<s>
Changes	O
in	O
the	O
normal	B-Application
ECG	I-Application
pattern	O
occur	O
in	O
numerous	O
cardiac	O
abnormalities	O
,	O
including	O
cardiac	B-Algorithm
rhythm	I-Algorithm
disturbances	O
(	O
such	O
as	O
atrial	B-Application
fibrillation	I-Application
and	O
ventricular	B-Application
tachycardia	I-Application
)	O
,	O
inadequate	O
coronary	O
artery	O
blood	O
flow	O
(	O
such	O
as	O
myocardial	O
ischemia	O
and	O
myocardial	O
infarction	O
)	O
,	O
and	O
electrolyte	O
disturbances	O
(	O
such	O
as	O
hypokalemia	O
and	O
hyperkalemia	O
)	O
.	O
</s>
<s>
Traditionally	O
,	O
"	O
ECG	B-Application
"	O
usually	O
means	O
a	O
12-lead	B-Application
ECG	I-Application
taken	O
while	O
lying	O
down	O
as	O
discussed	O
below	O
.	O
</s>
<s>
However	O
,	O
other	O
devices	O
can	O
record	O
the	O
electrical	O
activity	O
of	O
the	O
heart	O
such	O
as	O
a	O
Holter	O
monitor	O
but	O
also	O
some	O
models	O
of	O
smartwatch	B-Application
are	O
capable	O
of	O
recording	O
an	O
ECG	B-Application
.	O
</s>
<s>
ECG	B-Application
signals	O
can	O
be	O
recorded	O
in	O
other	O
contexts	O
with	O
other	O
devices	O
.	O
</s>
<s>
In	O
a	O
conventional	O
12-lead	B-Application
ECG	I-Application
,	O
ten	O
electrodes	O
are	O
placed	O
on	O
the	O
patient	O
's	O
limbs	O
and	O
on	O
the	O
surface	O
of	O
the	O
chest	O
.	O
</s>
<s>
There	O
are	O
three	O
main	O
components	O
to	O
an	O
ECG	B-Application
:	O
the	O
P	B-Algorithm
wave	I-Algorithm
,	O
which	O
represents	O
depolarization	O
of	O
the	O
atria	O
;	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
which	O
represents	O
depolarization	O
of	O
the	O
ventricles	O
;	O
and	O
the	O
T	B-Algorithm
wave	I-Algorithm
,	O
which	O
represents	O
repolarization	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
During	O
each	O
heartbeat	O
,	O
a	O
healthy	O
heart	O
has	O
an	O
orderly	O
progression	O
of	O
depolarization	O
that	O
starts	O
with	O
pacemaker	B-Algorithm
cells	I-Algorithm
in	O
the	O
sinoatrial	O
node	O
,	O
spreads	O
throughout	O
the	O
atrium	O
,	O
and	O
passes	O
through	O
the	O
atrioventricular	B-Algorithm
node	O
down	O
into	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
and	O
into	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
,	O
spreading	O
down	O
and	O
to	O
the	O
left	O
throughout	O
the	O
ventricles	O
.	O
</s>
<s>
This	O
orderly	O
pattern	O
of	O
depolarization	O
gives	O
rise	O
to	O
the	O
characteristic	O
ECG	B-Application
tracing	O
.	O
</s>
<s>
To	O
the	O
trained	O
clinician	O
,	O
an	O
ECG	B-Application
conveys	O
a	O
large	O
amount	O
of	O
information	O
about	O
the	O
structure	O
of	O
the	O
heart	O
and	O
the	O
function	O
of	O
its	O
electrical	O
conduction	B-Algorithm
system	I-Algorithm
.	O
</s>
<s>
Among	O
other	O
things	O
,	O
an	O
ECG	B-Application
can	O
be	O
used	O
to	O
measure	O
the	O
rate	O
and	O
rhythm	O
of	O
heartbeats	O
,	O
the	O
size	O
and	O
position	O
of	O
the	O
heart	O
chambers	O
,	O
the	O
presence	O
of	O
any	O
damage	O
to	O
the	O
heart	O
's	O
muscle	O
cells	O
or	O
conduction	B-Algorithm
system	I-Algorithm
,	O
the	O
effects	O
of	O
heart	O
drugs	O
,	O
and	O
the	O
function	O
of	O
implanted	B-Device
pacemakers	I-Device
.	O
</s>
<s>
The	O
overall	O
goal	O
of	O
performing	O
an	O
ECG	B-Application
is	O
to	O
obtain	O
information	O
about	O
the	O
electrical	O
functioning	O
of	O
the	O
heart	O
.	O
</s>
<s>
Some	O
indications	O
for	O
performing	O
an	O
ECG	B-Application
include	O
the	O
following	O
:	O
</s>
<s>
Clinical	B-Algorithm
cardiac	I-Algorithm
electrophysiology	I-Algorithm
,	O
in	O
which	O
a	O
catheter	O
is	O
inserted	O
through	O
the	O
femoral	O
vein	O
and	O
can	O
have	O
several	O
electrodes	O
along	O
its	O
length	O
to	O
record	O
the	O
direction	O
of	O
electrical	O
activity	O
from	O
within	O
the	O
heart	O
.	O
</s>
<s>
ECGs	B-Application
can	O
be	O
recorded	O
as	O
short	O
intermittent	O
tracings	O
or	O
continuous	O
ECG	B-Application
monitoring	O
.	O
</s>
<s>
Continuous	O
monitoring	O
is	O
used	O
for	O
critically	O
ill	O
patients	O
,	O
patients	O
undergoing	O
general	O
anesthesia	O
,	O
and	O
patients	O
who	O
have	O
an	O
infrequently	O
occurring	O
cardiac	B-Application
arrhythmia	I-Application
that	O
would	O
unlikely	O
be	O
seen	O
on	O
a	O
conventional	O
ten-second	O
ECG	B-Application
.	O
</s>
<s>
Continuous	O
monitoring	O
can	O
be	O
conducted	O
by	O
using	O
Holter	O
monitors	O
,	O
internal	O
and	O
external	O
defibrillators	O
and	O
pacemakers	B-Device
,	O
and/or	O
biotelemetry	O
.	O
</s>
<s>
For	O
adults	O
,	O
evidence	O
does	O
not	O
support	O
the	O
use	O
of	O
ECGs	B-Application
among	O
those	O
without	O
symptoms	O
or	O
at	O
low	O
risk	O
of	O
cardiovascular	O
disease	O
as	O
an	O
effort	O
for	O
prevention	O
.	O
</s>
<s>
This	O
is	O
because	O
an	O
ECG	B-Application
may	O
falsely	O
indicate	O
the	O
existence	O
of	O
a	O
problem	O
,	O
leading	O
to	O
misdiagnosis	O
,	O
the	O
recommendation	O
of	O
invasive	O
procedures	O
,	O
and	O
overtreatment	O
.	O
</s>
<s>
However	O
,	O
persons	O
