<s>
Torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
,	O
torsade	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
or	O
torsades	B-Algorithm
des	I-Algorithm
pointes	I-Algorithm
(	O
TdP	O
)	O
(	O
,	O
,	O
translated	O
as	O
"	O
twisting	O
of	O
peaks	O
"	O
)	O
is	O
a	O
specific	O
type	O
of	O
abnormal	B-Application
heart	I-Application
rhythm	I-Application
that	O
can	O
lead	O
to	O
sudden	O
cardiac	O
death	O
.	O
</s>
<s>
It	O
is	O
a	O
polymorphic	B-Application
ventricular	I-Application
tachycardia	I-Application
that	O
exhibits	O
distinct	O
characteristics	O
on	O
the	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
.	O
</s>
<s>
Prolongation	O
of	O
the	O
QT	B-Algorithm
interval	I-Algorithm
can	O
increase	O
a	O
person	O
's	O
risk	O
of	O
developing	O
this	O
abnormal	B-Application
heart	I-Application
rhythm	I-Application
,	O
occurring	O
in	O
between	O
1%	O
and	O
10%	O
of	O
patients	O
who	O
receive	O
QT-prolonging	O
antiarrhythmic	O
drugs	O
.	O
</s>
<s>
Symptoms	O
and	O
consequences	O
include	O
palpitations	B-Algorithm
,	O
dizziness	O
,	O
lightheadedness	O
(	O
during	O
shorter	O
episodes	O
)	O
,	O
fainting	O
(	O
during	O
longer	O
episodes	O
)	O
,	O
and	O
sudden	O
cardiac	O
death	O
.	O
</s>
<s>
Torsades	B-Algorithm
occurs	O
as	O
both	O
an	O
inherited	O
(	O
linked	O
to	O
at	O
least	O
17	O
genes	O
)	O
and	O
as	O
an	O
acquired	O
form	O
caused	O
most	O
often	O
by	O
drugs	O
and/or	O
electrolyte	O
disorders	O
that	O
cause	O
excessive	O
lengthening	O
of	O
the	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
Common	O
causes	O
for	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
include	O
drug-induced	B-Algorithm
QT	I-Algorithm
prolongation	I-Algorithm
and	O
less	O
often	O
diarrhea	O
,	O
low	O
serum	O
magnesium	O
,	O
and	O
low	O
serum	O
potassium	O
or	O
congenital	O
long	O
QT	O
syndrome	O
.	O
</s>
<s>
Certain	O
drugs	O
and	O
combinations	O
of	O
drugs	O
resulting	O
in	O
drug	O
interactions	O
are	O
common	O
contributors	O
to	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
risk	O
.	O
</s>
<s>
QT-prolonging	O
medications	O
such	O
as	O
clarithromycin	O
,	O
levofloxacin	O
,	O
or	O
haloperidol	O
,	O
when	O
taken	O
concurrently	O
with	O
cytochrome	O
P450	O
inhibitors	O
,	O
such	O
as	O
fluoxetine	O
,	O
cimetidine	O
,	O
or	O
particular	O
foods	O
including	O
grapefruit	O
,	O
can	O
result	O
in	O
higher-than-normal	O
levels	O
of	O
medications	B-Algorithm
that	I-Algorithm
prolong	I-Algorithm
the	I-Algorithm
QT	I-Algorithm
interval	I-Algorithm
in	O
the	O
bloodstream	O
and	O
therefore	O
increase	O
a	O
person	O
's	O
risk	O
of	O
developing	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
.	O
</s>
<s>
In	O
one	O
example	O
,	O
the	O
gastrokinetic	O
drug	O
cisapride	O
(	O
Propulsid	O
)	O
was	O
withdrawn	O
from	O
the	O
US	O
market	O
in	O
2000	O
after	O
it	O
was	O
linked	O
to	O
deaths	O
caused	O
by	O
long	O
QT	O
syndrome-induced	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
.	O
</s>
<s>
The	O
following	O
is	O
a	O
partial	O
list	O
of	O
factors	O
associated	O
with	O
an	O
increased	O
tendency	O
towards	O
developing	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
:	O
</s>
<s>
In	O
Torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
,	O
however	O
,	O
the	O
repolarization	O
is	O
prolonged	O
;	O
this	O
can	O
be	O
due	O
to	O
electrolyte	O
disturbances	O
(	O
hypokalemia	O
,	O
hypomagnesemia	O
,	O
hypocalcemia	O
)	O
,	O
bradycardia	B-Algorithm
,	O
certain	O
drugs	O
(	O
disopyramide	O
,	O
sotalol	O
,	O
