<s>
Signal-averaged	B-Algorithm
electrocardiography	I-Algorithm
(	O
SAECG	B-Algorithm
)	O
is	O
a	O
special	O
electrocardiographic	B-Application
technique	O
,	O
in	O
which	O
multiple	O
electric	O
signals	O
from	O
the	O
heart	O
are	O
averaged	O
to	O
remove	O
interference	O
and	O
reveal	O
small	O
variations	O
in	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
usually	O
the	O
so-called	O
"	O
late	B-Algorithm
potentials	I-Algorithm
"	O
.	O
</s>
<s>
These	O
may	O
represent	O
a	O
predisposition	O
towards	O
potentially	O
dangerous	O
ventricular	B-Application
tachyarrhythmias	I-Application
.	O
</s>
<s>
A	O
resting	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
is	O
recorded	O
in	O
the	O
supine	O
position	O
using	O
an	O
ECG	B-Application
machine	O
equipped	O
with	O
SAECG	B-Algorithm
software	O
;	O
this	O
can	O
be	O
done	O
by	O
a	O
physician	O
,	O
nurse	O
,	O
or	O
medical	O
technician	O
.	O
</s>
<s>
Unlike	O
standard	O
basal	O
ECG	B-Application
recording	O
,	O
which	O
requires	O
only	O
a	O
few	O
seconds	O
,	O
SAECG	B-Algorithm
recording	O
requires	O
a	O
few	O
minutes	O
(	O
usually	O
about	O
7-10	O
minutes	O
)	O
,	O
as	O
the	O
machine	O
must	O
record	O
multiple	O
subsequent	O
QRS	B-Algorithm
potentials	O
to	O
remove	O
interference	O
due	O
to	O
skeletal	O
muscle	O
and	O
to	O
obtain	O
a	O
statistically	B-General_Concept
significant	I-General_Concept
average	O
trace	O
.	O
</s>
<s>
SAECG	B-Algorithm
recording	O
yields	O
a	O
single	O
,	O
averaged	O
QRS	B-Algorithm
potential	O
,	O
usually	O
printed	O
in	O
a	O
much	O
larger	O
scale	O
than	O
standard	O
ECGs	B-Application
,	O
upon	O
which	O
the	O
SAECG	B-Algorithm
software	O
performs	O
calculations	O
to	O
reveal	O
small	O
variations	O
(	O
typically	O
1-25	O
uV	O
)	O
in	O
the	O
final	O
portion	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
(	O
the	O
so-called	O
"	O
late	B-Algorithm
potentials	I-Algorithm
,	O
or	O
more	O
accurately	O
,	O
"	O
late	O
ventricular	O
potentials	O
"	O
)	O
.	O
</s>
<s>
Late	B-Algorithm
potentials	I-Algorithm
are	O
taken	O
to	O
represent	O
delayed	O
and	O
fragmented	O
depolarisation	O
of	O
the	O
ventricular	O
myocardium	O
,	O
which	O
may	O
be	O
the	O
substrate	O
for	O
a	O
micro-re-entry	O
mechanism	O
,	O
implying	O
a	O
higher	O
risk	O
of	O
potentially	O
dangerous	O
ventricular	B-Application
tachyarrhythmias	I-Application
.	O
</s>
<s>
Late	B-Algorithm
potentials	I-Algorithm
may	O
be	O
found	O
in	O
0-10	O
%	O
of	O
normal	O
volunteers	O
.	O
</s>
<s>
When	O
used	O
as	O
a	O
prognostic	O
factor	O
for	O
the	O
development	O
of	O
ventricular	B-Application
tachycardia	I-Application
,	O
they	O
have	O
a	O
sensitivity	O
of	O
72%	O
and	O
a	O
specificity	O
of	O
75%	O
,	O
yielding	O
a	O
positive	O
predictive	O
value	O
of	O
20%	O
and	O
a	O
negative	O
predictive	O
value	O
of	O
20%	O
.	O
</s>