employed	O
in	O
certain	O
critical	O
occupations	O
,	O
such	O
as	O
aircraft	O
pilots	O
,	O
may	O
be	O
required	O
to	O
have	O
an	O
ECG	B-Application
as	O
part	O
of	O
their	O
routine	O
health	O
evaluations	O
.	O
</s>
<s>
Electrocardiograms	B-Application
are	O
recorded	O
by	O
machines	O
that	O
consist	O
of	O
a	O
set	O
of	O
electrodes	O
connected	O
to	O
a	O
central	O
unit	O
.	O
</s>
<s>
Early	O
ECG	B-Application
machines	O
were	O
constructed	O
with	O
analog	O
electronics	O
,	O
where	O
the	O
signal	O
drove	O
a	O
motor	O
to	O
print	O
out	O
the	O
signal	O
onto	O
paper	O
.	O
</s>
<s>
Today	O
,	O
electrocardiographs	B-Application
use	O
analog-to-digital	O
converters	O
to	O
convert	O
the	O
electrical	O
activity	O
of	O
the	O
heart	O
to	O
a	O
digital	O
signal	O
.	O
</s>
<s>
Many	O
ECG	B-Application
machines	O
are	O
now	O
portable	O
and	O
commonly	O
include	O
a	O
screen	O
,	O
keyboard	O
,	O
and	O
printer	O
on	O
a	O
small	O
wheeled	O
cart	O
.	O
</s>
<s>
Recent	O
advancements	O
in	O
electrocardiography	B-Application
include	O
developing	O
even	O
smaller	O
devices	O
for	O
inclusion	O
in	O
fitness	O
trackers	O
and	O
smart	B-Application
watches	I-Application
.	O
</s>
<s>
Recording	O
an	O
ECG	B-Application
is	O
a	O
safe	O
and	O
painless	O
procedure	O
.	O
</s>
<s>
Defibrillation	O
protection	O
:	O
any	O
ECG	B-Application
used	O
in	O
healthcare	O
may	O
be	O
attached	O
to	O
a	O
person	O
who	O
requires	O
defibrillation	O
and	O
the	O
ECG	B-Application
needs	O
to	O
protect	O
itself	O
from	O
this	O
source	O
of	O
energy	O
.	O
</s>
<s>
ECG	B-Application
voltages	O
measured	O
across	O
the	O
body	O
are	O
very	O
small	O
.	O
</s>
<s>
Most	O
modern	O
ECG	B-Application
machines	O
include	O
automated	O
interpretation	O
algorithms	O
.	O
</s>
<s>
This	O
analysis	O
calculates	O
features	O
such	O
as	O
the	O
PR	B-Algorithm
interval	I-Algorithm
,	O
QT	B-Algorithm
interval	I-Algorithm
,	O
corrected	O
QT	O
(	O
QTc	B-Algorithm
)	O
interval	O
,	O
PR	O
axis	O
,	O
QRS	B-Algorithm
axis	O
,	O
rhythm	O
and	O
more	O
.	O
</s>
<s>
Besides	O
the	O
standard	O
electrocardiograph	B-Application
machine	O
,	O
there	O
are	O
other	O
devices	O
capable	O
of	O
recording	O
ECG	B-Application
signals	O
.	O
</s>
<s>
Traditionally	O
,	O
these	O
monitors	O
have	O
used	O
electrodes	O
with	O
patches	O
on	O
the	O
skin	O
to	O
record	O
the	O
ECG	B-Application
,	O
but	O
new	O
devices	O
can	O
stick	O
to	O
the	O
chest	O
as	O
a	O
single	O
patch	O
without	O
need	O
for	O
wires	O
,	O
developed	O
by	O
Zio	O
(	O
Zio	O
XT	O
)	O
,	O
TZ	O
Medical	O
(	O
Trident	O
)	O
,	O
Philips	O
(	O
BioTel	O
)	O
and	O
BardyDx	O
(	O
CAM	O
)	O
among	O
many	O
others	O
.	O
</s>
<s>
Implantable	O
devices	O
such	O
as	O
the	O
artificial	B-Device
cardiac	I-Device
pacemaker	I-Device
and	O
implantable	O
cardioverter-defibrillator	O
are	O
capable	O
of	O
measuring	O
a	O
"	O
far	O
field	O
"	O
signal	O
between	O
the	O
leads	O
in	O
the	O
heart	O
and	O
the	O
implanted	O
battery/generator	O
that	O
resembles	O
an	O
ECG	B-Application
signal	O
(	O
technically	O
,	O
the	O
signal	O
recorded	O
in	O
the	O
heart	O
is	O
called	O
an	O
electrogram	O
,	O
which	O
is	O
interpreted	O
differently	O
)	O
.	O
</s>
<s>
Additionally	O
,	O
there	O
are	O
available	O
various	O
Arduino	O
kits	O
with	O
ECG	B-Application
sensor	O
modules	O
and	O
smartwatch	B-Application
devices	O
that	O
are	O
capable	O
of	O
recording	O
an	O
ECG	B-Application
signal	O
as	O
well	O
,	O
such	O
as	O
with	O
the	O
4th	O
generation	O
Apple	B-Device
Watch	I-Device
,	O
Samsung	B-Application
Galaxy	I-Application
Watch	I-Application
4	I-Application
and	O
newer	O
devices	O
.	O
</s>
<s>
Commonly	O
,	O
10	O
electrodes	O
attached	O
to	O
the	O
body	O
are	O
used	O
to	O
form	O
12	O
ECG	B-Application
leads	O
,	O
with	O
each	O
lead	O
measuring	O
a	O
specific	O
electrical	O
potential	O
difference	O
(	O
as	O
listed	O
in	O
the	O
table	O
below	O
)	O
.	O
</s>
<s>
The	O
12-lead	B-Application
ECG	I-Application
has	O
a	O
total	O
of	O
three	O
limb	O
leads	O
and	O
three	O
augmented	O
limb	O
leads	O
arranged	O
like	O
spokes	O
of	O
a	O
wheel	O
in	O
the	O
coronal	O
plane	O
(	O
vertical	O
)	O
,	O
and	O
six	O
precordial	O
leads	O
or	O
chest	O
leads	O
that	O
lie	O
on	O
the	O
perpendicular	O
transverse	O
plane	O
(	O
horizontal	O
)	O
.	O
</s>
<s>
The	O
10	O
electrodes	O
in	O
a	O
12-lead	B-Application
ECG	I-Application
are	O
listed	O
below	O
.	O
</s>
<s>
The	O
former	O
are	O
typically	O
used	O
in	O
a	O
single	O
ECG	B-Application
recording	O
while	O
the	O
latter	O
are	O
for	O
continuous	O
recordings	O
as	O
they	O
stick	O
longer	O
.	O
</s>
<s>
The	O
gel	O
typically	O
contains	O
potassium	O
chloride	O
–	O
sometimes	O
silver	O
chloride	O
as	O
well	O
–	O
to	O
permit	O
electron	O
conduction	B-Algorithm
from	O
the	O
skin	O
to	O
the	O
wire	O
and	O
to	O
the	O
electrocardiogram	B-Application
.	O
</s>
<s>
In	O
a	O
12-lead	B-Application
ECG	I-Application
,	O
all	O
leads	O
except	O
the	O
limb	O
leads	O
