Engr. Hinesh Kumar

Fibrillation and Defibrillator

Defibrillation was invented in 1899 by Prevost and Batelli, two Italian physiologists.

They discovered that electric shocks could convert ventricular fibrillation to sinus rhythm in dogs.

The first case of a human life saved by defibrillation was reported by Beck in 1947 .

History

Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibers.

There are two major classes of cardiac fibrillation: Atrial Fibrillation and Ventricular Fibrillation.

Atrial fibrillation is an irregular and uncoordinated contraction of the cardiac muscle of atria.

Ventricular Fibrillation is an irregular and uncoordinated contraction of the cardiac muscle of ventricles.

Fibrillation

Fibrillation

Figure: (a)Normal waveform. (b)Ventricular fibrillation. (c)Ventricular tachycardia.

Defibrillation is a process in which an electronic device sends an electric shock to the heart to stop an extremely rapid, irregular heartbeat, and restore the normal heart rhythm.

Defibrillation should be performed with in the first 8 minutes after cardiac arrest. Ideally, the sooner, the better.

Defibrillation

Defibrillator is the device used to deliver the electrical shock and it can be manual or automatic.

Defibrillator

Internal DefibrillatorElectrodes directly placed to the hearte.g., ICD (Internal Cardioversion Defibrillator)

External DefibrillatorElectrodes placed directly on the chest.e.g., AED (Automatic External Defibrillator)

Types of Defibrillator

Internal External

An implantable cardioverter-defibrillator (often called an ICD) is a device that briefly passes an electric current through the heart.

It is "implanted," or put in your body surgically.

It includes a pulse generator and one or more leads.

The pulse generator constantly watches your heartbeat.

Internal Defibrillator

AED is a portable electronic device that automatically diagnoses the ventricular fibrillation in a patient.

Automatic refers to the ability to autonomously analyse the patient's condition.

AEDs require self-adhesive electrodes instead of hand held paddles.

Automated External Defibrillator

Circiut Diagram

Cardoiversion after defibrillation

There are two general classes of waveforms:

a) Monophasic waveform • Energy delivered in one direction through

the patient’s heart

b) Biphasic waveform• Energy delivered in both direction through

the patient’s heart

Classification of Waveform

A monophasic type, give a high-energy shock, up to 10 to 360 joules due to which increased cardiac injury and in burns the chest around the shock pad sites.

Monophasic Waveform

A biphasic type, give two sequential lower-energy shocks of 5 - 200 joules, with each shock moving in an opposite polarity between the pads.Low energy biphasic shocks may be as effective as

high energy monophasic shocks.Biphasic waveform defibrillation used in implantable

cardioverter defibrillator (ICD) and automatic external defibrillators.

Biphasic Waveform

1. Lown Waveform2. Monopulse Waveform3. Tapered DC Delay4. Trapezoidal

Defibrillator Waveform

In 1962, Dr Bernard Lown of Harward University introduced the waveform that bears his name.

The voltage and current applied to the patient's chest plotted against time.

The current will rise very rapidly to about 20 A under the influence of slightly less than 3 KV.

The waveform then decays back to zero within 5 ms, and then produces a smaller negative pulse also of about 5 msec.

The charge delivered to the patient is stored in a capacitor and is produced by a high-voltage dc power supply.

Lown Waveform

Figure…

Lown Defibrillator Waveform

The operator can set the charge level using the set energy knob on the front panel.

The knob controls the dc voltage produced by the high-voltage power supply and so can set the maximum charge on the capacitor

The energy stored in the capacitor is given by:

where,U is the energy in joules (J) C is the capacitance of C1, in farads (F) V is the voltage across C1, (V)

Cont…

Calculate the energy stored in a 16-µF capacitor that is charged to a potential of 5000 V dc.

Solution

Exercise

The monopulse waveform shown in figure is a modified Lown waveform and is commonly found in certain portable defibrillator.

Monopulse Waveform

This waveform differs from the others in that it uses a lower amplitude and longer duration to achieve the energy level.

The energy transferred is proportional to the area under the square of the curve, so we may attain the same energy as in other waveforms.

Tapered DC Delay

The trapezoidal waveform shown in figure is another low-voltage, long duration shape.

The initial output potential is about 800 V, which drops continuously for about 20 ms until it reaches 500 V, where it is terminated .

Trapezoidal

Types of defibrillator electrodes:-

a) Spoon Shaped Electrode Applied directly to the heart.

b) Paddle type electrode Applied against the chest wall

c) Pad Type Electrode Applied directly on chest wall

Defibrillator Electrodes

fig: Electrodes used in defibrillator (a) a spoon shaped internal electrode that is applied directly to the heart. (b) a paddle type

electrode applied against the anterior chest wall.

Fig.- Pad electrode

White is negative, anterior chest wall.Red is Positive , left anterior axillary line.

“Red on Ribs! White on right!”

Placement

• The paddles used in the procedure should not be placed:-• on a woman's breasts • over an internal pacemaker patients.

• Before the paddle is used, a electrochemical gel must be applied to the patient's skin to avoid the skin burns.

Precautions

• Skin burns from the defibrillator paddles are the most common complication of defibrillation.

• Other risks include injury to the heart muscle, abnormal heart rhythms, and blood clots.

RISKS

Attach the external and internal paddles if the monitor reads, "No paddles”.

Check to ensure that the leads are securely attached if the monitor reads, "No leads.“

Connect the unit to AC power if the message reads, "Low battery.“

Verify that the Energy Select control settings are correct if the defibrillator does not charge.

Troubleshooting

Change the electrodes and make sure that the electrodes adapter cable is properly connected.

Close the recorder door and the paper roll if the monitor message reads, "Check recorder”.

Cont…

Thankyou