70752570 arrythmia simulator

7/29/2019 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

70752570 arrythmia simulator

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