are	O
assumed	O
to	O
be	O
unipolar	O
(	O
aVR	O
,	O
aVL	O
,	O
aVF	O
,	O
V1	O
,	O
V2	O
,	O
V3	O
,	O
V4	O
,	O
V5	O
,	O
and	O
V6	O
)	O
.	O
</s>
<s>
Together	O
with	O
leads	O
I	O
,	O
II	O
,	O
and	O
III	O
,	O
augmented	O
limb	O
leads	O
aVR	O
,	O
aVL	O
,	O
and	O
aVF	O
form	O
the	O
basis	O
of	O
the	O
hexaxial	B-Algorithm
reference	I-Algorithm
system	I-Algorithm
,	O
which	O
is	O
used	O
to	O
calculate	O
the	O
heart	O
's	O
electrical	O
axis	O
in	O
the	O
frontal	O
plane	O
.	O
</s>
<s>
Older	O
versions	O
of	O
the	O
nodes	O
(	O
VR	O
,	O
VL	O
,	O
VF	O
)	O
use	O
Wilson	O
's	O
central	O
terminal	O
as	O
the	O
negative	O
pole	O
,	O
but	O
the	O
amplitude	O
is	O
too	O
small	O
for	O
the	O
thick	O
lines	O
of	O
old	O
ECG	B-Application
machines	O
.	O
</s>
<s>
An	O
esophageal	O
lead	O
avails	O
for	O
a	O
more	O
accurate	O
differentiation	O
between	O
certain	O
cardiac	B-Application
arrhythmias	I-Application
,	O
particularly	O
atrial	O
flutter	O
,	O
AV	B-Algorithm
nodal	I-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
and	O
orthodromic	O
atrioventricular	B-Algorithm
reentrant	I-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
It	O
can	O
also	O
evaluate	O
the	O
risk	O
in	O
people	O
with	O
Wolff-Parkinson-White	O
syndrome	O
,	O
as	O
well	O
as	O
terminate	O
supraventricular	B-Algorithm
tachycardia	I-Algorithm
caused	O
by	O
re-entry	O
.	O
</s>
<s>
An	O
intracardiac	B-Application
electrogram	I-Application
(	O
ICEG	O
)	O
is	O
essentially	O
an	O
ECG	B-Application
with	O
some	O
added	O
intracardiac	O
leads	O
(	O
that	O
is	O
,	O
inside	O
the	O
heart	O
)	O
.	O
</s>
<s>
The	O
standard	O
ECG	B-Application
leads	O
(	O
external	O
leads	O
)	O
are	O
I	O
,	O
II	O
,	O
III	O
,	O
aVL	O
,	O
V1	O
,	O
and	O
V6	O
.	O
</s>
<s>
The	O
word	O
"	O
electrogram	O
"	O
(	O
EGM	O
)	O
without	O
further	O
specification	O
usually	O
means	O
an	O
intracardiac	B-Application
electrogram	I-Application
.	O
</s>
<s>
A	O
standard	O
12-lead	B-Application
ECG	I-Application
report	O
(	O
an	O
electrocardiograph	B-Application
)	O
shows	O
a	O
2.5	O
second	O
tracing	O
of	O
each	O
of	O
the	O
twelve	O
leads	O
.	O
</s>
<s>
The	O
timing	O
across	O
the	O
page	O
is	O
continuous	O
and	O
notes	O
tracings	O
of	O
the	O
12	B-Application
leads	I-Application
for	O
the	O
same	O
time	O
period	O
.	O
</s>
<s>
Each	O
of	O
the	O
12	O
ECG	B-Application
leads	O
records	O
the	O
electrical	O
activity	O
of	O
the	O
heart	O
from	O
a	O
different	O
angle	O
,	O
and	O
therefore	O
align	O
with	O
different	O
anatomical	O
areas	O
of	O
the	O
heart	O
.	O
</s>
<s>
The	O
study	O
of	O
the	O
conduction	B-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
is	O
called	O
cardiac	B-Algorithm
electrophysiology	I-Algorithm
(	O
EP	O
)	O
.	O
</s>
<s>
An	O
EP	O
study	O
is	O
performed	O
via	O
a	O
right-sided	O
cardiac	O
catheterization	O
:	O
a	O
wire	O
with	O
an	O
electrode	O
at	O
its	O
tip	O
is	O
inserted	O
into	O
the	O
right	O
heart	O
chambers	O
from	O
a	O
peripheral	O
vein	O
,	O
and	O
placed	O
in	O
various	O
positions	O
in	O
close	O
proximity	O
to	O
the	O
conduction	B-Algorithm
system	I-Algorithm
so	O
that	O
the	O
electrical	O
activity	O
of	O
that	O
system	O
can	O
be	O
recorded	O
.	O
</s>
<s>
Standard	O
catheter	O
positions	O
for	O
an	O
EP	O
study	O
include	O
"	O
high	O
right	O
atrium	O
"	O
or	O
hRA	O
near	O
the	O
sinus	O
node	O
,	O
a	O
"	O
His	O
"	O
across	O
the	O
septal	O
wall	O
of	O
the	O
tricuspid	O
valve	O
to	O
measure	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
a	O
"	O
coronary	O
sinus	O
"	O
into	O
the	O
coronary	O
sinus	O
,	O
and	O
a	O
"	O
right	O
ventricle	O
"	O
in	O
the	O
apex	O
of	O
the	O
right	O
ventricle	O
.	O
</s>
<s>
Interpretation	O
of	O
the	O
ECG	B-Application
is	O
fundamentally	O
about	O
understanding	O
the	O
electrical	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
of	I-Algorithm
the	I-Algorithm
heart	I-Algorithm
.	O
</s>
<s>
Normal	O
conduction	B-Algorithm
starts	O
and	O
propagates	O
in	O
a	O
predictable	O
pattern	O
,	O
and	O
deviation	O
from	O
this	O
pattern	O
can	O
be	O
a	O
normal	O
variation	O
or	O
be	O
pathological	O
.	O
</s>
<s>
An	O
ECG	B-Application
does	O
not	O
equate	O
with	O
mechanical	O
pumping	O
activity	O
of	O
the	O
heart	O
,	O
for	O
example	O
,	O
pulseless	O
electrical	O
activity	O
produces	O
an	O
ECG	B-Application
that	O
should	O
pump	O
blood	O
but	O
no	O
pulses	O
are	O
felt	O
(	O
and	O
constitutes	O
a	O
medical	O
emergency	O
and	O
CPR	O
should	O
be	O
performed	O
)	O
.	O
</s>
<s>
Ventricular	O
fibrillation	O
produces	O
an	O
ECG	B-Application
but	O
is	O
too	O
dysfunctional	O
to	O
produce	O
a	O
life-sustaining	O
cardiac	O
output	O
.	O
</s>
<s>
Ultimately	O
,	O
an	O
echocardiogram	B-Application
or	O
other	O
anatomical	O
imaging	O
modality	O
is	O
useful	O
in	O
assessing	O
the	O
mechanical	O
function	O
of	O
the	O
heart	O
.	O
</s>
<s>
Interpretation	O
of	O
the	O
ECG	B-Application
is	O
ultimately	O
that	O
of	O
pattern	O
recognition	O
.	O
</s>
<s>
In	O
order	O
