<s>
Electrical	B-Algorithm
alternans	I-Algorithm
is	O
an	O
electrocardiographic	B-Application
phenomenon	O
of	O
alternation	O
of	O
QRS	B-Algorithm
complex	I-Algorithm
amplitude	O
or	O
axis	O
between	O
beats	O
and	O
a	O
possible	O
wandering	O
base-line	O
.	O
</s>
<s>
The	O
echocardiogram	O
of	O
the	O
heart	O
demonstrated	O
the	O
characteristic	O
swinging	O
along	O
with	O
alternating	O
voltage	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Generally	O
electrical	B-Algorithm
alternans	I-Algorithm
can	O
be	O
seen	O
with	O
tamponade	O
,	O
and	O
narrow	O
AV	O
junctional	O
reentrant	O
tachycardia	B-Application
with	O
an	O
accessory	O
pathway	O
(	O
such	O
as	O
WPW	O
syndrome	O
)	O
.	O
</s>
<s>
A	O
similar	O
phenomenon	O
,	O
pseudo-alternans	O
,	O
can	O
be	O
seen	O
in	O
bigeminal	O
(	O
premature	O
ventricular	O
contraction	O
)	O
PVC	O
in	O
the	O
PR	O
interval	O
,	O
alternans	O
pre-excitation	O
,	O
and	O
alternans	O
bundle	B-Algorithm
branch	I-Algorithm
block	I-Algorithm
.	O
</s>
<s>
Electrical	B-Algorithm
alternans	I-Algorithm
with	O
sinus	B-Algorithm
tachycardia	I-Algorithm
is	O
a	O
highly	O
specific	O
sign	O
for	O
large	O
pericardial	O
effusion	O
.	O
</s>
<s>
This	O
is	O
due	O
to	O
the	O
swinging	O
motion	O
of	O
the	O
heart	O
in	O
the	O
pericardial	O
cavity	O
causing	O
a	O
beat-to-beat	O
variation	O
in	O
QRS	B-Algorithm
axis	O
and	O
amplitude	O
.	O
</s>
