<s>
In	O
electrocardiography	B-Application
,	O
the	O
T	B-Algorithm
wave	I-Algorithm
represents	O
the	O
repolarization	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
The	O
interval	O
from	O
the	O
beginning	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
to	O
the	O
apex	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
is	O
referred	O
to	O
as	O
the	O
absolute	O
refractory	O
period	O
.	O
</s>
<s>
The	O
last	O
half	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
is	O
referred	O
to	O
as	O
the	O
relative	O
refractory	O
period	O
or	O
vulnerable	O
period	O
.	O
</s>
<s>
The	O
T	B-Algorithm
wave	I-Algorithm
contains	O
more	O
information	O
than	O
the	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
The	O
T	B-Algorithm
wave	I-Algorithm
can	O
be	O
described	O
by	O
its	O
symmetry	O
,	O
skewness	O
,	O
slope	O
of	O
ascending	O
and	O
descending	O
limbs	O
,	O
amplitude	O
and	O
subintervals	O
like	O
the	O
Tpeak	O
–	O
Tend	O
interval	O
.	O
</s>
<s>
In	O
most	O
leads	O
,	O
the	O
T	B-Algorithm
wave	I-Algorithm
is	O
positive	O
.	O
</s>
<s>
During	O
ventricle	O
contraction	O
(	O
QRS	B-Algorithm
complex	I-Algorithm
)	O
,	O
the	O
heart	O
depolarizes	O
.	O
</s>
<s>
But	O
this	O
negative	O
flow	O
causes	O
a	O
positive	O
T	B-Algorithm
wave	I-Algorithm
;	O
although	O
the	O
cell	O
becomes	O
more	O
negatively	O
charged	O
,	O
the	O
net	O
effect	O
is	O
in	O
the	O
positive	O
direction	O
,	O
and	O
the	O
ECG	B-Application
reports	O
this	O
as	O
a	O
positive	O
spike	B-Algorithm
.	O
</s>
<s>
However	O
,	O
a	O
negative	O
T	B-Algorithm
wave	I-Algorithm
is	O
normal	O
in	O
lead	O
aVR	O
.	O
</s>
<s>
Lead	O
V1	O
generally	O
have	O
a	O
negative	O
T	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
In	O
addition	O
,	O
it	O
is	O
not	O
uncommon	O
to	O
have	O
a	O
negative	O
T	B-Algorithm
wave	I-Algorithm
in	O
lead	O
III	O
,	O
aVL	O
,	O
or	O
aVF	O
.	O
</s>
<s>
A	O
periodic	O
beat-to-beat	O
variation	O
in	O
the	O
amplitude	O
or	O
shape	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
may	O
be	O
termed	O
T	B-Algorithm
wave	I-Algorithm
alternans	I-Algorithm
.	O
</s>
<s>
Nerves	O
that	O
innervate	O
skeletal	O
muscle	O
have	O
an	O
extremely	O
short	O
refractory	O
period	O
after	O
being	O
subjected	O
to	O
an	O
action	B-Algorithm
potential	I-Algorithm
(	O
of	O
the	O
order	O
of	O
1	O
ms	O
)	O
.	O
</s>
<s>
This	O
prevents	O
the	O
heart	O
from	O
undergoing	O
sustained	O
contractions	O
because	O
it	O
forces	O
the	O
refractory	O
period	O
and	O
cardiac	B-Algorithm
action	I-Algorithm
potential	I-Algorithm
firing	O
to	O
be	O
of	O
the	O
same	O
length	O
of	O
time	O
.	O
</s>
<s>
Once	O
the	O
action	B-Algorithm
potential	I-Algorithm
is	O
over	O
,	O
potassium	O
ions	O
flow	O
out	O
of	O
the	O
cell	O
due	O
to	O
increased	O
cell	O
membrane	O
permeability	O
to	O
those	O
ions	O
.	O
</s>
<s>
This	O
repolarization	O
occurs	O
quickly	O
enough	O
that	O
another	O
action	B-Algorithm
potential	I-Algorithm
can	O
cause	O
depolarization	O
before	O
the	O
last	O
action	B-Algorithm
potential	I-Algorithm
has	O
dissipated	O
.	O
</s>
<s>
This	O
causes	O
the	O