to	O
understand	O
the	O
patterns	O
found	O
,	O
it	O
is	O
helpful	O
to	O
understand	O
the	O
theory	O
of	O
what	O
ECGs	B-Application
represent	O
.	O
</s>
<s>
Normal	O
rhythm	O
produces	O
four	O
entities	O
–	O
a	O
P	B-Algorithm
wave	I-Algorithm
,	O
a	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
a	O
T	B-Algorithm
wave	I-Algorithm
,	O
and	O
a	O
U	B-Algorithm
wave	I-Algorithm
–	O
that	O
each	O
have	O
a	O
fairly	O
unique	O
pattern	O
.	O
</s>
<s>
The	O
P	B-Algorithm
wave	I-Algorithm
represents	O
atrial	B-Application
depolarization	I-Application
.	O
</s>
<s>
The	O
QRS	B-Algorithm
complex	I-Algorithm
represents	O
ventricular	B-Application
depolarization	I-Application
.	O
</s>
<s>
The	O
T	B-Algorithm
wave	I-Algorithm
represents	O
ventricular	B-Application
repolarization	I-Application
.	O
</s>
<s>
The	O
U	B-Algorithm
wave	I-Algorithm
represents	O
papillary	O
muscle	O
repolarization	O
.	O
</s>
<s>
The	O
U	B-Algorithm
wave	I-Algorithm
is	O
not	O
typically	O
seen	O
and	O
its	O
absence	O
is	O
generally	O
ignored	O
.	O
</s>
<s>
Atrial	O
repolarisation	O
is	O
typically	O
hidden	O
in	O
the	O
much	O
more	O
prominent	O
QRS	B-Algorithm
complex	I-Algorithm
and	O
normally	O
cannot	O
be	O
seen	O
without	O
additional	O
,	O
specialised	O
electrodes	O
.	O
</s>
<s>
ECGs	B-Application
are	O
normally	O
printed	O
on	O
a	O
grid	O
.	O
</s>
<s>
Faster	O
speeds	O
such	O
as	O
100	O
and	O
200mm	O
per	O
sec	O
are	O
used	O
during	O
electrophysiology	B-Algorithm
studies	O
.	O
</s>
<s>
Not	O
all	O
aspects	O
of	O
an	O
ECG	B-Application
rely	O
on	O
precise	O
recordings	O
or	O
having	O
a	O
known	O
scaling	O
of	O
amplitude	O
or	O
time	O
.	O
</s>
<s>
A	O
heart	O
rate	O
below	O
normal	O
is	O
called	O
"	O
bradycardia	B-Algorithm
"	O
(	O
<	O
60	O
in	O
adults	O
)	O
and	O
above	O
normal	O
is	O
called	O
"	O
tachycardia	B-Application
"	O
(	O
>100	O
in	O
adults	O
)	O
.	O
</s>
<s>
Normal	O
sinus	O
rhythm	O
produces	O
the	O
prototypical	O
pattern	O
of	O
P	B-Algorithm
wave	I-Algorithm
,	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
and	O
T	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
Generally	O
,	O
deviation	O
from	O
normal	O
sinus	O
rhythm	O
is	O
considered	O
a	O
cardiac	B-Application
arrhythmia	I-Application
.	O
</s>
<s>
Thus	O
,	O
the	O
first	O
question	O
in	O
interpreting	O
an	O
ECG	B-Application
is	O
whether	O
or	O
not	O
there	O
is	O
a	O
sinus	O
rhythm	O
.	O
</s>
<s>
A	O
criterion	O
for	O
sinus	O
rhythm	O
is	O
that	O
P	B-Algorithm
waves	I-Algorithm
and	O
QRS	B-Algorithm
complexes	I-Algorithm
appear	O
1-to-1	O
,	O
thus	O
implying	O
that	O
the	O
P	B-Algorithm
wave	I-Algorithm
causes	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
For	O
a	O
sinus	O
rhythm	O
,	O
this	O
is	O
either	O
the	O
rate	O
of	O
P	B-Algorithm
waves	I-Algorithm
or	O
QRS	B-Algorithm
complexes	I-Algorithm
since	O
they	O
are	O
1-to-1	O
.	O
</s>
<s>
If	O
the	O
rate	O
is	O
too	O
fast	O
,	O
then	O
it	O
is	O
sinus	B-Algorithm
tachycardia	I-Algorithm
,	O
and	O
if	O
it	O
is	O
too	O
slow	O
,	O
then	O
it	O
is	O
sinus	B-Algorithm
bradycardia	I-Algorithm
.	O
</s>
<s>
Some	O
arrhythmias	B-Application
with	O
characteristic	O
findings	O
:	O
</s>
<s>
Absent	O
P	B-Algorithm
waves	I-Algorithm
with	O
"	O
irregularly	O
irregular	O
"	O
QRS	B-Algorithm
complexes	I-Algorithm
is	O
the	O
hallmark	O
of	O
atrial	B-Application
fibrillation	I-Application
.	O
</s>
<s>
A	O
"	O
saw	O
tooth	O
"	O
pattern	O
with	O
QRS	B-Algorithm
complexes	I-Algorithm
is	O
the	O
hallmark	O
of	O
atrial	O
flutter	O
.	O
</s>
<s>
A	O
sine	O
wave	O
pattern	O
is	O
the	O
hallmark	O
of	O
ventricular	B-Algorithm
flutter	I-Algorithm
.	O
</s>
<s>
Absent	O
P	B-Algorithm
waves	I-Algorithm
with	O
wide	O
QRS	B-Algorithm
complexes	I-Algorithm
and	O
a	O
fast	B-Application
heart	I-Application
rate	I-Application
is	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
The	O
heart	O
has	O
several	O
axes	O
,	O
but	O
the	O
most	O
common	O
by	O
far	O
is	O
the	O
axis	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
(	O
references	O
to	O
"	O
the	O
axis	O
"	O
imply	O
the	O
QRS	B-Algorithm
axis	O
)	O
.	O
</s>
<s>
The	O
QRS	B-Algorithm
axis	O
is	O
the	O
general	O
direction	O
of	O
the	O
ventricular	B-Application
depolarization	I-Application
wavefront	O
(	O
or	O
mean	O
electrical	O
vector	O
)	O
in	O
the	O
frontal	O
plane	O
.	O
</s>
<s>
Population	O
data	O
shows	O
that	O
a	O
normal	O
QRS	B-Algorithm
axis	O
is	O
from	O
−30°	O
to	O
105°	O
,	O
with	O
0°	O
being	O
along	O
lead	O
I	O
and	O
positive	O
being	O
inferior	O
and	O
negative	O
being	O
superior	O
(	O
best	O
understood	O
graphically	O
as	O
the	O
hexaxial	B-Algorithm
reference	I-Algorithm
system	I-Algorithm
)	O
.	O
</s>
<s>
A	O
shortcut	O
for	O
determining	O
if	O
the	O
QRS	B-Algorithm
axis	O
is	O
normal	O
is	O
if	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
is	O
mostly	O
positive	O
in	O
lead	O
I	O
and	O
lead	O
II	O
(	O
or	O
lead	O
I	O
and	O
aVF	O
if	O
+90°	O
