<s>
The	O
P	B-Algorithm
wave	I-Algorithm
on	O
the	O
ECG	B-Application
represents	O
atrial	B-Application
depolarization	I-Application
,	O
which	O
results	O
in	O
atrial	O
contraction	O
,	O
or	O
atrial	O
systole	O
.	O
</s>
<s>
The	O
P	B-Algorithm
wave	I-Algorithm
is	O
a	O
summation	O
wave	O
generated	O
by	O
the	O
depolarization	O
front	O
as	O
it	O
transits	O
the	O
atria	O
.	O
</s>
<s>
Depolarization	O
originating	O
elsewhere	O
in	O
the	O
atria	O
(	O
atrial	O
ectopics	O
)	O
result	O
in	O
P	B-Algorithm
waves	I-Algorithm
with	O
a	O
different	O
morphology	O
from	O
normal	O
.	O
</s>
<s>
Peaked	O
P	B-Algorithm
waves	I-Algorithm
(	O
>	O
0.25	O
mV	O
)	O
suggest	O
right	O
atrial	O
enlargement	O
,	O
cor	O
pulmonale	O
,	O
(	O
P	B-Algorithm
pulmonale	I-Algorithm
rhythm	O
)	O
,	O
but	O
have	O
a	O
low	O
predictive	O
value	O
(	O
~	O
20%	O
)	O
.	O
</s>
<s>
A	O
P	B-Algorithm
wave	I-Algorithm
with	O
increased	O
amplitude	O
can	O
indicate	O
hypokalemia	O
.	O
</s>
<s>
A	O
P	B-Algorithm
wave	I-Algorithm
with	O
decreased	O
amplitude	O
can	O
indicate	O
hyperkalemia	O
.	O
</s>
<s>
Bifid	O
P	B-Algorithm
waves	I-Algorithm
(	O
known	O
as	O
P	O
mitrale	O
)	O
indicate	O
left-atrial	O
abnormality	O
-	O
e.g.	O
</s>
<s>
If	O
at	O
least	O
three	O
different	O
shaped	O
P	B-Algorithm
waves	I-Algorithm
can	O
be	O
seen	O
in	O
a	O
given	O
ECG	B-Application
lead	O
tracing	O
,	O
this	O
implies	O
that	O
even	O
if	O
one	O
of	O
them	O
arises	O
from	O
the	O
SA	O
node	O
,	O
at	O
least	O
two	O
others	O
are	O
arising	O
elsewhere	O
.	O
</s>
<s>
at	O
least	O
two	O
)	O
ectopic	B-Algorithm
foci	I-Algorithm
,	O
and	O
is	O
called	O
multifocal	O
(	O
or	O
more	O
correctly	O
,	O
multiform	O
)	O
atrial	O
rhythm	O
if	O
the	O
rate	O
is	O
≤100	O
)	O
or	O
multifocal	B-Algorithm
atrial	I-Algorithm
tachycardia	I-Algorithm
if	O
the	O
rate	O
is	O
over	O
100	O
.	O
</s>
<s>
If	O
the	O
baseline	O
has	O
a	O
totally	O
irregular	O
form	O
,	O
this	O
suggests	O
fibrillatory	O
waves	O
of	O
atrial	B-Application
fibrillation	I-Application
or	O
possibly	O
artefact	O
;	O
a	O
saw	O
tooth	O
shaped	O
baseline	O
suggests	O
the	O
flutter	O
waves	O
of	O
atrial	O
flutter	O
.	O
</s>
<s>
With	O
either	O
of	O
these	O
rhythms	O
,	O
if	O
the	O
ventricular	O
rate	O
is	O
fast	O
,	O
the	O
fibrillatory	O
or	O
flutter	O
waves	O
can	O
easily	O
be	O
misinterpreted	O
as	O
P	B-Algorithm
waves	I-Algorithm
.	O
</s>
<s>
Absence	O
of	O
the	O
P	B-Algorithm
wave	I-Algorithm
with	O
a	O
flat	O
baseline	O
may	O
indicate	O
:	O
</s>
<s>
If	O
P	B-Algorithm
waves	I-Algorithm
are	O
not	O
clearly	O
delineated	O
in	O
the	O
surface	O
ECG	B-Application
,	O
a	O
Lewis	O
lead	O
may	O
be	O
used	O
to	O
better	O
visualize	O
P	B-Algorithm
waves	I-Algorithm
.	O
</s>
<s>
This	O
occurs	O
a	O
mean	O
of	O
320	O
ms	O
after	O
the	O
end	O
of	O
the	O
P	B-Algorithm
wave	I-Algorithm
,	O
with	O
a	O
duration	O
of	O
2-3	O
times	O
that	O
of	O
the	O
P	B-Algorithm
wave	I-Algorithm
and	O
a	O
polarity	O
always	O
opposite	O
to	O
that	O
of	O
the	O
P	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
It	O
is	O
represented	O
on	O
the	O
surface	O
ECG	B-Application
by	O
a	O
so-called	O
Ta	O
wave	O
.	O
</s>
<s>
The	O
clinical	O
relevance	O
of	O
this	O
is	O
that	O
,	O
although	O
a	O
normal	O
phenomenon	O
,	O
the	O
nadir	O
of	O
the	O
Ta	O
wave	O
can	O
occur	O
just	O
after	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
and	O
cause	O
ST	O
depression	O
similar	O
to	O
(	O
and	O
easily	O
mistaken	O
with	O
)	O
that	O
occurring	O
with	O
disease	O
states	O
such	O
as	O
cardiac	O
ischaemia	O
.	O
</s>
