<s>
The	O
bidomain	B-Algorithm
model	I-Algorithm
is	O
a	O
mathematical	O
model	O
to	O
define	O
the	O
electrical	O
activity	O
of	O
the	O
heart	O
.	O
</s>
<s>
The	O
bidomain	B-Algorithm
model	I-Algorithm
was	O
first	O
proposed	O
by	O
Schmitt	O
in	O
1969	O
before	O
being	O
formulated	O
mathematically	O
in	O
the	O
late	O
1970s	O
.	O
</s>
<s>
Thus	O
,	O
the	O
model	O
results	O
to	O
be	O
a	O
complex	O
one	O
and	O
can	O
be	O
seen	O
as	O
a	O
generalization	O
of	O
the	O
cable	O
theory	O
to	O
higher	O
dimensions	O
and	O
,	O
going	O
to	O
define	O
the	O
so-called	O
bidomain	B-Algorithm
equations	I-Algorithm
.	O
</s>
<s>
Many	O
of	O
the	O
interesting	O
properties	O
of	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
arise	O
from	O
the	O
condition	O
of	O
unequal	O
anisotropy	O
ratios	O
.	O
</s>
<s>
The	O
bidomain	B-Algorithm
domain	O
is	O
principally	O
represented	O
by	O
two	O
main	O
regions	O
:	O
the	O
cardiac	O
cells	O
,	O
called	O
intracellular	O
domain	O
,	O
and	O
the	O
space	O
surrounding	O
them	O
,	O
called	O
extracellular	O
domain	O
.	O
</s>
<s>
The	O
extramyocardial	O
region	O
can	O
be	O
considered	O
as	O
a	O
fluid	O
bath	O
,	O
especially	O
when	O
one	O
wants	O
to	O
simulate	O
experimental	O
conditions	O
,	O
or	O
as	O
a	O
human	B-Algorithm
torso	I-Algorithm
to	O
simulate	O
physiological	O
conditions	O
.	O
</s>
<s>
The	O
boundary	O
of	O
the	O
two	O
principal	O
physical	O
domains	O
defined	O
are	O
important	O
to	O
solve	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
.	O
</s>
<s>
The	O
unknowns	O
in	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
are	O
three	O
,	O
the	O
intracellular	O
potential	O
,	O
the	O
extracellular	O
potential	O
and	O
the	O
transmembrane	O
potential	O
,	O
which	O
is	O
defined	O
as	O
the	O
difference	O
of	O
the	O
potential	O
across	O
the	O
cell	O
membrane	O
.	O
</s>
<s>
Moreover	O
,	O
the	O
membrane	O
capacitance	O
per	O
unit	O
area	O
and	O
the	O
surface	O
to	O
volume	O
ratio	O
of	O
the	O
cell	O
membrane	O
need	O
to	O
be	O
considered	O
to	O
derive	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
formulation	O
,	O
which	O
is	O
done	O
in	O
the	O
following	O
section	O
.	O
</s>
<s>
The	O
bidomain	B-Algorithm
model	I-Algorithm
is	O
defined	O
through	O
two	O
partial	O
differential	O
equations	O
(	O
PDE	O
)	O
the	O
first	O
of	O
which	O
is	O
a	O
reaction	O
diffusion	O
equation	O
in	O
terms	O
of	O
the	O
transmembrane	O
potential	O
,	O
while	O
the	O
second	O
one	O
computes	O
the	O
extracellular	O
potential	O
starting	O
from	O
a	O
given	O
transmembran	O
potential	O
distribution	O
.	O
</s>
<s>
Thus	O
,	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
can	O
be	O
formulated	O
as	O
follows	O
:	O
</s>
<s>
This	O
implies	O
the	O
addition	O
to	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
of	O
an	O
equation	O
describing	O
the	O
potential	O
propagation	O
inside	O
the	O
extramyocardial	O
domain	O
.	O
</s>
<s>
If	O
the	O
extramyocardial	O
region	O
is	O
the	O
human	B-Algorithm
torso	I-Algorithm
,	O
this	O
model	O
gives	O
rise	O
to	O
the	O
forward	B-Algorithm
problem	I-Algorithm
of	I-Algorithm
electrocardiology	I-Algorithm
.	O
</s>
<s>
The	O
bidomain	B-Algorithm
equations	I-Algorithm
are	O
derived	O
from	O
the	O
Maxwell	O
's	O
equations	O
of	O
the	O
electromagnetism	O
,	O
considering	O
some	O
simplifications	O
.	O
</s>
<s>
From	O
here	O
,	O
it	O
is	O
easy	O
to	O
find	O
the	O
second	O
equation	O
of	O
the	O
bidomain	B-Algorithm
model	I-Algorithm
subtracting	O
from	O
both	O
sides	O
.	O
</s>
<s>
There	O
are	O
various	O
possible	O
techniques	O
to	O
solve	O
the	O
bidomain	B-Algorithm
equations	I-Algorithm
.	O
</s>
<s>
Between	O
them	O
,	O
one	O
can	O
find	O
finite	B-Algorithm
difference	I-Algorithm
schemes	I-Algorithm
,	O
finite	B-Application
element	I-Application
schemes	I-Application
and	O
also	O
finite	B-Algorithm
volume	I-Algorithm
schemes	I-Algorithm
.	O
</s>