is	O
the	O
upper	O
limit	O
of	O
normal	O
)	O
.	O
</s>
<s>
The	O
normal	O
QRS	B-Algorithm
axis	O
is	O
generally	O
down	O
and	O
to	O
the	O
left	O
,	O
following	O
the	O
anatomical	O
orientation	O
of	O
the	O
heart	O
within	O
the	O
chest	O
.	O
</s>
<s>
An	O
abnormal	O
axis	O
suggests	O
a	O
change	O
in	O
the	O
physical	O
shape	O
and	O
orientation	O
of	O
the	O
heart	O
or	O
a	O
defect	O
in	O
its	O
conduction	B-Algorithm
system	I-Algorithm
that	O
causes	O
the	O
ventricles	O
to	O
depolarize	O
in	O
an	O
abnormal	O
way	O
.	O
</s>
<s>
All	O
of	O
the	O
waves	O
on	O
an	O
ECG	B-Application
tracing	O
and	O
the	O
intervals	O
between	O
them	O
have	O
a	O
predictable	O
time	O
duration	O
,	O
a	O
range	O
of	O
acceptable	O
amplitudes	O
(	O
voltages	O
)	O
,	O
and	O
a	O
typical	O
morphology	O
.	O
</s>
<s>
For	O
ease	O
of	O
measuring	O
the	O
amplitudes	O
and	O
intervals	O
,	O
an	O
ECG	B-Application
is	O
printed	O
on	O
graph	O
paper	O
at	O
a	O
standard	O
scale	O
:	O
each	O
1mm	O
(	O
one	O
small	O
box	O
on	O
the	O
standard	O
25mm/s	O
ECG	B-Application
paper	O
)	O
represents	O
40	O
milliseconds	O
of	O
time	O
on	O
the	O
x-axis	O
,	O
and	O
0.1	O
millivolts	O
on	O
the	O
y-axis	O
.	O
</s>
<s>
FeatureDescriptionPathologyDurationP	O
waveThe	O
P	B-Algorithm
wave	I-Algorithm
represents	O
depolarization	O
of	O
the	O
atria	O
.	O
</s>
<s>
Atrial	B-Application
depolarization	I-Application
spreads	O
from	O
the	O
SA	O
node	O
towards	O
the	O
AV	O
node	O
,	O
and	O
from	O
the	O
right	O
atrium	O
to	O
the	O
left	O
atrium.The	O
P	B-Algorithm
wave	I-Algorithm
is	O
typically	O
upright	O
in	O
most	O
leads	O
except	O
for	O
aVR	O
;	O
an	O
unusual	O
P	B-Algorithm
wave	I-Algorithm
axis	O
(	O
inverted	O
in	O
other	O
leads	O
)	O
can	O
indicate	O
an	O
ectopic	B-Algorithm
atrial	I-Algorithm
pacemaker	I-Algorithm
.	O
</s>
<s>
If	O
the	O
P	B-Algorithm
wave	I-Algorithm
is	O
of	O
unusually	O
long	O
duration	O
,	O
it	O
may	O
represent	O
atrial	O
enlargement	O
.	O
</s>
<s>
Typically	O
a	O
large	O
right	O
atrium	O
gives	O
a	O
tall	O
,	O
peaked	O
P	B-Algorithm
wave	I-Algorithm
while	O
a	O
large	O
left	O
atrium	O
gives	O
a	O
two-humped	O
bifid	O
P	O
wave.	O
<	O
80	O
msPR	O
intervalThe	O
PR	B-Algorithm
interval	I-Algorithm
is	O
measured	O
from	O
the	O
beginning	O
of	O
the	O
P	B-Algorithm
wave	I-Algorithm
to	O
the	O
beginning	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
This	O
interval	O
reflects	O
the	O
time	O
the	O
electrical	O
impulse	O
takes	O
to	O
travel	O
from	O
the	O
sinus	O
node	O
through	O
the	O
AV	O
node.A	O
PR	B-Algorithm
interval	I-Algorithm
shorter	O
than	O
120	O
ms	O
suggests	O
that	O
the	O
electrical	O
impulse	O
is	O
bypassing	O
the	O
AV	O
node	O
,	O
as	O
in	O
Wolf-Parkinson-White	O
syndrome	O
.	O
</s>
<s>
A	O
PR	B-Algorithm
interval	I-Algorithm
consistently	O
longer	O
than	O
200	O
ms	O
diagnoses	O
first	B-Algorithm
degree	I-Algorithm
atrioventricular	I-Algorithm
block	I-Algorithm
.	O
</s>
<s>
The	O
PR	O
segment	O
(	O
the	O
portion	O
of	O
the	O
tracing	O
after	O
the	O
P	B-Algorithm
wave	I-Algorithm
and	O
before	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
)	O
is	O
typically	O
completely	O
flat	O
,	O
but	O
may	O
be	O
depressed	O
in	O
pericarditis.120	O
to	O
200	O
msQRS	O
complexThe	O
QRS	B-Algorithm
complex	I-Algorithm
represents	O
the	O
rapid	O
depolarization	O
of	O
the	O
right	O
and	O
left	O
ventricles	O
.	O
</s>
<s>
The	O
ventricles	O
have	O
a	O
large	O
muscle	O
mass	O
compared	O
to	O
the	O
atria	O
,	O
so	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
usually	O
has	O
a	O
much	O
larger	O
amplitude	O
than	O
the	O
P	O
wave.If	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
is	O
wide	O
(	O
longer	O
than	O
120	O
ms	O
)	O
it	O
suggests	O
disruption	O
of	O
the	O
heart	O
's	O
conduction	B-Algorithm
system	I-Algorithm
,	O
such	O
as	O
in	O
LBBB	O
,	O
RBBB	B-Algorithm
,	O
or	O
ventricular	O
rhythms	O
such	O
as	O
ventricular	B-Application
tachycardia	I-Application
.	O
</s>
<s>
Metabolic	O
issues	O
such	O
as	O
severe	O
hyperkalemia	O
,	O
or	O
tricyclic	O
antidepressant	O
overdose	O
can	O
also	O
widen	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
An	O
unusually	O
tall	O
QRS	B-Algorithm
complex	I-Algorithm
may	O
represent	O
left	O
ventricular	O
hypertrophy	O
while	O
a	O
very	O
low-amplitude	O
QRS	B-Algorithm
complex	I-Algorithm
may	O
represent	O
a	O
pericardial	O
effusion	O
or	O
infiltrative	O
myocardial	O
disease.80	O
to	O
100	O
msJ-pointThe	O
J-point	O
is	O
the	O
point	O
at	O
which	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
finishes	O
and	O
the	O
ST	B-Algorithm
segment	I-Algorithm
begins.The	O
J-point	O
may	O
be	O
elevated	O
as	O
a	O
normal	O
variant	O
.	O
</s>
<s>
The	O
appearance	O
of	O
a	O
separate	O
J	B-Algorithm
wave	I-Algorithm
or	O
Osborn	B-Algorithm
wave	I-Algorithm
at	O
the	O
J-point	O
is	O
pathognomonic	O
of	O
hypothermia	O
or	O
hypercalcemia.ST	O
segmentThe	O
ST	B-Algorithm
segment	I-Algorithm