amiodarone	O
,	O
amitriptyline	O
,	O
chlorpromazine	O
,	O
erythromycin	O
)	O
and/or	O
congenital	O
syndromes	O
.	O
</s>
<s>
The	O
ECG	B-Application
tracing	O
in	O
torsades	B-Algorithm
demonstrates	O
a	O
polymorphic	B-Application
ventricular	I-Application
tachycardia	I-Application
with	O
a	O
characteristic	O
illusion	O
of	O
a	O
twisting	O
of	O
the	O
QRS	O
complex	O
around	O
the	O
isoelectric	O
baseline	O
(	O
peaks	O
,	O
which	O
are	O
at	O
first	O
pointing	O
up	O
,	O
appear	O
to	O
be	O
pointing	O
down	O
for	O
subsequent	O
"	O
beats	O
"	O
when	O
looking	O
at	O
ECG	B-Application
traces	O
of	O
the	O
"	O
heartbeat	O
"	O
)	O
.	O
</s>
<s>
Depending	O
on	O
their	O
cause	O
,	O
most	O
individual	O
episodes	O
of	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
revert	O
to	O
normal	O
sinus	O
rhythm	O
within	O
a	O
few	O
seconds	O
;	O
however	O
,	O
episodes	O
may	O
also	O
persist	O
and	O
possibly	O
degenerate	O
into	O
ventricular	O
fibrillation	O
,	O
leading	O
to	O
sudden	O
death	O
in	O
the	O
absence	O
of	O
prompt	O
medical	O
intervention	O
.	O
</s>
<s>
Torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
is	O
associated	O
with	O
long	O
QT	O
syndrome	O
,	O
a	O
condition	O
whereby	O
prolonged	O
QT	B-Algorithm
intervals	I-Algorithm
are	O
visible	O
on	O
an	O
ECG	B-Application
.	O
</s>
<s>
Long	O
QT	B-Algorithm
intervals	I-Algorithm
predispose	O
the	O
patient	O
to	O
an	O
,	O
wherein	O
the	O
R-wave	O
,	O
representing	O
ventricular	B-Application
depolarization	I-Application
,	O
occurs	O
during	O
the	O
relative	O
refractory	O
period	O
at	O
the	O
end	O
of	O
repolarization	O
(	O
represented	O
by	O
the	O
latter	O
half	O
of	O
the	O
T-wave	B-Algorithm
)	O
.	O
</s>
<s>
An	O
R-on-T	O
can	O
initiate	O
torsades	B-Algorithm
.	O
</s>
<s>
Sometimes	O
,	O
pathologic	O
T-U	O
waves	O
may	O
be	O
seen	O
in	O
the	O
ECG	B-Application
before	O
the	O
initiation	O
of	O
torsades	B-Algorithm
.	O
</s>
<s>
A	O
"	O
short-coupled	O
variant	O
of	O
torsade	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
"	O
,	O
which	O
presents	O
without	O
long	O
QT	O
syndrome	O
,	O
was	O
also	O
described	O
in	O
1994	O
as	O
having	O
the	O
following	O
characteristics	O
:	O
</s>
<s>
The	O
R-on-T	O
phenomenon	O
is	O
the	O
superimposition	O
of	O
a	O
premature	B-Error_Name
ventricular	I-Error_Name
contraction	I-Error_Name
on	O
the	O
T	B-Algorithm
wave	I-Algorithm
of	O
a	O
preceding	O
heart	O
beat	O
.	O
</s>
<s>
Studies	O
suggest	O
that	O
R-on-T	O
phenomenon	O
is	O
likely	O
to	O
start	O
a	O
sustained	B-Application
ventricular	I-Application
tachycardia	I-Application
and	O
ventricular	O
fibrillation	O
.	O
</s>
<s>
It	O
's	O
considered	O
a	O
cardiac	B-Application
arrhythmia	I-Application
in	O
which	O
the	O
ventricles	O
of	O
the	O
heart	O
become	O
again	O
excited	O
during	O
the	O
repolarization	O
of	O
the	O
previous	O
heart	O
action	O
.	O
</s>
<s>
Because	O
part	O
of	O
the	O
heart	O
muscle	O
cannot	O
be	O
excited	O
at	O
this	O
early	O
point	O
in	O
time	O
,	O
a	O
premature	O
chamber	O
action	O
can	O
trigger	O
life-threatening	O
cardiac	B-Application
arrhythmias	I-Application
(	O
e.g.	O
</s>
<s>
ventricular	O
fibrillation	O
or	O
Torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
)	O
.	O
</s>
<s>
On	O
the	O
ECG	B-Application
,	O
this	O
phenomenon	O
is	O
showing	O
when	O
a	O
ventricular	B-Error_Name
extrasystole	I-Error_Name
(	O
R	O
)	O
(	O
T-wave	B-Algorithm
)	O
is	O
superimposed	O
during	O
the	O
repolarization	O
phase	O
of	O
the	O
previous	O
action	O
of	O
the	O
heart	O
