<s>
Supraventricular	B-Algorithm
tachycardia	I-Algorithm
(	O
SVT	O
)	O
is	O
an	O
umbrella	O
term	O
for	O
fast	B-Application
heart	I-Application
rhythms	I-Application
arising	O
from	O
the	O
upper	O
part	O
of	O
the	O
heart	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
the	O
other	O
group	O
of	O
fast	B-Application
heart	I-Application
rhythms	I-Application
–	O
ventricular	B-Application
tachycardia	I-Application
,	O
which	O
start	O
within	O
the	O
lower	O
chambers	O
of	O
the	O
heart	O
.	O
</s>
<s>
There	O
are	O
four	O
main	O
types	O
of	O
SVT	O
:	O
atrial	B-Application
fibrillation	I-Application
,	O
atrial	O
flutter	O
,	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
(	O
PSVT	B-Algorithm
)	O
,	O
and	O
Wolff	O
–	O
Parkinson	O
–	O
White	O
syndrome	O
.	O
</s>
<s>
The	O
symptoms	O
of	O
SVT	O
include	O
palpitations	B-Algorithm
,	O
feeling	O
of	O
faintness	O
,	O
sweating	O
,	O
shortness	O
of	O
breath	O
,	O
and/or	O
chest	O
pain	O
.	O
</s>
<s>
These	O
abnormal	O
rhythms	O
start	O
from	O
either	O
the	O
atria	O
or	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
Diagnosis	O
is	O
typically	O
by	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
,	O
holter	O
monitor	O
,	O
or	O
event	O
monitor	O
.	O
</s>
<s>
A	O
resting	O
heart	O
rate	O
of	O
more	O
than	O
100	O
beats	O
per	O
minute	O
is	O
defined	O
as	O
a	O
tachycardia	B-Application
.	O
</s>
<s>
For	O
atrial	B-Application
fibrillation	I-Application
,	O
calcium	O
channel	O
blockers	O
or	O
beta	O
blockers	O
may	O
be	O
used	O
for	O
rate	O
control	O
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
affects	O
about	O
25	O
per	O
1000	O
people	O
,	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
2.3	O
per	O
1000	O
,	O
Wolff-Parkinson-White	O
syndrome	O
2	O
per	O
1000	O
,	O
and	O
atrial	O
flutter	O
0.8	O
per	O
1000	O
.	O
</s>
<s>
Stress	O
,	O
exercise	O
,	O
and	O
emotion	O
can	O
all	O
result	O
in	O
a	O
normal	O
or	O
physiological	O
increase	B-Application
in	I-Application
heart	I-Application
rate	I-Application
,	O
but	O
they	O
can	O
precipitate	O
SVT	O
in	O
rare	O
cases	O
.	O
</s>
<s>
The	O
rapid	B-Application
heart	I-Application
rate	I-Application
,	O
if	O
fast	O
enough	O
,	O
reduces	O
the	O
opportunity	O
for	O
the	O
"	O
pump	O
"	O
to	O
fill	O
between	O
beats	O
decreasing	O
cardiac	O
output	O
and	O
consequently	O
blood	O
pressure	O
.	O
</s>
<s>
The	O
main	O
pumping	O
chamber	O
,	O
the	O
ventricle	O
,	O
is	O
protected	O
(	O
to	O
a	O
certain	O
extent	O
)	O
against	O
excessively	O
high	O
rates	O
arising	O
from	O
the	O
supraventricular	O
areas	O
by	O
a	O
"	O
gating	O
mechanism	O
"	O
at	O
the	O
atrioventricular	B-Algorithm
node	O
,	O
which	O
allows	O
only	O
a	O
proportion	O
of	O
the	O
fast	O
impulses	O
to	O
pass	O
through	O
to	O
the	O
ventricles	O
.	O
</s>
<s>
This	O
situation	O
has	O
characteristic	O
findings	O
on	O
ECG	B-Application
.	O
</s>
<s>
A	O
congenital	O
heart	O
lesion	O
,	O
Ebstein	O
's	O
anomaly	O
,	O
is	O
most	O
commonly	O
associated	O
with	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
Subtypes	O
of	O
SVT	O
can	O
often	O
be	O
distinguished	O
by	O
their	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
characteristics	O
.	O
</s>
<s>
Most	O
have	O
a	O
narrow	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
although	O
,	O
occasionally	O
,	O
electrical	O