connects	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
and	O
the	O
T	B-Algorithm
wave	I-Algorithm
;	O
it	O
represents	O
the	O
period	O
when	O
the	O
ventricles	O
are	O
depolarized.It	O
is	O
usually	O
isoelectric	O
,	O
but	O
may	O
be	O
depressed	O
or	O
elevated	O
with	O
myocardial	O
infarction	O
or	O
ischemia	O
.	O
</s>
<s>
ST	B-Algorithm
depression	I-Algorithm
can	O
also	O
be	O
caused	O
by	O
LVH	O
or	O
digoxin	O
.	O
</s>
<s>
ST	B-Algorithm
elevation	I-Algorithm
can	O
also	O
be	O
caused	O
by	O
pericarditis	O
,	O
Brugada	O
syndrome	O
,	O
or	O
can	O
be	O
a	O
normal	O
variant	O
(	O
J-point	O
elevation	O
)	O
.T	O
waveThe	O
T	B-Algorithm
wave	I-Algorithm
represents	O
the	O
repolarization	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
It	O
is	O
generally	O
upright	O
in	O
all	O
leads	O
except	O
aVR	O
and	O
lead	O
V1.Inverted	O
T	B-Algorithm
waves	I-Algorithm
can	O
be	O
a	O
sign	O
of	O
myocardial	O
ischemia	O
,	O
left	O
ventricular	O
hypertrophy	O
,	O
high	O
intracranial	O
pressure	O
,	O
or	O
metabolic	O
abnormalities	O
.	O
</s>
<s>
Peaked	O
T	B-Algorithm
waves	I-Algorithm
can	O
be	O
a	O
sign	O
of	O
hyperkalemia	O
or	O
very	O
early	O
myocardial	O
infarction.160	O
msCorrected	O
QT	B-Algorithm
interval	I-Algorithm
(	O
QTc	B-Algorithm
)	O
The	O
QT	B-Algorithm
interval	I-Algorithm
is	O
measured	O
from	O
the	O
beginning	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
to	O
the	O
end	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
Acceptable	O
ranges	O
vary	O
with	O
heart	O
rate	O
,	O
so	O
it	O
must	O
be	O
corrected	O
to	O
the	O
QTc	B-Algorithm
by	O
dividing	O
by	O
the	O
square	O
root	O
of	O
the	O
RR	O
interval.A	O
prolonged	O
QTc	B-Algorithm
interval	O
is	O
a	O
risk	O
factor	O
for	O
ventricular	B-Application
tachyarrhythmias	I-Application
and	O
sudden	O
death	O
.	O
</s>
<s>
An	O
unusually	O
short	O
QTc	B-Algorithm
can	O
be	O
seen	O
in	O
severe	O
hypercalcemia.	O
<	O
440	O
msU	O
waveThe	O
U	B-Algorithm
wave	I-Algorithm
is	O
hypothesized	O
to	O
be	O
caused	O
by	O
the	O
repolarization	O
of	O
the	O
interventricular	O
septum	O
.	O
</s>
<s>
It	O
normally	O
has	O
a	O
low	O
amplitude	O
,	O
and	O
even	O
more	O
often	O
is	O
completely	O
absent.A	O
very	O
prominent	O
U	B-Algorithm
wave	I-Algorithm
can	O
be	O
a	O
sign	O
of	O
hypokalemia	O
,	O
hypercalcemia	O
or	O
hyperthyroidism	O
.	O
</s>
<s>
The	O
animation	O
shown	O
to	O
the	O
right	O
illustrates	O
how	O
the	O
path	O
of	O
electrical	O
conduction	B-Algorithm
gives	O
rise	O
to	O
the	O
ECG	B-Application
waves	O
in	O
the	O
limb	O
leads	O
.	O
</s>
<s>
Recall	O
that	O
a	O
positive	O
current	O
(	O
as	O
created	O
by	O
depolarization	O
of	O
cardiac	O
cells	O
)	O
traveling	O
towards	O
the	O
positive	O
electrode	O
and	O
away	O
from	O
the	O
negative	O
electrode	O
creates	O
a	O
positive	O
deflection	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Likewise	O
,	O
a	O
positive	O
current	O
traveling	O
away	O
from	O
the	O
positive	O
electrode	O
and	O
towards	O
the	O
negative	O
electrode	O
creates	O
a	O
negative	O
deflection	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Then	O
,	O
the	O
direction	O
and	O
magnitude	O
of	O
the	O
blue	O
arrows	O
are	O
what	O
theoretically	O
determine	O
the	O
deflections	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
as	O
a	O
blue	O
arrow	O
on	O
the	O
axis	O
for	O
Lead	O
I	O
moves	O
from	O
the	O
negative	O
electrode	O
,	O
to	O
the	O
right	O
,	O
towards	O
the	O
positive	O
electrode	O
,	O
the	O
ECG	B-Application
line	O
rises	O
,	O
creating	O
an	O
upward	O
wave	O
.	O
</s>
<s>
The	O
greater	O
the	O
magnitude	O
of	O
the	O
blue	O
arrow	O
,	O
the	O
greater	O
the	O
deflection	O
on	O
the	O
ECG	B-Application
for	O
that	O
particular	O
limb	O
lead	O
.	O
</s>
<s>
The	O
SA	O
node	O
is	O
too	O
small	O
for	O
its	O
depolarization	O
to	O
be	O
detected	O
on	O
most	O
ECGs	B-Application
.	O
</s>
<s>
Frames	O
4	O
–	O
10	O
depict	O
the	O
depolarization	O
traveling	O
through	O
the	O
atria	O
,	O
towards	O
the	O
Atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
During	O
frame	O
7	O
,	O
the	O
depolarization	O
is	O
traveling	O
through	O
the	O
largest	O
amount	O
of	O
tissue	O
in	O
the	O
atria	O
,	O
which	O
creates	O
the	O
highest	O
point	O
in	O
the	O
P	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
Like	O
the	O
SA	O
node	O
,	O
the	O
AV	O
node	O
is	O
too	O
small	O
for	O
the	O
depolarization	O
of	O
its	O
tissue	O
to	O
be	O
detected	O
on	O
most	O
ECGs	B-Application
.	O
</s>
<s>
It	O
depicts	O
the	O
depolarization	O
as	O
it	O
starts	O
to	O
travel	O
down	O
the	O
interventricular	O
septum	O
,	O
through	O
the	O
Bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
and	O
Bundle	O
branches	O
.	O
</s>
<s>
After	O
the	O
Bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
the	O
conduction	B-Algorithm
system	I-Algorithm
splits	O
into	O
the	O
left	O
bundle	O
branch	O
and	O
the	O
right	O
bundle	O
branch	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
