xianfeng song, department of physics, indiana university
DESCRIPTION
Electrical Wave Propagation in a Minimally Realistic Fiber Architecture Model of the Left Ventricle. Xianfeng Song, Department of Physics, Indiana University Sima Setayeshgar, Department of Physics, Indiana University March 17, 2006. This Talk: Outline. Goal Model Construction Results - PowerPoint PPT PresentationTRANSCRIPT
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Electrical Wave Propagation in a Minimally Realistic Fiber Architecture
Model of the Left Ventricle Xianfeng Song, Department of Physics, Indiana University
Sima Setayeshgar, Department of Physics, Indiana University
March 17, 2006
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This Talk: Outline
Goal
Model Construction
Results
Discussion and future plan
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Minimally Realistic Model: Goal
Construct a minimally realistic model of the left ventricle for studying electrical wave propagation in the three dimensional myocardium.
Adequately addresses the role of geometry and fiber architecture on electrical activity in the heart
Simpler and computationally more tractable than fully realistic models
More feasible to incorporate contraction into such a model
Easy to be parallelized and scalable
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Anatomical Heart
A nested layered geometry for the left ventricleA single macroscopic fiber bundle starting at the
basal plane outside the midwall traverses down toward the apex on an outer surface, and at some point before reaching the apex, changes direction, traverses back along an inner surface reinserting at the basal plane inside the midwall.
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Nested Cone Approximation
• A simple nested cone geometry, represents the left
ventricle which does not incorporate the valves.
i=8
e=16
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Fiber construction Construction principles
Peskin Asymptotic Model (Derived by Peskin in 1996) The fiber paths are approximate geodesics on the fiber surfaces.
Requiring the fibers to be circumferential where the double sheets meet at midwall Euler-Lagrange equations (f: fiber trajectory):
Result
'
),,(2
1
f
d
df
dd
dfL
00
z
11
12 sec1
a
Fiber paths on the inner sheet
Fiber paths on the outer sheet
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Governing equations
Governing equation (a conventional parabolic partial differential equation)
Transmembrane current Im was described using a simplified excitable dynamics equations of the FitzHugh-Nagumo type (R. R. Aliev and A. V. Panfilov, 1996)
mm IuDt
uC
)(
1(2
1
aukuvu
v
t
v
uvuaukuIm )1)((
Parameters: a=0.1, 1=0.07,2=0.3,k=8,=0.01, Cm=1
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Diffusion Tensor
2
1
//
00
00
00
p
plocal
D
D
D
D
Local Coordinate Lab Coordinate
Transformation matrix R
RDRD locallab1
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Numerical Implementation
Working in spherical polar coordinates, with the boundaries of the computational domain described by two nested cones, reduces the numerics to computing in a box.
Standard finite differencing is used to treat the spatial derivatives, along with explicit Euler time-stepping
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Parallelize the code
The communication can be minimized when parallelized along the theta direction
Computational results show the model has a very good scalability
CPUsSpeed up
2 1.40
4 3.65
8 7.80
16 15.50
32 29.20
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore
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Finding the filamentFinding all tips
Add current tip into a new filament, marked as the head of this filament
Find the closest unmarked tip
End
Choose an unmarked tip as current tip
Is the distance smaller than a certain
threshold?
Set the closest tip as current tip
Mark the current tip
set reversed=0
Add current tip into current filament
Set the head of current filament as current tip
Is revered=0?
Are there any unmarked tips?
set reversed=1
Definition: Distance between two tips
(1) If two tips are not on a same fiber surface or on adjacent surfaces, the distance is defined to be infinity
(2) Otherwise, the distance is the distance along the fiber surface
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Finding the filament
Finding all tips
Add current tip into a new filament, marked as the head of this filament
Find the closest unmarked tip
End
Choose an unmarked tip as current tip
Is the distance smaller than a certain
threshold?Set the closest tip as current tip
Mark the current tip
set reversed=0Add current tip into
current filament
Set the head of current filament as current tip
Is revered=0?
Are there any unmarked tips?
Set reversed=1
Definition: Distance between two tips
(1) If two tips are not on a same fiber surface or on adjacent surfaces, the distance is defined to be infinity
(2) Otherwise, the distance is the distance along the fiber surface
Yes
No
Yes
Yes
No
No
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Result - Simulation
FHN Model:
Color denotes the u variable in FHN model. The movie shows the spread of excitation in the cone shaped model.
Filament initially
The filament after break up
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Result - Convergence
Filament number and Filament length vs Heart size
As the mesh size decreases, the quantitive behavior convergent to a certain value
The result for dr=0.7 agree with the result for dr=0.5 within the error
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Result - Filaments
Both filament length
Scaling of ventricular turbulence. The log of the total length and the log of the number of filaments both have linear relationship with log of heart size, but with different scale factor.
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Discussion and Conclusion
We constructed a minimally realistic model of the left ventricle for studying electrical wave propagation in the three dimensional myocardium and developed a stable filament finding algorithm based on this model
The model can adequately address the role of geometry and fiber architecture on electrical activity in the heart, which qualitatively agree with fully realistic model
The model is more computational tractable and easily to show the convergence
The model adopts simple difference scheme, which makes it more feasible to incorporate contraction into such a model
The model can be easily parallelized, and has a very good scalability
Xianfeng Song, Indiana University, Bloomington, March APS Meeting 2006, Baltimore