<s>
AV-nodal	O
reentrant	O
tachycardia	B-Application
(	O
AVNRT	B-Algorithm
)	O
is	O
a	O
type	O
of	O
abnormal	O
fast	B-Application
heart	I-Application
rhythm	I-Application
.	O
</s>
<s>
It	O
is	O
a	O
type	O
of	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
(	O
SVT	O
)	O
,	O
meaning	O
that	O
it	O
originates	O
from	O
a	O
location	O
within	O
the	O
heart	O
above	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
.	O
</s>
<s>
AV	B-Algorithm
nodal	I-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
is	O
the	O
most	O
common	O
regular	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
The	O
main	O
symptom	O
is	O
palpitations	B-Algorithm
.	O
</s>
<s>
AVNRT	B-Algorithm
occurs	O
when	O
a	O
reentrant	O
circuit	O
forms	O
within	O
or	O
just	O
next	O
to	O
the	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
The	O
fast	O
and	O
slow	O
pathways	O
should	O
not	O
be	O
confused	O
with	O
the	O
accessory	B-Algorithm
pathways	I-Algorithm
that	O
give	O
rise	O
to	O
Wolff-Parkinson-White	O
syndrome	O
(	O
WPW	O
syndrome	O
)	O
or	O
atrioventricular	B-Algorithm
reciprocating	I-Algorithm
tachycardia	I-Algorithm
(	O
AVRT	B-Algorithm
)	O
.	O
</s>
<s>
In	O
AVNRT	B-Algorithm
,	O
the	O
fast	O
and	O
slow	O
pathways	O
are	O
located	O
within	O
the	O
right	O
atrium	O
close	O
to	O
or	O
within	O
the	O
AV	O
node	O
and	O
exhibit	O
electrophysiologic	B-Application
properties	O
similar	O
to	O
AV	O
nodal	O
tissue	O
.	O
</s>
<s>
Accessory	B-Algorithm
pathways	I-Algorithm
that	O
give	O
rise	O
to	O
WPW	O
syndrome	O
and	O
AVRT	B-Algorithm
are	O
located	O
in	O
the	O
atrioventricular	B-Algorithm
valvular	O
rings	O
.	O
</s>
<s>
They	O
provide	O
a	O
direct	O
connection	O
between	O
the	O
atria	O
and	O
ventricles	O
,	O
and	O
have	O
electrophysiologic	B-Application
properties	O
similar	O
to	O
muscular	O
heart	O
tissue	O
of	O
the	O
heart	O
's	O
ventricles	O
.	O
</s>
<s>
The	O
main	O
symptom	O
of	O
AVNRT	B-Algorithm
is	O
the	O
sudden	O
development	O
of	O
rapid	O
regular	O
palpitations	B-Algorithm
.	O
</s>
<s>
These	O
palpitations	B-Algorithm
may	O
be	O
associated	O
with	O
a	O
fluttering	O
sensation	O
in	O
the	O
neck	O
,	O
caused	O
by	O
near-simultaneous	O
contraction	O
of	O
the	O
atria	O
and	O
ventricles	O
against	O
a	O
closed	O
tricuspid	O
valve	O
leading	O
to	O
the	O
pressure	O
or	O
atrial	O
contraction	O
being	O
transmitted	O
backwards	O
into	O
the	O
venous	O
system	O
.	O
</s>
<s>
The	O
rapid	B-Application
heart	I-Application
rate	I-Application
may	O
lead	O
to	O
feelings	O
of	O
anxiety	O
,	O
and	O
may	O
therefore	O
be	O
mistaken	O
for	O
panic	O
attacks	O