conduction	O
abnormalities	O
may	O
produce	O
a	O
wide	O
QRS	B-Algorithm
complex	I-Algorithm
that	O
may	O
mimic	O
ventricular	B-Application
tachycardia	I-Application
(	O
VT	O
)	O
.	O
</s>
<s>
In	O
the	O
clinical	O
setting	O
,	O
the	O
distinction	O
between	O
narrow	O
and	O
wide	B-Application
complex	I-Application
tachycardia	I-Application
(	O
supraventricular	O
vs.	O
ventricular	O
)	O
is	O
fundamental	O
since	O
they	O
are	O
treated	O
differently	O
.	O
</s>
<s>
In	O
addition	O
,	O
ventricular	B-Application
tachycardia	I-Application
can	O
quickly	O
degenerate	O
into	O
ventricular	O
fibrillation	O
and	O
death	O
and	O
merits	O
different	O
consideration	O
.	O
</s>
<s>
In	O
the	O
less	O
common	O
situation	O
in	O
which	O
a	O
wide-complex	O
tachycardia	B-Application
may	O
be	O
supraventricular	O
,	O
a	O
number	O
of	O
algorithms	O
have	O
been	O
devised	O
to	O
assist	O
in	O
distinguishing	O
between	O
them	O
.	O
</s>
<s>
In	O
general	O
,	O
a	O
history	O
of	O
structural	O
heart	O
disease	O
markedly	O
increases	O
the	O
likelihood	O
that	O
the	O
tachycardia	B-Application
is	O
ventricular	O
in	O
origin	O
.	O
</s>
<s>
Sinus	B-Algorithm
tachycardia	I-Algorithm
is	O
physiologic	O
when	O
a	O
reasonable	O
stimulus	O
,	O
such	O
as	O
the	O
catecholamine	O
surge	O
associated	O
with	O
fright	O
,	O
stress	O
,	O
or	O
physical	O
activity	O
,	O
provokes	O
the	O
tachycardia	B-Application
.	O
</s>
<s>
However	O
,	O
sinus	B-Algorithm
tachycardia	I-Algorithm
is	O
considered	O
part	O
of	O
the	O
diagnoses	O
included	O
in	O
SVT	O
by	O
most	O
sources	O
.	O
</s>
<s>
Sinoatrial	O
node	O
reentrant	O
tachycardia	B-Application
(	O
SANRT	O
)	O
is	O
caused	O
by	O
a	O
reentry	O
circuit	O
localised	O
to	O
the	O
SA	O
node	O
,	O
resulting	O
in	O
a	O
P-wave	B-Algorithm
of	O
normal	O
shape	O
and	O
size	O
(	O
morphology	O
)	O
that	O
falls	O
before	O
a	O
regular	O
,	O
narrow	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
It	O
cannot	O
be	O
distinguished	O
electrocardiographically	O
from	O
sinus	B-Algorithm
tachycardia	I-Algorithm
unless	O
the	O
sudden	O
onset	O
is	O
observed	O
(	O
or	O
recorded	O
on	O
a	O
continuous	O
monitoring	O
device	O
)	O
.	O
</s>
<s>
Ectopic	O
(	O
unifocal	O
)	O
atrial	B-Algorithm
tachycardia	I-Algorithm
arises	O
from	O
an	O
independent	O
focus	O
within	O
the	O
atria	O
,	O
distinguished	O
by	O
a	O
consistent	O
P-wave	B-Algorithm
of	O
abnormal	O
shape	O
and/or	O
size	O
that	O
falls	O
before	O
a	O
narrow	O
,	O
regular	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
Some	O
atrial	B-Algorithm
tachycardias	I-Algorithm
,	O
rather	O
than	O
being	O
a	O
result	O
of	O
increased	O
automaticity	O
may	O
be	O
a	O
result	O
of	O
a	O
micro-reentrant	O
circuit	O
(	O
defined	O
by	O
some	O
as	O
less	O
than	O
2cm	O
in	O
longest	O
diameter	O
to	O
distinguish	O
it	O
from	O
macro-reentrant	O
atrial	O
flutter	O
)	O
.	O
</s>
<s>
Still	O
other	O
atrial	B-Algorithm
tachycardias	I-Algorithm
may	O
be	O
due	O
to	O
triggered	O
activity	O
caused	O
by	O
after-depolarizations	O
.	O
</s>
<s>
Multifocal	B-Algorithm
atrial	I-Algorithm
tachycardia	I-Algorithm
(	O
MAT	O
)	O
is	O
tachycardia	B-Application
arising	O
from	O
at	O
least	O
three	O
ectopic	B-Algorithm
foci	I-Algorithm
within	O
the	O
atria	O
,	O
distinguished	O
by	O
P-waves	O
of	O
at	O
least	O
three	O
different	O