.	O
</s>
<s>
Not	O
all	O
premature	O
chamber	O
actions	O
can	O
trigger	O
these	O
dangerous	O
arrhythmias	B-Application
;	O
the	O
risk	O
is	O
increased	O
with	O
ischemia	O
of	O
the	O
heart	O
muscle	O
or	O
with	O
prolonged	O
repolarization	O
time	O
(	O
long	O
QT	O
syndrome	O
)	O
.	O
</s>
<s>
The	O
arrhythmia	B-Application
can	O
also	O
be	O
triggered	O
when	O
an	O
external	O
stimulus	O
such	O
as	O
cardioversion	O
falls	O
in	O
the	O
vulnerable	O
phase	O
of	O
the	O
cardiac	O
cycle	O
.	O
</s>
<s>
In	O
the	O
Lown	O
grading	O
system	O
of	O
ventricular	O
arrhythmias	B-Application
,	O
the	O
R-on-T	O
phenomenon	O
is	O
the	O
fifth	O
,	O
most	O
threatening	O
class	O
.	O
</s>
<s>
The	O
treatment	O
of	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
aims	O
to	O
restore	O
a	O
normal	O
rhythm	O
and	O
to	O
prevent	O
the	O
arrhythmia	B-Application
recurring	O
.	O
</s>
<s>
While	O
torsades	B-Algorithm
may	O
spontaneously	O
revert	O
to	O
a	O
normal	O
sinus	O
rhythm	O
,	O
sustained	O
torsades	B-Algorithm
requires	O
emergency	O
treatment	O
to	O
prevent	O
cardiac	O
arrest	O
.	O
</s>
<s>
The	O
most	O
effective	O
treatment	O
to	O
terminate	O
torsades	B-Algorithm
is	O
an	O
electrical	O
cardioversion	O
-	O
a	O
procedure	O
in	O
which	O
an	O
electrical	O
current	O
is	O
applied	O
across	O
the	O
heart	O
to	O
temporarily	O
stop	O
and	O
then	O
resynchronise	O
the	O
heart	O
's	O
cells	O
.	O
</s>
<s>
Treatment	O
to	O
prevent	O
recurrent	O
torsades	B-Algorithm
includes	O
infusion	O
of	O
magnesium	O
sulphate	O
,	O
correction	O
of	O
electrolyte	O
imbalances	O
such	O
as	O
low	O
blood	O
potassium	O
levels	O
(	O
hypokalaemia	O
)	O
,	O
and	O
withdrawal	O
of	O
any	O
medications	B-Algorithm
that	I-Algorithm
prolong	I-Algorithm
the	I-Algorithm
QT	I-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
Treatments	O
used	O
to	O
prevent	O
torsades	B-Algorithm
in	O
specific	O
circumstances	O
include	O
beta	O
blockers	O
or	O
mexiletine	O
in	O
long	O
QT	O
syndrome	O
.	O
</s>
<s>
Occasionally	O
a	O
pacemaker	B-Device
may	O
be	O
used	O
to	O
accelerate	O
the	O
heart	O
's	O
own	O
sinus	O
rhythm	O
,	O
and	O
those	O
at	O
risk	O
of	O
further	O
torsades	B-Algorithm
may	O
be	O
offered	O
an	O
implantable	O
defibrillator	O
to	O
automatically	O
detect	O
and	O
defibrillate	O
further	O
episodes	O
of	O
the	O
arrhythmia	B-Application
.	O
</s>
<s>
The	O
phenomenon	O
was	O
originally	O
described	O
in	O
a	O
French	O
medical	O
journal	O
by	O
Dessertenne	O
in	O
1966	O
,	O
when	O
he	O
observed	O
this	O
cardiac	B-Algorithm
rhythm	I-Algorithm
disorder	O
in	O
an	O
80-year-old	O
female	O
patient	O
with	O
complete	O
intermittent	O
atrioventricular	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
Here	O
,	O
"	O
torsade	B-Algorithm
"	O
is	O
defined	O
as	O
:	O
</s>
<s>
The	O
singular	O
and	O
plural	O
forms	O
(	O
torsade	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
,	O
torsades	B-Algorithm
de	I-Algorithm
pointes	I-Algorithm
and	O
torsades	B-Algorithm
des	I-Algorithm
pointes	I-Algorithm
)	O
have	O
all	O
often	O
been	O
used	O
.	O
</s>
<s>
One	O
group	O
of	O
physicians	O
has	O
suggested	O
that	O
it	O
would	O
make	O
the	O
most	O
sense	O
to	O
use	O
the	O
singular	O
form	O
to	O
refer	O
to	O
the	O
arrhythmia	B-Application
entity	O
(	O
where	O
an	O
arrhythmia	B-Application
may	O
involve	O
one	O
or	O
multiple	O
episodes	O
)	O
,	O
and	O
that	O
one	O
might	O
best	O
reserve	O
the	O
plural	O
form	O
for	O
describing	O
repeated	O
twisting	O
during	O
a	O
single	O
episode	O
.	O
</s>