.	O
</s>
<s>
Someone	O
with	O
underlying	O
coronary	O
artery	O
disease	O
(	O
narrowing	O
of	O
the	O
arteries	O
of	O
the	O
heart	O
by	O
atherosclerosis	O
)	O
who	O
has	O
a	O
very	O
rapid	B-Application
heart	I-Application
rate	I-Application
may	O
experience	O
chest	O
pain	O
similar	O
to	O
angina	O
;	O
this	O
pain	O
is	O
band	O
-	O
or	O
pressure-like	O
around	O
the	O
chest	O
and	O
often	O
radiates	O
to	O
the	O
left	O
arm	O
and	O
angle	O
of	O
the	O
left	O
jaw	O
.	O
</s>
<s>
Symptoms	O
often	O
occur	O
without	O
any	O
specific	O
trigger	O
,	O
although	O
some	O
find	O
that	O
their	O
palpitations	B-Algorithm
often	O
occur	O
after	O
lifting	O
heavy	O
items	O
or	O
bending	O
forwards	O
.	O
</s>
<s>
The	O
onset	O
of	O
palpitations	B-Algorithm
is	O
sudden	O
,	O
with	O
the	O
acceleration	O
of	O
the	O
heart	O
rate	O
occurring	O
within	O
a	O
single	O
beat	O
,	O
and	O
may	O
be	O
preceded	O
by	O
a	O
feeling	O
of	O
the	O
heart	O
skipping	O
a	O
beat	O
.	O
</s>
<s>
During	O
AVNRT	B-Algorithm
the	O
heart	O
rate	O
is	O
typically	O
between	O
140	O
and	O
280	O
beats	O
per	O
minute	O
.	O
</s>
<s>
The	O
fundamental	O
mechanism	O
of	O
AVNRT	B-Algorithm
is	O
a	O
presence	O
of	O
a	O
dual	O
atrioventricular	B-Algorithm
node	O
physiology	O
(	O
present	O
in	O
half	O
of	O
the	O
population	O
)	O
,	O
which	O
acts	O
as	O
a	O
re-entrant	O
circuit	O
within	O
the	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
"	O
Typical	O
"	O
,	O
"	O
common	O
"	O
,	O
or	O
"	O
slow-fast	O
"	O
AVNRT	B-Algorithm
uses	O
the	O
slow	O
AV	O
nodal	O
pathway	O
to	O
conduct	O
towards	O
the	O
ventricle	O
(	O
the	O
anterograde	O
limb	O
of	O
the	O
circuit	O
)	O
and	O
the	O
fast	O
AV	O
nodal	O
pathway	O
to	O
conduct	O
to	O
the	O
atria	O
(	O
the	O
retrograde	O
limb	O
)	O
.	O
</s>
<s>
The	O
re-entrant	O
circuit	O
can	O
be	O
reversed	O
such	O
that	O
the	O
fast	O
AV	O
nodal	O
pathway	O
is	O
the	O
anterograde	O
limb	O
and	O
the	O
slow	O
AV	O
nodal	O
pathway	O
is	O
the	O
retrograde	O
limb	O
,	O
referred	O
to	O
as	O
"	O
atypical	O
"	O
,	O
"	O
uncommon	O
"	O
,	O
or	O
"	O
fast-slow	O
"	O
AVNRT	B-Algorithm
.	O
</s>
<s>
Atypical	O
AVNRT	B-Algorithm
may	O
also	O
use	O
the	O
slow	O
AV	O
nodal	O
pathway	O
as	O
the	O
anterograde	O
limb	O
and	O
left	O
atrial	O
fibres	O
that	O
approach	O
the	O
AV	O
node	O
from	O
the	O
left	O
side	O
of	O
the	O
inter-atrial	O
septum	O
as	O
the	O
retrograde	O
limb	O
,	O
and	O
is	O
sometimes	O
referred	O
to	O
as	O
"	O
slow-slow	O
"	O
AVNRT	B-Algorithm
.	O
</s>
<s>
In	O
typical	O
AVNRT	B-Algorithm
,	O
the	O
anterograde	O
conduction	O
is	O
via	O
the	O
slow	O