repolarization	O
to	O
occur	O
more	O
slowly	O
,	O
making	O
the	O
refractory	O
period	O
as	O
long	O
as	O
the	O
action	B-Algorithm
potential	I-Algorithm
,	O
preventing	O
sustained	O
contractions	O
.	O
</s>
<s>
The	O
T	B-Algorithm
wave	I-Algorithm
is	O
representative	O
of	O
the	O
repolarization	O
of	O
the	O
membrane	O
.	O
</s>
<s>
In	O
an	O
EKG	B-Application
reading	O
,	O
the	O
T	B-Algorithm
wave	I-Algorithm
is	O
notable	O
because	O
it	O
must	O
be	O
present	O
before	O
the	O
next	O
depolarization	O
.	O
</s>
<s>
An	O
absent	O
or	O
strangely	O
shaped	O
T	B-Algorithm
wave	I-Algorithm
may	O
signify	O
disruption	O
in	O
repolarization	O
or	O
another	O
segment	O
of	O
the	O
heartbeat	O
.	O
</s>
<s>
Normally	O
,	O
T	B-Algorithm
waves	I-Algorithm
are	O
upright	O
in	O
all	O
leads	O
,	O
except	O
aVR	O
,	O
aVL	O
,	O
III	O
and	O
V1	O
leads	O
.	O
</s>
<s>
Highest	O
amplitude	O
of	O
T	B-Algorithm
wave	I-Algorithm
is	O
found	O
at	O
V2	O
and	O
V3	O
leads	O
.	O
</s>
<s>
The	O
shape	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
is	O
usually	O
asymmetrical	O
with	O
a	O
rounded	O
peak	O
.	O
</s>
<s>
T	B-Algorithm
wave	I-Algorithm
inversions	O
from	O
V2	O
to	O
V4	O
leads	O
are	O
frequently	O
found	O
and	O
normal	O
in	O
children	O
.	O
</s>
<s>
In	O
normal	O
adults	O
,	O
T	B-Algorithm
wave	I-Algorithm
inversions	O
from	O
V2	O
to	O
V3	O
are	O
less	O
commonly	O
found	O
but	O
can	O
be	O
normal	O
.	O
</s>
<s>
The	O
depth	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
also	O
becomes	O
progressively	O
shallow	O
from	O
one	O
to	O
the	O
next	O
lead	O
.	O
</s>
<s>
The	O
height	O
of	O
the	O
T	B-Algorithm
wave	I-Algorithm
should	O
not	O
exceed	O
5mm	O
in	O
limb	O
leads	O
and	O
more	O
than	O
10mm	O
in	O
precordial	O
leads	O
.	O
</s>
<s>
Both	O
the	O
abnormalities	O
of	O
the	O
ST	B-Algorithm
segment	I-Algorithm
and	O
T	B-Algorithm
wave	I-Algorithm
represents	O
the	O
abnormalities	O
of	O
the	O
ventricular	B-Application
repolarization	I-Application
or	O
secondary	O
to	O
abnormalities	O
in	O
ventricular	O
depolarisation	O
.	O
</s>
<s>
Inverted	O
T	B-Algorithm
wave	I-Algorithm
is	O
considered	O
abnormal	O
if	O
inversion	O
is	O
deeper	O
than	O
1.0mm	O
.	O
</s>
<s>
Inverted	O
T	B-Algorithm
waves	I-Algorithm
found	O
in	O
leads	O
other	O
than	O
the	O
V1	O
to	O
V4	O
leads	O
is	O
associated	O
with	O
increased	O
cardiac	O
deaths	O
.	O
</s>
<s>
Inverted	O
T	B-Algorithm
waves	I-Algorithm
associated	O
with	O
cardiac	O
signs	O
and	O
symptoms	O
(	O
chest	O
pain	O
and	O
cardiac	O
murmur	O
)	O
are	O
highly	O
suggestive	O
of	O
myocardial	O
ischaemia	O
.	O
</s>
<s>
Other	O
ECG	B-Application
changes	O
associate	O
with	O
myocardial	O
ischaemia	O
are	O
:	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
with	O
an	O
upright	O
T	B-Algorithm
wave	I-Algorithm
;	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
with	O
biphasic	O
T	B-Algorithm
wave	I-Algorithm
or	O
inverted	O
T	B-Algorithm
wave	I-Algorithm
with	O
negative	O
QRS	B-Algorithm
complex	I-Algorithm
;	O
T	B-Algorithm
wave	I-Algorithm
symmetrically	O
inverted	O
with	O
a	O
pointed	O
apex	O
,	O
while	O
the	O