this	O
gives	O
rise	O
to	O
a	O
negative	O
deflection	O
after	O
the	O
PR	B-Algorithm
interval	I-Algorithm
,	O
creating	O
a	O
Q	O
wave	O
such	O
as	O
the	O
one	O
seen	O
in	O
lead	O
I	O
in	O
the	O
animation	O
to	O
the	O
right	O
.	O
</s>
<s>
This	O
is	O
depicted	O
by	O
frames	O
15	O
–	O
17	O
and	O
results	O
in	O
a	O
positive	O
deflection	O
on	O
all	O
three	O
limb	O
leads	O
,	O
which	O
creates	O
the	O
R	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
Frames	O
18	O
–	O
21	O
then	O
depict	O
the	O
depolarization	O
as	O
it	O
travels	O
throughout	O
both	O
ventricles	O
from	O
the	O
apex	O
of	O
the	O
heart	O
,	O
following	O
the	O
action	O
potential	O
in	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
.	O
</s>
<s>
This	O
phenomenon	O
creates	O
a	O
negative	O
deflection	O
in	O
all	O
three	O
limb	O
leads	O
,	O
forming	O
the	O
S	O
wave	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
Repolarization	O
of	O
the	O
atria	O
occurs	O
at	O
the	O
same	O
time	O
as	O
the	O
generation	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
but	O
it	O
is	O
not	O
detected	O
by	O
the	O
ECG	B-Application
since	O
the	O
tissue	O
mass	O
of	O
the	O
ventricles	O
is	O
so	O
much	O
larger	O
than	O
that	O
of	O
the	O
atria	O
.	O
</s>
<s>
Ventricular	O
contraction	O
occurs	O
between	O
ventricular	B-Application
depolarization	I-Application
and	O
repolarization	O
.	O
</s>
<s>
During	O
this	O
time	O
,	O
there	O
is	O
no	O
movement	O
of	O
charge	O
,	O
so	O
no	O
deflection	O
is	O
created	O
on	O
the	O
ECG	B-Application
.	O
</s>
<s>
This	O
results	O
in	O
the	O
flat	O
ST	B-Algorithm
segment	I-Algorithm
after	O
the	O
S	O
wave	O
.	O
</s>
<s>
This	O
therefore	O
creates	O
a	O
positive	O
deflection	O
in	O
the	O
ECG	B-Application
,	O
and	O
creates	O
the	O
T	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
Ischemia	O
or	O
non-ST	O
elevation	O
myocardial	O
infarctions	O
(	O
non-STEMIs	O
)	O
may	O
manifest	O
as	O
ST	B-Algorithm
depression	I-Algorithm
or	O
inversion	O
of	O
T	B-Algorithm
waves	I-Algorithm
.	O
</s>
<s>
It	O
may	O
also	O
affect	O
the	O
high	O
frequency	O
band	O
of	O
the	O
QRS	B-Algorithm
.	O
</s>
<s>
ST	B-Algorithm
elevation	I-Algorithm
myocardial	O
infarctions	O
(	O
STEMIs	O
)	O
have	O
different	O
characteristic	O
ECG	B-Application
findings	O
based	O
on	O
the	O
amount	O
of	O
time	O
elapsed	O
since	O
the	O
MI	O
first	O
occurred	O
.	O
</s>
<s>
The	O
earliest	O
sign	O
is	O
hyperacute	O
T	B-Algorithm
waves	I-Algorithm
,	O
peaked	O
T	B-Algorithm
waves	I-Algorithm
due	O
to	O
local	O
hyperkalemia	O
in	O
ischemic	O
myocardium	O
.	O
</s>
<s>
This	O
then	O
progresses	O
over	O
a	O
period	O
of	O
minutes	O
to	O
elevations	O
of	O
the	O
ST	B-Algorithm
segment	I-Algorithm
by	O
at	O
least	O
1mm	O
.	O
</s>
<s>
Over	O
a	O
period	O
of	O
hours	O
,	O
a	O
pathologic	O
Q	O
wave	O
may	O
appear	O
and	O
the	O
T	B-Algorithm
wave	I-Algorithm
will	O
invert	O
.	O
</s>
<s>
Over	O
a	O
period	O
of	O
days	O
the	O
ST	B-Algorithm
elevation	I-Algorithm
will	O
resolve	O
.	O
</s>
<s>
The	O
coronary	O
artery	O
that	O
has	O
been	O
occluded	O
can	O
be	O
identified	O
in	O
an	O
STEMI	O
based	O
on	O
the	O
location	O
of	O
ST	B-Algorithm
elevation	I-Algorithm
.	O
</s>
<s>
The	O
left	O
anterior	O
descending	O
(	O
LAD	O
)	O
artery	O
supplies	O
the	O
anterior	O
wall	O
of	O
the	O
heart	O
,	O
and	O
therefore	O
causes	O
ST	B-Algorithm
elevations	I-Algorithm
in	O
anterior	O
leads	O
(	O
V1	O
and	O
V2	O
)	O
.	O
</s>
<s>
The	O
LCx	O
supplies	O
the	O
lateral	O
aspect	O
of	O
the	O
heart	O
and	O
therefore	O
causes	O
ST	B-Algorithm
elevations	I-Algorithm
in	O
lateral	O
leads	O
(	O
I	O
,	O
aVL	O
and	O
V6	O
)	O
.	O
</s>
<s>
The	O
right	O
coronary	O
artery	O
(	O
RCA	O
)	O
usually	O
supplies	O
the	O
inferior	O
aspect	O
of	O
the	O
heart	O
,	O
and	O
therefore	O
causes	O
ST	B-Algorithm
elevations	I-Algorithm
in	O
inferior	O
leads	O
(	O
II	O
,	O
III	O
and	O
aVF	O
)	O
.	O
</s>
<s>
An	O
ECG	B-Application
tracing	O
is	O
affected	O
by	O
patient	O
motion	O
.	O
</s>
<s>
Some	O
rhythmic	O
motions	O
(	O
such	O
as	O
shivering	O
or	O
tremors	B-Application
)	O
can	O
create	O
the	O
illusion	O
of	O
cardiac	B-Application
arrhythmia	I-Application
.	O
</s>
<s>
Accurately	O
separating	O
the	O
ECG	B-Application
artifact	O
from	O
the	O
true	O
ECG	B-Application
signal	O
can	O
have	O
a	O
significant	O
impact	O
on	O
patient	O
outcomes	O
and	O
legal	O
liabilities	O
.	O
</s>
<s>
Improper	O
lead	O
placement	O
(	O
for	O
example	O
,	O
reversing	O
two	O
of	O
the	O
limb	O
leads	O
)	O
has	O
been	O
estimated	O
to	O
occur	O
in	O
0.4	O
%	O
to	O
4%	O
of	O
all	O
ECG	B-Application
recordings	O
,	O
and	O
has	O
resulted	O
in	O
improper	O
diagnosis	O
and	O
treatment	O
including	O
unnecessary	O
use	O
of	O
thrombolytic	O
therapy	O
.	O
</s>
<s>
Whitbread	O
,	O
consultant	O
nurse	O
and	O
paramedic	O
,	O
suggests	O
ten	O
rules	O
of	O
the	O
normal	B-Application
ECG	I-Application
,	O
deviation	O
from	O
which	O
is	O
