electrocardiogram	B-Application
.	O
</s>
<s>
The	O
value	O
for	O
a	O
normal	O
QT	B-Algorithm
interval	I-Algorithm
is	O
similar	O
in	O
males	O
and	O
females	O
from	O
birth	O
up	O
to	O
adolescence	O
.	O
</s>
<s>
During	O
infancy	O
,	O
a	O
normal	O
QTc	B-Algorithm
is	O
defined	O
as	O
400	O
+	O
/	O
-	O
20	O
milliseconds	O
.	O
</s>
<s>
Before	O
puberty	O
,	O
the	O
99th	O
percentile	O
of	O
QTc	B-Algorithm
values	O
is	O
460	O
milliseconds	O
.	O
</s>
<s>
Torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
(	O
TdP	O
)	O
is	O
an	O
arrhythmia	O
.	O
</s>
<s>
More	O
specifically	O
,	O
it	O
is	O
one	O
form	O
of	O
a	O
polymorphic	B-Application
ventricular	I-Application
tachycardia	I-Application
that	O
presents	O
with	O
a	O
long	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
Diagnosis	O
is	O
made	O
by	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
,	O
which	O
shows	O
rapid	O
irregular	O
QRS	O
complexes	O
.	O
</s>
<s>
The	O
term	O
"	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
"	O
is	O
translated	O
from	O
French	O
as	O
"	O
twisting	O
of	O
the	O
peaks	O
"	O
because	O
the	O
complexes	O
appear	O
to	O
undulate	O
,	O
or	O
twist	O
around	O
,	O
the	O
EKG	B-Application
baseline	O
.	O
</s>
<s>
In	O
addition	O
,	O
factors	O
such	O
as	O
rapid	O
infusion	O
,	O
concurrent	O
use	O
of	O
more	O
than	O
one	O
drug	O
known	O
to	O
prolong	O
QT	B-Algorithm
interval	I-Algorithm
,	O
diuretic	O
treatment	O
,	O
electrolyte	O
derangements	O
(	O
hypokalemia	O
,	O
hypomagnesemia	O
,	O
or	O
hypocalcemia	O
)	O
,	O
advanced	O
age	O
,	O
bradyarrhythmias	B-Algorithm
,	O
and	O
female	O
sex	O
have	O
all	O
been	O
shown	O
to	O
be	O
risk	O
factors	O
for	O
developing	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
.	O
</s>
<s>
The	O
QTc	B-Algorithm
interval	O
is	O
longer	O
in	O
females	O
,	O
as	O
well	O
as	O
having	O
a	O
stronger	O
response	O
to	O
IKr-blocking	O
agents	O
.	O
</s>
<s>
In	O
males	O
,	O
the	O
presence	O
of	O
testosterone	O
upregulates	O
IKr	O
channels	O
and	O
therefore	O
decreases	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
Stated	O
otherwise	O
,	O
estrogens	O
prolong	O
the	O
QT	B-Algorithm
interval	I-Algorithm
,	O
while	O
androgens	O
shorten	O
it	O
and	O
decrease	O
the	O
response	O
to	O
IKr-blocking	O
agents	O
.	O
</s>
<s>
The	O
main	O
groups	O
of	O
drugs	O
that	O
can	O
cause	O
QT	O
prolongation	O
are	O
antiarrythmic	B-Algorithm
medications	I-Algorithm
,	O
psychiatric	O
medications	O
,	O
and	O
antibiotics	O
.	O
</s>
<s>
Blocking	O
sodium	O
channels	O
tend	O
to	O
shorten	O
the	O
action	B-Algorithm
potential	I-Algorithm
duration	O
,	O
while	O
blocking	O
potassium	O
channels	O
prolongs	O
the	O
action	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
Class	O
III	O
antiarrhythmic	B-Algorithm
drugs	I-Algorithm
are	O
potassium	O
channel	O
blockers	O
that	O
cause	O
QT	O
prolongation	O
and	O
are	O
associated	O
with	O
TdP	O
.	O
</s>
<s>
Ibutilide	O
differs	O
from	O
other	O
class	O
III	O
antiarrhythmic	B-Algorithm
agents	I-Algorithm
in	O
that	O
it	O
activates	O
the	O
slow	O
,	O
delayed	O
inward	O
sodium	O
channels	O
rather	O
than	O
inhibiting	O
outward	O
potassium	O
channels	O
.	O
</s>
<s>
Psychiatric	O
medications	O
include	O
antipsychotics	O
and	O
antidepressants	O
that	O
have	O
been	O
shown	O
to	O
lengthen	O
the	O
QT	B-Algorithm
interval	I-Algorithm
and	O
induce	O
TdP	O
,	O
especially	O
when	O
given	O
intravenously	O
or	O
in	O
higher	O