ST	B-Algorithm
segment	I-Algorithm
is	O
either	O
bowed	O
upwards	O
or	O
horizontally	O
depressed	O
,	O
or	O
not	O
deviated	O
;	O
and	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
progressing	O
to	O
abnormal	O
T	B-Algorithm
wave	I-Algorithm
during	O
ischaemia	O
free	O
intervals	O
.	O
</s>
<s>
However	O
,	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
is	O
not	O
suggestive	O
of	O
ischaemic	O
location	O
of	O
the	O
heart	O
.	O
</s>
<s>
ST	B-Algorithm
segment	I-Algorithm
depression	O
in	O
eight	O
or	O
more	O
leads	O
,	O
associated	O
with	O
ST	B-Algorithm
segment	I-Algorithm
elevation	O
in	O
aVR	O
and	O
V1	O
are	O
associated	O
with	O
left	O
main	O
coronary	O
artery	O
disease	O
or	O
three-vessel	O
disease	O
(	O
blockage	O
of	O
all	O
three	O
major	O
branches	O
of	O
coronary	O
arteries	O
)	O
.	O
</s>
<s>
ST	B-Algorithm
segment	I-Algorithm
depression	O
most	O
prominent	O
from	O
V1	O
to	O
V3	O
is	O
suggestive	O
of	O
posterior	O
infarction	O
.	O
</s>
<s>
Furthermore	O
,	O
tall	O
or	O
wide	O
QRS	B-Algorithm
complex	I-Algorithm
with	O
an	O
upright	O
T	B-Algorithm
wave	I-Algorithm
is	O
further	O
suggestive	O
of	O
the	O
posterior	O
infarction	O
.	O
</s>
<s>
Wellens	O
 '	O
syndrome	O
is	O
caused	O
by	O
the	O
injury	O
or	O
blockage	O
of	O
the	O
left	O
anterior	O
descending	O
artery	O
,	O
therefore	O
resulting	O
in	O
symmetrical	O
T	B-Algorithm
wave	I-Algorithm
inversions	O
from	O
V2	O
to	O
V4	O
with	O
depth	O
more	O
than	O
5mm	O
in	O
75%	O
of	O
the	O
cases	O
.	O
</s>
<s>
Meanwhile	O
,	O
the	O
remaining	O
25%	O
of	O
the	O
cases	O
shows	O
biphasic	O
T	B-Algorithm
wave	I-Algorithm
morphology	O
.	O
</s>
<s>
ST	B-Algorithm
segments	I-Algorithm
remains	O
neutral	O
in	O
this	O
syndrome	O
.	O
</s>
<s>
An	O
episode	O
of	O
chest	O
pain	O
in	O
Wellens	O
 '	O
syndrome	O
is	O
associated	O
with	O
ST	O
elevation	O
or	O
depression	O
and	O
later	O
progressed	O
to	O
T	B-Algorithm
wave	I-Algorithm
abnormality	O
after	O
chest	O
pain	O
subsided	O
.	O
</s>
<s>
T	B-Algorithm
wave	I-Algorithm
inversion	O
less	O
than	O
5mm	O
may	O
still	O
represents	O
myocardial	O
ischaemia	O
,	O
but	O
is	O
less	O
severe	O
than	O
Wellens	O
 '	O
syndrome	O
.	O
</s>
<s>
ECG	B-Application
would	O
be	O
abnormal	O
in	O
75	O
to	O
95%	O
of	O
the	O
patients	O
.	O
</s>
<s>
Characteristic	O
ECG	B-Application
changes	O
would	O
be	O
large	O
QRS	B-Algorithm
complex	I-Algorithm
associated	O
with	O
giant	O
T	B-Algorithm
wave	I-Algorithm
inversion	O
in	O
lateral	O
leads	O
I	O
,	O
aVL	O
,	O
V5	O
,	O
and	O
V6	O
,	O
together	O
with	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
in	O
left	O
ventricular	O
thickening	O
.	O
</s>
<s>
For	O
right	O
ventricular	O
thickening	O
,	O
T	B-Algorithm
waves	I-Algorithm
are	O
inverted	O
from	O
V2	O
to	O
V3	O
leads	O
.	O
</s>
<s>
ST	O
and	O
T	B-Algorithm
waves	I-Algorithm
changes	O
may	O
not	O
be	O
apparent	O
in	O
hypertrophic	O
cardiomyopathy	O
,	O
but	O
if	O
there	O
is	O
presence	O
of	O
ST	O
and	O
T	B-Algorithm
waves	I-Algorithm
changes	O
indicates	O
severe	O
hypertrophy	O
or	O
ventricular	O
systolic	O
dysfunction	O
.	O
</s>
<s>
According	O
