Defibrillater

DEFIBRILLATOR

UNIT III

A defibrillator is an electronic device that creates a sustained myocardial depolarization of a patients heart in order to stop ventricular fibrillation or atrial fibrillation

Ventricular fibrillation is a cardiac emergency resulting from asynchronous contraction of heart muscle

It may be due to coronary occlusion, electric shock or abnormalities of body chemistry

This results in fall of CO and leads to death

Ventricular fibrillation can be converted to a more efficient rhythm by applying a high voltage shock to the heart

This sudden voltage then responds to normal physiological pulse and the rhythm is restored

The instrument for administrating the electronic shock is called DEFIBRILLATOR

80 % of patients can be recovered from cardiac arrest using defib with in one min of attack

TYPES

INTERNAL EXTERNAL

INTERNAL

Used when chest is open Large spoon shaped electrodes with

insulated handles are used Magnitude of shock voltage range from

50 V to 1000 V Duration of shock is 2.5 to 5

milliseconds

EXTERNAL DEFIB Used on the chest using paddle shaped

electrodes Bottom of the electrode consists of copper

disc 3-5 cm for kids and 8-10 cm diameter for

adults Insulated handles Voltage range from 1000V to 6000 V Electrode gel is applied Duration 1 to 5 milliseconds

The electrodes are placed in the anterior-anterior position or anterior-posterior position

CLASSIFICATION

Depending on the nature of voltage applied the difibs can be classified in to 6 typesAC DefibrillatorDC DefibrillatorSynchronized DefibrillatorSquare pulse DefibrillatorDouble square pulse DefibrillatorBiphasic DC Defibrillator

The operation of this defibrillator is best explained by beginning with the patient who is wired with four ECG leads placed in the standard position. The EGG waveform information

is processed by the EGG unit to the lower left.

The output waveform is then applied to the QRS detector and the fibrillation detector.

If the QRS is present, a signal will be applied to the upper lead of the upper AND gate. Then if the attendant pushes the defib switch,

placing a signal on the lower lead also, the AND gate will deliver an inhibiting signal to the defibrillator pulse generator. ○ An AND gate generates an output signal only

when stimulus is present on both the upper and the lower input terminals.

If there is no QRS and the fibrillation detector delivers a stimulating pulse to the lower lead of the lower AND gate, then when the attendant activates the defib switch, a stimulus will be put on both terminals of that gate, and its output will trigger the defibrillator. Thus, the defibrillator will deliver a therapeutic current

pulse through the large electrodes on the sternum and apex to the patient’s chest.

Implantable cardioverter-defibrillator An implantable cardioverter-

defibrillator (ICD) is a small battery-powered electrical impulse generator which is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation

The device is programmed to detect cardiac arrhythmia and correct it by delivering a jolt of electricity

The process of implantation of an ICD is similar to implantation of a pacemaker