<s>
In	O
cardiology	O
,	O
a	O
ventricular	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
is	O
a	O
self-generated	O
electrical	O
discharge	O
initiated	O
by	O
,	O
and	O
causing	O
contraction	O
of	O
the	O
ventricles	O
of	O
the	O
heart	O
;	O
normally	O
the	O
heart	B-Algorithm
rhythm	I-Algorithm
is	O
begun	O
in	O
the	O
atria	O
of	O
the	O
heart	O
and	O
is	O
subsequently	O
transmitted	O
to	O
the	O
ventricles	O
.	O
</s>
<s>
The	O
ventricular	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
follows	O
a	O
long	O
pause	O
in	O
ventricular	O
rhythm	O
and	O
acts	O
to	O
prevent	O
cardiac	O
arrest	O
.	O
</s>
<s>
It	O
indicates	O
a	O
failure	O
of	O
the	O
electrical	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
to	O
stimulate	O
the	O
ventricles	O
(	O
which	O
would	O
lead	O
to	O
the	O
absence	O
of	O
heartbeats	O
,	O
unless	O
ventricular	B-Algorithm
escape	I-Algorithm
beats	I-Algorithm
occur	O
)	O
.	O
</s>
<s>
Ventricular	B-Algorithm
escape	I-Algorithm
beats	I-Algorithm
occur	O
when	O
the	O
rate	O
of	O
electrical	O
discharge	O
reaching	O
the	O
ventricles	O
(	O
normally	O
initiated	O
by	O
the	O
heart	O
's	O
sinoatrial	O
node	O
(	O
SA	O
node	O
)	O
,	O
transmitted	O
to	O
the	O
atrioventricular	O
node	O
(	O
AV	O
node	O
)	O
,	O
and	O
then	O
further	O
transmitted	O
to	O
the	O
ventricles	O
)	O
falls	O
below	O
the	O
base	O
rate	O
determined	O
by	O
the	O
rate	O
of	O
Phase	O
4	O
spontaneous	O
depolarisation	O
of	O
ventricular	O
pacemaker	O
cells	O
.	O
</s>
<s>
This	O
phenomenon	O
can	O
be	O
caused	O
by	O
the	O
sinoatrial	O
node	O
(	O
SA	O
node	O
)	O
failing	O
to	O
initiate	O
a	O
beat	O
,	O
by	O
a	O
failure	O
of	O
the	O
conductivity	O
from	O
the	O
SA	O
node	O
to	O
the	O
atrioventricular	O
node	O
(	O
AV	O
node	O
)	O
,	O
or	O
by	O
atrioventricular	B-Algorithm
block	I-Algorithm
(	O
especially	O
third	B-Architecture
degree	I-Architecture
AV	I-Architecture
block	I-Architecture
)	O
.	O
</s>
<s>
When	O
the	O
sinus	O
rate	O
falls	O
below	O
the	O
discharge	O
rate	O
of	O
the	O
AV	O
node	O
,	O
this	O
becomes	O
the	O
dominant	O
pacemaker	O
,	O
and	O
the	O
result	O
is	O
called	O
a	O
junctional	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
.	O
</s>
<s>
If	O
the	O
rate	O
from	O
both	O
the	O
SA	O
and	O
AV	O
node	O
fall	O
below	O
the	O
discharge	O
rate	O
of	O
ventricular	O
pacemaker	O
cells	O
,	O
a	O
ventricular	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
ensues	O
.	O
</s>
<s>
An	O
escape	O
beat	O
is	O
a	O
form	O
of	O
cardiac	B-Application
arrhythmia	I-Application
,	O
in	O
this	O
case	O
known	O
as	O
an	O
ectopic	B-Algorithm
beat	I-Algorithm
.	O
</s>
<s>
If	O
there	O
are	O
only	O
one	O
or	O
two	O
ectopic	B-Algorithm
beats	I-Algorithm
,	O
they	O
are	O
considered	O
escape	O
beats	O
.	O
</s>
<s>
If	O
this	O
causes	O
a	O
semi-normal	O
rhythm	O
to	O
arise	O
it	O
is	O
considered	O
an	O
idioventricular	B-Algorithm
rhythm	I-Algorithm
.	O
</s>
<s>
The	O
escape	O
arrhythmia	B-Application
is	O
a	O
compensatory	O
mechanism	O
that	O
indicates	O
a	O
serious	O
underlying	O
problem	O
with	O
the	O
SA	O
node	O
or	O
conduction	B-Algorithm
system	I-Algorithm
(	O
commonly	O
due	O
to	O
heart	O
attack	O
or	O
medication	O
side	O
effect	O
)	O
,	O
and	O
because	O
of	O
its	O
low	O
rate	O
,	O
it	O
can	O
cause	O
a	O
drop	O
in	O
blood	O
pressure	O
and	O
syncope	O
.	O
</s>
<s>
An	O
electrocardiogram	B-Application
can	O
be	O
used	O
to	O
identify	O
a	O
ventricular	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
.	O
</s>
<s>
The	O
QRS	O
portion	O
of	O
the	O
electrocardiogram	B-Application
represents	O
the	O
ventricular	O
depolarisation	O
;	O
in	O
normal	O
circumstances	O
the	O
QRS	O
complex	O
forms	O
a	O
sharp	O
sudden	O
peak	O
.	O
</s>
<s>
For	O
a	O
patient	O
with	O
a	O
ventricular	B-Algorithm
escape	I-Algorithm
beat	I-Algorithm
,	O
the	O
shape	O
of	O
the	O
QRS	O
complex	O
is	O
broader	O
as	O
the	O
impulse	O
can	O
not	O
travel	O
quickly	O
via	O
the	O
normal	O
electrical	O
conduction	B-Algorithm
system	I-Algorithm
.	O
</s>
<s>
Ventricular	B-Algorithm
escape	I-Algorithm
beats	I-Algorithm
differ	O
from	O
ventricular	B-Error_Name
extrasystoles	I-Error_Name
(	O
or	O
premature	B-Error_Name
ventricular	I-Error_Name
contractions	I-Error_Name
)	O
,	O
which	O
are	O
spontaneous	O
electrical	O
discharges	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
Ouabain	O
infusion	O
decreases	O
ventricular	B-Algorithm
escape	I-Algorithm
time	O
and	O
increases	O
ventricular	B-Algorithm
escape	I-Algorithm
rhythm	I-Algorithm
.	O
</s>
<s>
However	O
,	O
a	O
high	O
dose	O
of	O
ouabain	O
can	O
lead	O
to	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