pathway	O
and	O
the	O
retrograde	O
conduction	O
is	O
via	O
the	O
fast	O
pathway	O
(	O
"	O
slow-fast	O
"	O
AVNRT	B-Algorithm
)	O
.	O
</s>
<s>
The	O
RP	O
interval	O
is	O
often	O
so	O
short	O
that	O
the	O
inverted	O
P	O
waves	O
may	O
not	O
be	O
seen	O
on	O
the	O
surface	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
as	O
they	O
are	O
buried	O
within	O
or	O
immediately	O
after	O
the	O
QRS	O
complexes	O
,	O
appearing	O
as	O
a	O
"	O
pseudo	O
R	O
prime	O
"	O
wave	O
in	O
lead	O
V1	O
or	O
a	O
"	O
pseudo	O
S	O
"	O
wave	O
in	O
the	O
inferior	O
leads	O
.	O
</s>
<s>
In	O
atypical	O
AVNRT	B-Algorithm
,	O
the	O
anterograde	O
conduction	O
is	O
via	O
the	O
fast	O
pathway	O
and	O
the	O
retrograde	O
conduction	O
is	O
via	O
the	O
slow	O
pathway	O
(	O
"	O
fast-slow	O
"	O
AVNRT	B-Algorithm
)	O
.	O
</s>
<s>
(	O
"	O
slow-slow	O
"	O
AVNRT	B-Algorithm
)	O
.Because	O
the	O
retrograde	O
conduction	O
is	O
via	O
the	O
slow	O
pathway	O
,	O
stimulation	O
of	O
the	O
atria	O
will	O
be	O
delayed	O
by	O
the	O
slow	O
conduction	O
tissue	O
and	O
will	O
typically	O
produce	O
an	O
inverted	O
P	O
wave	O
that	O
falls	O
after	O
the	O
QRS	O
complex	O
on	O
the	O
surface	O
ECG	B-Application
.	O
</s>
<s>
If	O
the	O
symptoms	O
are	O
present	O
while	O
the	O
person	O
is	O
receiving	O
medical	O
care	O
(	O
e.g.	O
,	O
in	O
an	O
emergency	O
department	O
)	O
,	O
an	O
ECG	B-Application
may	O
show	O
typical	O
changes	O
that	O
confirm	O
the	O
diagnosis	O
i.e.	O
,	O
QRS	O
duration	O
<	O
120	O
ms	O
,	O
unless	O
a	O
heart	B-Algorithm
block	I-Algorithm
is	O
suspected	O
.	O
</s>
<s>
If	O
the	O
palpitations	B-Algorithm
are	O
recurrent	O
,	O
a	O
doctor	O
may	O
request	O
a	O
Holter	O
monitor	O
(	O
portable	O
,	O
wearable	O
ECG	B-Application
recorder	O
)	O
.	O
</s>
<s>
In	O
rare	O
cases	O
,	O
disabling	O
but	O
infrequent	O
episodes	O
of	O
palpitations	B-Algorithm
may	O
require	O
the	O
insertion	O
of	O
a	O
small	O
device	O
under	O
the	O
skin	O
that	O
continuously	O
record	O
heart	O
activity	O
(	O
an	O
implantable	O
loop	O
recorder	O
)	O
.	O
</s>
<s>
All	O
these	O
ECG-based	O
technologies	O
also	O
enable	O
the	O
distinction	O
between	O
AVNRT	B-Algorithm
and	O
other	O
abnormal	O
fast	O
heart	O
rhythms	O
such	O
as	O
atrial	B-Application
fibrillation	I-Application
,	O
atrial	O
flutter	O
,	O
sinus	B-Algorithm
tachycardia	I-Algorithm
,	O
ventricular	B-Application
tachycardia	I-Application
and	O
tachyarrhythmias	B-Application
related	O
to	O
Wolff-Parkinson-White	O
syndrome	O
,	O
all	O
of	O
which	O
may	O
have	O
symptoms	O
that	O
are	O
similar	O
to	O
AVNRT	B-Algorithm
.	O
</s>
<s>
Blood	O