to	O
Sokolow-Lyon	O
criterion	O
,	O
the	O
height	O
of	O
R	B-Algorithm
wave	I-Algorithm
in	O
V5	O
or	O
V6	O
+	O
the	O
height	O
of	O
S	O
wave	O
in	O
V1	O
more	O
than	O
35mm	O
would	O
be	O
suggestive	O
of	O
left	O
ventricular	O
hypertrophy	O
.	O
</s>
<s>
Both	O
right	O
and	O
left	O
bundle	B-Algorithm
branch	I-Algorithm
blocks	I-Algorithm
are	O
associated	O
with	O
similar	O
ST	O
and	O
T	B-Algorithm
wave	I-Algorithm
changes	O
as	O
in	O
hypertrophic	O
cardiomyopathy	O
,	O
but	O
are	O
opposite	O
to	O
the	O
direction	O
of	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
In	O
pulmonary	O
embolism	O
,	O
T	B-Algorithm
wave	I-Algorithm
can	O
be	O
symmetrically	O
inverted	O
at	O
V2	O
to	O
V4	O
leads	O
but	O
sinus	B-Algorithm
tachycardia	I-Algorithm
is	O
usually	O
the	O
more	O
common	O
finding	O
.	O
</s>
<s>
T	B-Algorithm
wave	I-Algorithm
inversion	O
is	O
only	O
present	O
in	O
19%	O
of	O
mild	O
pulmonary	O
embolism	O
,	O
but	O
the	O
T	O
inversion	O
can	O
be	O
present	O
in	O
85%	O
of	O
the	O
cases	O
in	O
severe	O
pulmonary	O
embolism	O
.	O
</s>
<s>
Inversion	O
of	O
T	B-Algorithm
waves	I-Algorithm
in	O
most	O
of	O
the	O
ECG	B-Application
leads	O
except	O
aVR	O
indicates	O
many	O
causes	O
most	O
commonly	O
myocardial	O
ischaemia	O
and	O
intracranial	O
haemorrhage	O
.	O
</s>
<s>
Others	O
include	O
:	O
hypertrophic	O
cardiomyopathy	O
,	O
Takotsubo	O
cardiomyopathy	O
(	O
stress-induced	O
cardiomyopathy	O
)	O
,	O
cocaine	B-Application
abuse	O
,	O
pericarditis	O
,	O
pulmonary	O
embolism	O
,	O
and	O
advanced	O
or	O
complete	O
atrioventricular	O
block	O
.	O
</s>
<s>
As	O
the	O
name	O
suggests	O
,	O
Biphasic	O
T	B-Algorithm
waves	I-Algorithm
move	O
in	O
opposite	O
directions	O
.	O
</s>
<s>
Wellens	O
 '	O
Syndrome	O
is	O
a	O
pattern	O
of	O
biphasic	O
T	B-Algorithm
waves	I-Algorithm
in	O
V2	O
–	O
3	O
.	O
</s>
<s>
T	B-Algorithm
wave	I-Algorithm
is	O
considered	O
flat	O
when	O
the	O
wave	O
varies	O
from	O
-1.0mm	O
to	O
+	O
1.0mm	O
in	O
height	O
.	O
</s>
<s>
Hypokalemia	O
or	O
digitalis	O
therapy	O
can	O
cause	O
flattened	O
T	B-Algorithm
wave	I-Algorithm
with	O
a	O
prominent	O
U	B-Algorithm
wave	I-Algorithm
.	O
</s>
<s>
As	O
hypokalemia	O
progressively	O
worsens	O
,	O
T	B-Algorithm
wave	I-Algorithm
becomes	O
more	O
flatten	O
while	O
U	B-Algorithm
wave	I-Algorithm
becomes	O
more	O
prominent	O
,	O
with	O
progressively	O
deeper	O
ST	B-Algorithm
segment	I-Algorithm
depression	O
.	O
</s>
<s>
For	O
digitalis	O
toxicity	O
,	O
there	O
will	O
be	O
sagging	O
QT	B-Algorithm
interval	I-Algorithm
,	O
flattened	O
T	B-Algorithm
wave	I-Algorithm
,	O
and	O
prominent	O
U	B-Algorithm
wave	I-Algorithm
with	O
a	O
shortened	O
QT	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
These	O
T	B-Algorithm
waves	I-Algorithm
may	O
be	O
seen	O
in	O
patients	O
displaying	O
Prinzmetal	O
angina	O
.	O
</s>
<s>
The	O
name	O
of	O
these	O
T	B-Algorithm
waves	I-Algorithm
suggests	O
the	O
shape	O
it	O
exhibits	O
(	O
double	O
peaks	O
)	O
.	O
</s>
<s>
Since	O
these	O
T	B-Algorithm
wave	I-Algorithm
abnormalities	O
may	O
arise	O
from	O
different	O
events	O
,	O
i.e.	O
</s>
