70752570 arrythmia simulator
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ARRHYTHMIA
SIMULATOR
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Introduction
Two mechanisms that produce arrhythmias are automaticityand conductivity.
These physiological properties of cardiac cells are represented by
a phase response curve and an excitability recovery curve,respectively.
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Defibrillator
Electrophysiological stimulationSinus
Atrium
AV node
Ventricle
Atrial ectopic focus
Ventricular ectopic focus
User commandantegrade conduction
retrograde conductionextra stimuli
Figure 1. Cardiac model using six types of
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Description of the system
The simulation system consisted of the cardiac module
The cardiac module was composed of six types of autorhythmic
cardiac cells (Fig. 1).
The cardiac cells run independently at every timer event from
the cardiac module.The antegrade and retrograde conduction between these cells
were controlled by the user's operation on the check boxes in the
window.
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Model of cardiac cells
Electrophysiological properties of the cardiac autorhythmic
cells are characterized by the automaticity and conductivity. Theautorhythmic cells can periodically generate spontaneous
electrical impulses.
The oscillatory systems have a phase dependent property; theresponse of the cell to the external stimuli varies depending on
the phase at which the stimuli were applied.
The conductivity is represented by an excitability recoverycurve (ERC). The ERC of the AV-node, AV-nodal conduction
curve, defines the conduction delay and a timing to stimulate the
ventricle in this system
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ac
b
w
Figure 2. Electrophysiological properties of the
cardiac cell. PRC(left) and ERC(right).
Xmin
Ymin
Y0
T0
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PRC
The PRC that specified the cell activity was defined by four
parameters, slopes of three line (a,c,b), and intersection on the
time axis (w) by the line c.
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ERC
The ERC was approximated by the decaying exponential
functionconduction time = (Y0-Ymin)*Exp(-(x-Xmin)/T0) +Ymin,where x is the extrastimulus coupling interval (H1A2), Xmin
corresponds to the effective refractory period, Y0 is a maximum
connection delay at Xmin, Ymin means an intrinsic conductiontime, and T0 means a time constant of the curve. For simplicity,
these parameters are not dependent on the autorhythmic rate.
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Figure 3. Sample window: normal state
of the heart.
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Figure 3 shows the control panel and the ECG panel of
the cardiac module. Each electrical activity of the cells is drawnat the predefined position on a ladder diagram. The predicted
conduction is drawn with a blue line at the activation of the cell.
The slanted yellow lines show the spread of activation
transmitted actually. The ECG waveforms are drawn in real timeas the integrated activity of all cells.
In addition, the dynamic state of contraction and relaxation of
the atrium and the ventricle are presented graphically.
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Figure 4. Wenckebach sequence
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Figure 4 shows a Wenckebach sequence with 5:4 ratios
produced by the special condition of the ERC of the AV-node at a
sinus rate of 70/min. User could modify the parameters of PRC
and ERC in the dialog box.Figure 5 shows a simulation of cardiac rhythm disturbances
induced by the conduction between the atrium and the ectopic
focus.
Figure 6 shows the ECG sequence of the ventricular flutter,
fibrillation, and the defibrillation procedure achieved by the user
operation. It shows a pause period caused by the defibrillationthat resumed all the activity of the heart.
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Figure 5. Reentry in the atrium
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Figure 6. Defibrillation
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