<s>
Premature	B-Algorithm
atrial	I-Algorithm
contraction	I-Algorithm
(	O
PAC	O
)	O
,	O
also	O
known	O
as	O
atrial	B-Algorithm
premature	I-Algorithm
complexes	I-Algorithm
(	O
APC	O
)	O
or	O
atrial	B-Algorithm
premature	I-Algorithm
beats	I-Algorithm
(	O
APB	O
)	O
,	O
are	O
a	O
common	O
cardiac	B-Application
dysrhythmia	I-Application
characterized	O
by	O
premature	O
heartbeats	O
originating	O
in	O
the	O
atria	O
.	O
</s>
<s>
While	O
the	O
sinoatrial	O
node	O
typically	O
regulates	O
the	O
heartbeat	O
during	O
normal	O
sinus	O
rhythm	O
,	O
PACs	O
occur	O
when	O
another	B-Algorithm
region	I-Algorithm
of	I-Algorithm
the	I-Algorithm
atria	I-Algorithm
depolarizes	I-Algorithm
before	O
the	O
sinoatrial	O
node	O
and	O
thus	O
triggers	O
a	O
premature	O
heartbeat	O
,	O
in	O
contrast	O
to	O
escape	O
beats	O
,	O
in	O
which	O
the	O
normal	O
sinoatrial	O
node	O
fails	O
,	O
leaving	O
a	O
non-nodal	O
pacemaker	O
to	O
initiate	O
a	O
late	O
beat	O
.	O
</s>
<s>
PACs	O
are	O
often	O
completely	O
asymptomatic	O
and	O
may	O
be	O
noted	O
only	O
with	O
Holter	O
monitoring	O
,	O
but	O
occasionally	O
they	O
can	O
be	O
perceived	O
as	O
a	O
skipped	B-Algorithm
beat	I-Algorithm
or	O
a	O
jolt	O
in	O
the	O
chest	O
.	O
</s>
<s>
Often	O
,	O
hypertension	O
goes	O
hand	O
in	O
hand	O
with	O
various	O
atrial	B-Application
fibrillations	I-Application
including	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
(	O
PACs	O
)	O
.	O
</s>
<s>
Additional	O
factors	O
that	O
may	O
contribute	O
to	O
spontaneous	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
could	O
be	O
:	O
</s>
<s>
Premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
are	O
typically	O
diagnosed	O
with	O
an	O
electrocardiogram	B-Application
,	O
Holter	O
monitor	O
,	O
cardiac	O
event	O
monitor	O
,	O
or	O
with	O
a	O
smartwatch	B-Application
with	O
an	O
ECG	B-Application
functionality	O
.	O
</s>
<s>
On	O
an	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
,	O
PACs	O
are	O
characterized	O
by	O
an	O
abnormally	O
shaped	O
P	B-Algorithm
wave	I-Algorithm
in	O
different	O
ECG	B-Application
leads	O
.	O
</s>
<s>
Since	O
the	O
premature	B-Algorithm
beat	I-Algorithm
initiates	O
outside	O
the	O
sinoatrial	O
node	O
,	O
the	O
associated	O
P	B-Algorithm
wave	I-Algorithm
appears	O
different	O
from	O
those	O
seen	O
in	O
normal	O
sinus	O
rhythm	O
.	O
</s>
<s>
Typically	O
,	O
the	O
atrial	O
impulse	O
propagates	O
normally	O
through	O
the	O
atrioventricular	O
node	O
and	O
into	O
the	O
cardiac	O
ventricles	O
,	O
resulting	O
in	O
a	O
normal	O
,	O
narrow	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
However	O
,	O
if	O
the	O
atrial	O
beat	O
is	O
premature	O
enough	O
,	O
it	O
may	O
reach	O
the	O
atrioventricular	O
node	O
during	O
its	O
refractory	O
period	O
,	O
in	O
which	O
case	O
it	O
will	O
not	O
be	O
conducted	O
to	O
the	O
ventricle	O
and	O
there	O
will	O
be	O
no	O
QRS	B-Algorithm
complex	I-Algorithm
following	O
the	O
P	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
If	O
3	O
or	O
more	O
consecutive	O
PACs	O
occur	O
in	O
a	O
row	O
and	O
at	O
a	O
frequency	O
of	O
100	O
or	O
more	O
beats	O
per	O
minute	O
,	O
it	O
may	O
be	O
called	O
atrial	B-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
Premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
are	O
often	O
benign	O
,	O
requiring	O
no	O
treatment	O
.	O
</s>
<s>
Sometimes	O
the	O
PACs	O
can	O
indicate	O
heart	O
disease	O
or	O
an	O
increased	O
risk	O
for	O
other	O
cardiac	B-Application
arrhythmias	I-Application
.	O
</s>
<s>
In	O
otherwise	O
healthy	O
patients	O
,	O
occasional	O
single	O
premature	B-Algorithm
atrial	I-Algorithm
contractions	I-Algorithm
are	O
a	O
common	O
finding	O
and	O
most	O
of	O
times	O
do	O
not	O
indicate	O
any	O
particular	O
health	O
risk	O
.	O
</s>
<s>
Rarely	O
,	O
in	O
patients	O
with	O
other	O
underlying	O
structural	O
heart	O
problems	O
,	O
PACs	O
can	O
trigger	O
a	O
more	O
serious	O
arrhythmia	B-Application
such	O
as	O
atrial	O
flutter	O
or	O
atrial	B-Application
fibrillation	I-Application
.	O
</s>
<s>
A	O
supraventricular	O
extrasystole	B-Algorithm
(	O
SVES	O
)	O
is	O
an	O
extrasystole	B-Algorithm
or	O
premature	O
electrical	O
impulse	O
in	O
the	O
heart	O
,	O
generated	O
above	O
the	O
level	O
of	O
the	O
ventricle	O
.	O
</s>
<s>
This	O
can	O
be	O
either	O
a	O
premature	B-Algorithm
atrial	I-Algorithm
contraction	I-Algorithm
or	O
a	O
premature	O
impulse	O
from	O
the	O
atrioventricular	O
node	O
.	O
</s>
<s>
SVES	O
should	O
be	O
viewed	O
in	O
contrast	O
to	O
a	O
premature	B-Error_Name
ventricular	I-Error_Name
contraction	I-Error_Name
that	O
has	O
a	O
ventricular	O
origin	O
and	O
the	O
associated	O
QRS	B-Algorithm
change	O
.	O
</s>