morphologies	O
that	O
all	O
fall	O
before	O
irregular	O
,	O
narrow	B-Algorithm
QRS	I-Algorithm
complexes	I-Algorithm
.	O
</s>
<s>
Atrial	B-Application
fibrillation	I-Application
meets	O
the	O
definition	O
of	O
SVT	O
when	O
associated	O
with	O
a	O
ventricular	O
response	O
greater	O
than	O
100	O
beats	O
per	O
minute	O
.	O
</s>
<s>
It	O
is	O
characterized	O
as	O
an	O
"	O
irregularly	O
,	O
irregular	O
rhythm	O
"	O
both	O
in	O
its	O
atrial	O
and	O
ventricular	B-Application
depolarizations	I-Application
and	O
is	O
distinguished	O
by	O
its	O
fibrillatory	O
atrial	O
waves	O
that	O
,	O
at	O
some	O
point	O
in	O
their	O
chaos	O
,	O
stimulate	O
a	O
response	O
from	O
the	O
ventricles	O
in	O
the	O
form	O
of	O
irregular	O
,	O
narrow	B-Algorithm
QRS	I-Algorithm
complexes	I-Algorithm
.	O
</s>
<s>
On	O
the	O
ECG	B-Application
this	O
appears	O
as	O
a	O
line	O
of	O
"	O
sawtooth	O
"	O
waves	O
preceding	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
The	O
AV	O
node	O
will	O
not	O
usually	O
conduct	O
300	O
beats	O
per	O
minute	O
so	O
the	O
P:QRS	O
ratio	O
is	O
usually	O
2:1	O
or	O
4:1	O
pattern	O
,	O
(	O
though	O
rarely	O
3:1	O
,	O
and	O
sometimes	O
1:1	O
where	O
class	O
IC	O
antiarrhythmic	B-Algorithm
drug	I-Algorithm
are	O
in	O
use	O
)	O
.	O
</s>
<s>
Because	O
the	O
ratio	O
of	O
P	O
to	O
QRS	B-Algorithm
is	O
usually	O
consistent	O
,	O
A-flutter	O
is	O
often	O
regular	O
in	O
comparison	O
to	O
its	O
irregular	O
counterpart	O
,	O
atrial	B-Application
fibrillation	I-Application
.	O
</s>
<s>
Atrial	O
flutter	O
is	O
also	O
not	O
necessarily	O
a	O
tachycardia	B-Application
by	O
definition	O
unless	O
the	O
AV	O
node	O
permits	O
a	O
ventricular	O
response	O
greater	O
than	O
100	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
involves	O
a	O
reentry	O
circuit	O
forming	O
next	O
to	O
,	O
or	O
within	O
,	O
the	O
AV	O
node	O
.	O
</s>
<s>
Because	O
the	O
node	O
is	O
immediately	O
between	O
the	O
atria	O
and	O
ventricle	O
,	O
the	O
re-entry	O
circuit	O
often	O
stimulates	O
both	O
,	O
appearing	O
as	O
a	O
backward	O
(	O
retrograde	O
)	O
conducted	O
P-wave	B-Algorithm
buried	O
within	O
or	O
occurring	O
just	O
after	O
the	O
regular	O
,	O
narrow	B-Algorithm
QRS	I-Algorithm
complexes	I-Algorithm
.	O
</s>
<s>
Atrioventricular	B-Algorithm
reciprocating	I-Algorithm
tachycardia	I-Algorithm
(	O
AVRT	B-Algorithm
)	O
,	O
also	O
results	O
from	O
a	O
reentry	O
circuit	O
,	O
although	O
one	O
physically	O
much	O
larger	O
than	O
AVNRT	B-Algorithm
.	O
</s>
<s>
In	O
orthodromic	O
AVRT	B-Algorithm
,	O
atrial	O
impulses	O
are	O
conducted	O
down	O
through	O
the	O
AV	O
node	O
and	O
retrogradely	O
re-enter	O
the	O
atrium	O
via	O
the	O
accessory	O
pathway	O
.	O
</s>
<s>
A	O
distinguishing	O
characteristic	O
of	O
orthodromic	O
AVRT	B-Algorithm
can	O
therefore	O
be	O
an	O
inverted	O
P-wave	B-Algorithm
(	O
relative	O
to	O
a	O
sinus	O
P	B-Algorithm
wave	I-Algorithm
)	O
that	O
follows	O
each	O
of	O
its	O
regular	O
,	O
narrow	B-Algorithm
QRS	I-Algorithm
complexes	I-Algorithm
,	O
due	O
to	O
retrograde	O
conduction	O
.	O
</s>
<s>
In	O
antidromic	O
AVRT	B-Algorithm
,	O
atrial	O
impulses	O
are	O
conducted	O
down	O
through	O
the	O
accessory	O
pathway	O
and	O
re-enter	O
the	O
atrium	O
retrogradely	O
via	O
the	O
AV	O
node	O
.	O
</s>
<s>
Because	O
the	O
accessory	O
pathway	O
initiates	O