concentrations	O
.	O
</s>
<s>
Patients	O
taking	O
haloperidol	O
are	O
at	O
a	O
higher	O
risk	O
if	O
they	O
also	O
have	O
electrolyte	O
abnormalities	O
(	O
such	O
as	O
hypokalemia	O
and/or	O
hypomagnesemia	O
)	O
,	O
congenital	O
LQTS	O
,	O
cardiac	O
abnormalities	O
,	O
hypothyroidism	O
,	O
or	O
if	O
they	O
are	O
concurrently	O
taking	O
other	O
medications	O
known	O
to	O
lengthen	O
the	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
An	O
ECG	B-Application
is	O
recommended	O
before	O
patients	O
are	O
prescribed	O
SSRI	O
agents	O
citalopram	O
and	O
escitalopram	O
if	O
the	O
prescribed	O
dose	O
is	O
above	O
40	O
mg	O
or	O
20	O
mg	O
per	O
day	O
,	O
respectively	O
.	O
</s>
<s>
On	O
EKG	B-Application
,	O
the	O
QT	B-Algorithm
interval	I-Algorithm
represents	O
the	O
summation	O
of	O
action	B-Algorithm
potentials	I-Algorithm
in	O
cardiac	O
muscle	O
cells	O
.	O
</s>
<s>
QT	O
prolongation	O
therefore	O
results	O
from	O
action	B-Algorithm
potential	I-Algorithm
prolongation	O
,	O
which	O
can	O
be	O
caused	O
by	O
an	O
increase	O
in	O
inward	O
current	O
through	O
sodium	O
or	O
calcium	O
channels	O
,	O
or	O
a	O
decrease	O
in	O
outward	O
current	O
through	O
potassium	O
channels	O
.	O
</s>
<s>
Most	O
patients	O
with	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
are	O
asymptomatic	O
and	O
are	O
diagnosed	O
solely	O
by	O
EKG	B-Application
in	O
association	O
with	O
a	O
history	O
of	O
using	O
medications	O
known	O
to	O
cause	O
QT	O
prolongation	O
.	O
</s>
<s>
An	O
EKG	B-Application
should	O
be	O
obtained	O
,	O
a	O
cardiac	O
monitor	O
should	O
be	O
attached	O
,	O
IV	O
access	O
should	O
be	O
established	O
,	O
supplemental	O
oxygen	O
should	O
be	O
given	O
,	O
and	O
blood	O
samples	O
should	O
be	O
sent	O
for	O
appropriate	O
studies	O
.	O
</s>
<s>
Unstable	O
patients	O
exhibit	O
signs	O
of	O
chest	O
pain	O
,	O
hypotension	O
,	O
elevated	B-Application
heart	I-Application
rate	I-Application
,	O
and/or	O
heart	O
failure	O
.	O
</s>
<s>
Patients	O
with	O
cardiac	O
arrest	O
should	O
be	O
given	O
IV	O
magnesium	O
sulfate	O
over	O
a	O
period	O
of	O
two	O
minutes.After	O
diagnosing	O
and	O
treating	O
the	O
cause	O
of	O
LQTS	O
,	O
it	O
is	O
also	O
important	O
to	O
perform	O
a	O
thorough	O
history	O
and	O
EKG	B-Application
screening	O
.	O
</s>
<s>
Unfortunately	O
,	O
there	O
is	O
no	O
absolute	O
definition	O
that	O
describes	O
the	O
incidence	O
of	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
,	O
as	O
most	O
data	O
is	O
obtained	O
from	O
case	O
reports	O
or	O
small	O
observational	O
studies	O
.	O
</s>
<s>
Although	O
QT	B-Algorithm
interval	I-Algorithm
prolongation	O
is	O
one	O
of	O
the	O
most	O
common	O
reasons	O
for	O
drug	O
withdrawal	O
from	O
the	O
market	O
,	O
the	O
overall	O
incidence	O
of	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
is	O
difficult	O
to	O
estimate	O
.	O
</s>
<s>
One	O
study	O
in	O
France	O
estimated	O
that	O
between	O
5-7	O
%	O
of	O
reports	O
of	O
ventricular	B-Application
tachycardia	I-Application
,	O
ventricular	O
fibrillation	O
,	O
or	O
sudden	O
cardiac	O
death	O
were	O
in	O
fact	O
due	O
to	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
and	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
.	O
</s>
<s>
An	O
observational	O
study	O
from	O
the	O
Netherlands	O
showed	O
that	O
3.1	O
%	O
of	O
patients	O
who	O
experienced	O
sudden	O
cardiac	O
death	O
were	O
also	O
using	O
a	O
QT-prolonging	B-Algorithm
drug	I-Algorithm
.	O
</s>