tests	O
commonly	O
performed	O
in	O
people	O
with	O
palpitations	B-Algorithm
are	O
:	O
</s>
<s>
Treatments	O
for	O
AVNRT	B-Algorithm
aim	O
to	O
terminate	O
episodes	O
of	O
tachycardia	B-Application
,	O
and	O
to	O
prevent	O
further	O
episodes	O
from	O
occurring	O
in	O
the	O
future	O
.	O
</s>
<s>
An	O
episode	O
of	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
due	O
to	O
AVNRT	B-Algorithm
can	O
be	O
terminated	O
by	O
any	O
action	O
that	O
transiently	O
blocks	O
the	O
AV	O
node	O
.	O
</s>
<s>
Some	O
of	O
those	O
with	O
AVNRT	B-Algorithm
may	O
be	O
able	O
to	O
stop	O
their	O
attack	O
by	O
using	O
physical	O
manoeuvres	O
that	O
increase	O
the	O
activity	O
of	O
the	O
vagus	O
nerve	O
on	O
the	O
heart	O
,	O
specifically	O
on	O
the	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
Medications	O
that	O
slow	O
or	O
briefly	O
halt	O
electrical	O
conduction	O
through	O
the	O
AV	O
node	O
can	O
terminate	O
AVNRT	B-Algorithm
,	O
including	O
adenosine	O
,	O
beta	O
blockers	O
,	O
or	O
non-dihydropyridine	O
calcium	O
channel	O
blockers	O
(	O
such	O
as	O
verapamil	O
or	O
diltiazem	O
)	O
.	O
</s>
<s>
If	O
the	O
fast	B-Application
heart	I-Application
rate	I-Application
is	O
poorly	O
tolerated	O
(	O
e.g.	O
</s>
<s>
the	O
development	O
of	O
heart	O
failure	O
symptoms	O
,	O
low	O
blood	O
pressure	O
or	O
coma	O
)	O
then	O
AVNRT	B-Algorithm
can	O
be	O
terminated	O
electrically	O
using	O
a	O
cardioversion	O
.	O
</s>
<s>
While	O
preventative	O
treatment	O
may	O
be	O
very	O
helpful	O
at	O
stopping	O
the	O
unpleasant	O
symptoms	O
associated	O
with	O
AVNRT	B-Algorithm
,	O
as	O
this	O
arrhythmia	O
is	O
a	O
benign	O
condition	O
,	O
preventative	O
treatment	O
is	O
not	O
essential	O
.	O
</s>
<s>
Alternatively	O
,	O
an	O
invasive	O
procedure	O
called	O
an	O
electrophysiology	B-Application
(	O
EP	O
)	O
study	O
and	O
catheter	O
ablation	O
can	O
be	O
used	O
to	O
confirm	O
the	O
diagnosis	O
and	O
potentially	O
offer	O
a	O
cure	O
.	O
</s>
<s>
The	O
tip	O
of	O
one	O
of	O
these	O
catheters	O
can	O
be	O
used	O
to	O
heat	O
or	O
freeze	O
the	O
slow	O
pathway	O
of	O
the	O
AV	O
node	O
,	O
destroying	O
its	O
ability	O
to	O
conduct	O
electrical	O
impulses	O
,	O
and	O
preventing	O
AVNRT	B-Algorithm
.	O
</s>
<s>
Catheter	O
ablation	O
of	O
the	O
slow	O
pathway	O
,	O
if	O
successfully	O
carried	O
out	O
,	O
can	O
potentially	O
cure	O
AVNRT	B-Algorithm
with	O
success	O
rates	O
of	O
>95	O
%	O
,	O
balanced	O
against	O
a	O
small	O
risk	O
of	O
complications	O
including	O
damaging	O
the	O
AV	O
node	O
and	O
subsequently	O
requiring	O
a	O
pacemaker	B-Device
.	O
</s>