conduction	O
in	O
the	O
ventricles	O
outside	O
of	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
in	O
antidromic	O
AVRT	B-Algorithm
is	O
wider	O
than	O
usual	O
.	O
</s>
<s>
A	O
delta	O
wave	O
is	O
an	O
initial	O
slurred	O
deflection	O
seen	O
in	O
the	O
initial	O
part	O
of	O
an	O
otherwise	O
narrow	O
QRS	B-Algorithm
of	O
a	O
patient	O
at	O
risk	O
for	O
WPW	O
and	O
is	O
an	O
indicator	O
of	O
the	O
presence	O
of	O
an	O
accessory	O
pathway	O
.	O
</s>
<s>
Once	O
an	O
antidromic	O
AVRT	B-Algorithm
tachycardia	B-Application
is	O
initiated	O
,	O
it	O
is	O
no	O
longer	O
delta	O
waves	O
but	O
rather	O
a	O
wide	O
complex	O
(	O
>120	O
ms	O
)	O
tachycardia	B-Application
that	O
is	O
seen	O
.	O
</s>
<s>
Junctional	B-Algorithm
ectopic	I-Algorithm
tachycardia	I-Algorithm
(	O
JET	O
)	O
is	O
a	O
rare	O
tachycardia	B-Application
caused	O
by	O
increased	O
automaticity	O
of	O
the	O
AV	O
node	O
itself	O
initiating	O
frequent	O
heartbeats	O
.	O
</s>
<s>
On	O
the	O
ECG	B-Application
,	O
junctional	O
tachycardia	B-Application
often	O
presents	O
with	O
abnormal	O
morphology	O
P-waves	O
that	O
may	O
fall	O
anywhere	O
in	O
relation	O
to	O
a	O
regular	O
,	O
narrow	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
The	O
following	O
types	O
of	O
supraventricular	B-Algorithm
tachycardias	I-Algorithm
are	O
more	O
precisely	O
classified	O
by	O
their	O
specific	O
site	O
of	O
origin	O
.	O
</s>
<s>
Atrioventricular	B-Algorithm
origin	O
:	O
</s>
<s>
A	O
variety	O
of	O
drugs	O
including	O
simple	O
AV	O
nodal	O
blocking	O
agents	O
such	O
as	O
beta-blockers	O
and	O
verapamil	O
,	O
as	O
well	O
as	O
antiarrhythmic	B-Algorithm
drugs	I-Algorithm
may	O
be	O
used	O
,	O
usually	O
with	O
good	O
effect	O
,	O
although	O
the	O
adverse	O
effects	O
of	O
these	O
therapies	O
need	O
to	O
be	O
weighed	O
against	O
potential	O
benefits	O
.	O
</s>
<s>
Radiofrequency	O
ablation	O
has	O
revolutionized	O
the	O
treatment	O
of	O
tachycardia	B-Application
caused	O
by	O
a	O
re-entrant	O
pathway	O
.	O
</s>
<s>
Ablation	O
has	O
been	O
shown	O
to	O
be	O
highly	O
effective	O
:	O
around	O
90%	O
in	O
the	O
case	O
of	O
AVNRT	B-Algorithm
.	O
</s>
<s>
Similar	O
high	O
rates	O
of	O
success	O
are	O
achieved	O
with	O
AVRT	B-Algorithm
and	O
typical	O
atrial	O
flutter	O
.	O
</s>
<s>
This	O
therapy	O
has	O
further	O
improved	O
the	O
treatment	O
options	O
for	O
AVNRT	B-Algorithm
(	O
and	O
other	O
SVTs	O
with	O
pathways	O
close	O
to	O
the	O
AV	O
node	O
)	O
,	O
widening	O
the	O
application	O
of	O
curative	O
ablation	O
to	O
young	O
patients	O
with	O
relatively	O
mild	O
but	O
still	O
troublesome	O
symptoms	O
who	O
might	O
not	O
have	O
accepted	O
the	O
risk	O
of	O
requiring	O
a	O
pacemaker	O
.	O
</s>
<s>
Most	O
SVTs	O
are	O
unpleasant	O
rather	O
than	O
life-threatening	O
,	O
although	O
very	O
fast	B-Application
heart	I-Application
rates	I-Application
can	O
be	O
problematic	O
for	O
those	O
with	O
underlying	O
ischemic	O
heart	O
disease	O
,	O
or	O
the	O
elderly	O
.	O
</s>
<s>
Lifestyle	O
changes	O
,	O
medication	O
and	O
heart	O
procedures	O
may	O
be	O
needed	O
to	O
control	O
or	O
eliminate	O
the	O
rapid	B-Application
heartbeats	I-Application
and	O
related	O
symptoms	O
.	O
</s>
<s>
Acute	O
attacks	O
of	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
are	O
treated	O
with	O
Esmolol	O
(	O
i.v.	O
</s>
