<s>
Bigeminy	B-Algorithm
is	O
a	O
cardiac	B-Application
arrhythmia	I-Application
in	O
which	O
there	O
is	O
a	O
single	O
ectopic	B-Algorithm
beat	I-Algorithm
,	O
or	O
irregular	B-Application
heartbeat	I-Application
,	O
following	O
each	O
regular	O
heartbeat	O
.	O
</s>
<s>
Most	O
often	O
this	O
is	O
due	O
to	O
ectopic	B-Algorithm
beats	I-Algorithm
occurring	O
so	O
frequently	O
that	O
there	O
is	O
one	O
after	O
each	O
sinus	O
beat	O
,	O
or	O
normal	O
heartbeat	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
ventricular	B-Algorithm
bigeminy	I-Algorithm
,	O
a	O
sinus	O
beat	O
is	O
shortly	O
followed	O
by	O
a	O
premature	B-Error_Name
ventricular	I-Error_Name
contraction	I-Error_Name
(	O
PVC	B-Error_Name
)	O
,	O
a	O
pause	O
,	O
another	O
normal	O
beat	O
,	O
and	O
then	O
another	O
PVC	B-Error_Name
.	O
</s>
<s>
In	O
atrial	O
bigeminy	B-Algorithm
,	O
the	O
other	O
"	O
twin	O
"	O
is	O
a	O
premature	B-Algorithm
atrial	I-Algorithm
contraction	I-Algorithm
(	O
PAC	O
)	O
.	O
</s>
<s>
After	O
any	O
PVC	B-Error_Name
there	O
is	O
a	O
pause	O
that	O
can	O
lead	O
to	O
the	O
development	O
of	O
bigeminy	B-Algorithm
.	O
</s>
<s>
A	O
PVC	B-Error_Name
wavefront	O
often	O
encounters	O
a	O
refractory	O
AV	O
node	O
that	O
does	O
not	O
conduct	O
the	O
wavefront	O
retrograde	O
.	O
</s>
<s>
Since	O
the	O
sinus	O
P	O
wave	O
to	O
PVC	B-Error_Name
interval	O
is	O
less	O
than	O
the	O
normal	O
P	O
–	O
P	O
interval	O
,	O
the	O
interval	O
between	O
the	O
PVC	B-Error_Name
and	O
the	O
next	O
P	O
wave	O
is	O
prolonged	O
to	O
equal	O
the	O
normal	O
time	O
elapsed	O
during	O
two	O
P	O
–	O
P	O
intervals	O
.	O
</s>
<s>
The	O
pause	O
after	O
the	O
PVC	B-Error_Name
leads	O
to	O
a	O
longer	O
recovery	O
time	O
,	O
which	O
is	O
associated	O
with	O
a	O
higher	O
likelihood	O
of	O
myocardium	O
being	O
in	O
different	O
stages	O
of	O
repolarization	O
.	O
</s>
<s>
This	O
then	O
allows	O
for	O
re-entrant	B-Algorithm
circuits	I-Algorithm
and	O
sets	O
up	O
the	O
ventricle	O
for	O
another	O
PVC	B-Error_Name
after	O
the	O
next	O
sinus	O
beat	O
.	O
</s>
<s>
The	O
constant	O
interval	O
between	O
the	O
sinus	O
beat	O
and	O
PVC	B-Error_Name
suggests	O
a	O
reentrant	O
etiology	O
rather	O
than	O
spontaneous	O
automaticity	O
of	O
the	O
ventricle	O
.	O
</s>
<s>
Premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
by	O
contrast	O
do	O
not	O
have	O
a	O
compensatory	O
pause	O
,	O
since	O
they	O
reset	O
the	O
sinus	O
node	O
,	O
but	O
atrial	O
or	O
supraventricular	O
bigeminy	B-Algorithm
can	O
occur	O
.	O
</s>
<s>
When	O
the	O
atrial	O
rhythm	O
is	O
irregular	O
(	O
as	O
in	O
atrial	O
fibrillation	O
or	O
sinus	O
arrythmia	B-Application
)	O
the	O
presence	O
of	O
bigeminy	B-Algorithm
depends	O
on	O
the	O
length	O
of	O
the	O
P	O
–	O
P	O
interval	O
and	O
happens	O
more	O
frequently	O
with	O
a	O
longer	O
interval	O
.	O
</s>
<s>
As	O
with	O
post	O
PVC	B-Error_Name
pauses	O
,	O
a	O
longer	O
P	O
–	O
P	O
interval	O
leads	O
to	O
a	O
higher	O
chance	O
of	O
re-entrant	B-Algorithm
circuits	I-Algorithm
and	O
thus	O
PVCs	O
.	O
</s>
<s>
The	O
term	O
"	O
rule	O
of	O
bigeminy	B-Algorithm
"	O
is	O
used	O
to	O
refer	O
to	O
the	O
dependence	O
of	O
bigeminy	B-Algorithm
on	O
the	O
ventricular	O
cycle	O
length	O
in	O
irregular	O
rhythms	O
.	O
</s>
<s>
If	O
every	O
other	O
beat	O
is	O
abnormal	O
,	O
it	O
is	O
described	O
as	O
bigeminal	B-Algorithm
.	O
</s>
<s>
Bigeminy	B-Algorithm
is	O
contrasted	O
with	O
couplets	O
,	O
which	O
are	O
paired	O
abnormal	O
beats	O
.	O
</s>
<s>
Groups	O
of	O
three	O
abnormal	O
beats	O
are	O
called	O
triplets	O
and	O
are	O
considered	O
a	O
brief	O
run	O
of	O
non-sustained	O
ventricular	B-Application
tachycardia	I-Application
(	O
NSVT	B-Application
)	O
,	O
and	O
if	O
the	O
grouping	O
lasts	O
for	O
more	O
than	O
30	O
seconds	O
,	O
it	O
is	O
ventricular	B-Application
tachycardia	I-Application
(	O
VT	O
)	O
.	O
</s>
<s>
In	O
people	O
without	O
underlying	O
heart	O
disease	O
and	O
who	O
do	O
not	O
have	O
any	O
symptoms	O
,	O
bigeminy	B-Algorithm
in	O
itself	O
does	O
not	O
require	O
any	O
treatment	O
.	O
</s>
<s>
Class	B-Algorithm
I	I-Algorithm
and	I-Algorithm
III	I-Algorithm
agents	O
are	O
generally	O
avoided	O
as	O
they	O
can	O
provoke	O
more	O
serious	O
arrhythmias	B-Application
.	O
</s>