likely	O
to	O
indicate	O
pathology	O
.	O
</s>
<s>
Rule	O
2	O
:	O
The	O
ST	B-Algorithm
segment	I-Algorithm
(	O
J	O
point	O
)	O
starts	O
on	O
the	O
isoelectric	B-Application
line	I-Application
(	O
except	O
in	O
V1	O
&	O
V2	O
where	O
it	O
may	O
be	O
elevated	O
by	O
not	O
greater	O
than	O
1mm	O
)	O
.	O
</s>
<s>
Rule	O
3	O
:	O
The	O
PR	B-Algorithm
interval	I-Algorithm
should	O
be	O
0.12	O
–	O
0.2	O
seconds	O
long	O
.	O
</s>
<s>
Rule	O
4	O
:	O
The	O
QRS	B-Algorithm
complex	I-Algorithm
should	O
not	O
exceed	O
0.11	O
–	O
0.12	O
seconds	O
.	O
</s>
<s>
Rule	O
5	O
:	O
The	O
QRS	B-Algorithm
and	O
T	B-Algorithm
waves	I-Algorithm
tend	O
to	O
have	O
the	O
same	O
general	O
direction	O
in	O
the	O
limb	O
leads	O
.	O
</s>
<s>
Rule	O
6	O
:	O
The	O
R	B-Algorithm
wave	I-Algorithm
in	O
the	O
precordial	O
(	O
chest	O
)	O
leads	O
grows	O
from	O
V1	O
to	O
at	O
least	O
V4	O
where	O
it	O
may	O
or	O
may	O
not	O
decline	O
again	O
.	O
</s>
<s>
Rule	O
7	O
:	O
The	O
QRS	B-Algorithm
is	O
mainly	O
upright	O
in	O
I	O
and	O
II	O
.	O
</s>
<s>
Rule	O
8	O
:	O
The	O
P	B-Algorithm
wave	I-Algorithm
is	O
upright	O
in	O
I	O
II	O
and	O
V2	O
to	O
V6	O
.	O
</s>
<s>
Rule	O
10	O
:	O
The	O
T	B-Algorithm
wave	I-Algorithm
is	O
upright	O
in	O
I	O
II	O
and	O
V2	O
to	O
V6	O
.	O
</s>
<s>
The	O
end	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
should	O
not	O
drop	O
below	O
the	O
isoelectric	O
baseline	O
.	O
</s>
<s>
Rule	O
11	O
:	O
Does	O
the	O
deepest	O
S	O
wave	O
in	O
V1	O
plus	O
the	O
tallest	O
R	B-Algorithm
wave	I-Algorithm
in	O
V5	O
or	O
V6	O
equal	O
>35mm	O
?	O
</s>
<s>
Rule	O
13	O
:	O
Is	O
there	O
an	O
J	B-Algorithm
wave	I-Algorithm
?	O
</s>
<s>
Numerous	O
diagnoses	O
and	O
findings	O
can	O
be	O
made	O
based	O
upon	O
electrocardiography	B-Application
,	O
and	O
many	O
are	O
discussed	O
above	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
"	O
irregularly	O
irregular	O
"	O
QRS	B-Algorithm
complex	I-Algorithm
without	O
P	B-Algorithm
waves	I-Algorithm
is	O
the	O
hallmark	O
of	O
atrial	B-Application
fibrillation	I-Application
;	O
however	O
,	O
other	O
findings	O
can	O
be	O
present	O
as	O
well	O
,	O
such	O
as	O
a	O
bundle	B-Algorithm
branch	I-Algorithm
block	I-Algorithm
that	O
alters	O
the	O
shape	O
of	O
the	O
QRS	B-Algorithm
complexes	I-Algorithm
.	O
</s>
<s>
ECGs	B-Application
can	O
be	O
interpreted	O
in	O
isolation	O
but	O
should	O
be	O
applied	O
–	O
like	O
all	O
diagnostic	O
tests	O
–	O
in	O
the	O
context	O
of	O
the	O
patient	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
observation	O
of	O
peaked	O
T	B-Algorithm
waves	I-Algorithm
is	O
not	O
sufficient	O
to	O
diagnose	O
hyperkalemia	O
;	O
such	O
a	O
diagnosis	O
should	O
be	O
verified	O
by	O
measuring	O
the	O
blood	O
potassium	O
level	O
.	O
</s>
<s>
Conversely	O
,	O
a	O
discovery	O
of	O
hyperkalemia	O
should	O
be	O
followed	O
by	O
an	O
ECG	B-Application
for	O
manifestations	O
such	O
as	O
peaked	O
T	B-Algorithm
waves	I-Algorithm
,	O
widened	O
QRS	B-Algorithm
complexes	I-Algorithm
,	O
and	O
loss	O
of	O
P	B-Algorithm
waves	I-Algorithm
.	O
</s>
<s>
The	O
following	O
is	O
an	O
organized	O
list	O
of	O
possible	O
ECG-based	O
diagnoses	O
.	O
</s>
<s>
Rhythm	O
disturbances	O
or	O
arrhythmias	B-Application
:	O
</s>
<s>
Heart	B-Algorithm
block	I-Algorithm
and	O
conduction	B-Algorithm
problems	O
:	O
</s>
<s>
In	O
1887	O
,	O
Augustus	O
Waller	O
invented	O
an	O
ECG	B-Application
machine	O
consisting	O
of	O
a	O
Lippmann	O
capillary	O
electrometer	O
fixed	O
to	O
a	O
projector	O
.	O
</s>
<s>
Einthoven	O
also	O
described	O
the	O
electrocardiographic	B-Application
features	O
of	O
a	O
number	O
of	O
cardiovascular	O
disorders	O
.	O
</s>
<s>
In	O
1901	O
,	O
Einthoven	O
,	O
working	O
in	O
Leiden	O
,	O
the	O
Netherlands	O
,	O
used	O
the	O
string	O
galvanometer	O
:	O
the	O
first	O
practical	O
ECG	B-Application
.	O
</s>
<s>
In	O
1924	O
,	O
Einthoven	O
was	O
awarded	O
the	O
Nobel	O
Prize	O
in	O
Medicine	O
for	O
his	O
pioneering	O
work	O
in	O
developing	O
the	O
ECG	B-Application
.	O
</s>
<s>
By	O
1927	O
,	O
General	O
Electric	O
had	O
developed	O
a	O
portable	O
apparatus	O
that	O
could	O
produce	O
electrocardiograms	B-Application
without	O
the	O
use	O
of	O
the	O
string	O
galvanometer	O
.	O
</s>
<s>
In	O
1937	O
,	O
Taro	O
Takemi	O
invented	O
a	O
new	O
portable	O
electrocardiograph	B-Application
machine	O
.	O
</s>
<s>
When	O
added	O
to	O
Einthoven	O
's	O
three	O
limb	O
leads	O
and	O
the	O
six	O
chest	O
leads	O
we	O
arrive	O
at	O
the	O
12-lead	O
electrocardiogram	B-Application
that	O
is	O
used	O
today	O
.	O
</s>
<s>
In	O
the	O
late	O
1940s	O
Rune	O
Elmqvist	O
invented	O
an	O
inkjet	O
printer	O
-	O
thin	O
jets	O
of	O
ink	O
deflected	O
by	O
electrical	O
potentials	O
from	O
the	O
heart	O
,	O
with	O
good	O
frequency	O
response	O
and	O
direct	O
recording	O
of	O
ECG	B-Application
on	O
paper	O
-	O
the	O
device	O
,	O
called	O
the	O
Mingograf	O
,	O
was	O
sold	O
by	O
Siemens	O
Elema	O
until	O
the	O
1990s	O
.	O
</s>
