A defibrillator is a device that delivers an electric shock to the heart to stop ventricular fibrillation or atrial fibrillation, which are abnormal heart rhythms. Ventricular fibrillation occurs when the heart's lower chambers quiver instead of pumping blood, which can be fatal if not treated within minutes by delivering a shock via a defibrillator to reset the heart's rhythm. Defibrillators can be external or internal, and use electric shocks of varying voltages and durations depending on the type and location of use to convert the heart rhythm back to normal.

1. UNIT III

2.  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

5.  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

6.  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

7. TYPES
 INTERNAL
 EXTERNAL

8. 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

10. 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

11.  The electrodes are placed in the
anterior-anterior position or anterior-
posterior position

12. CLASSIFICATION
 Depending on the nature of voltage
applied the difibs can be classified in to
6 types
 AC Defibrillator
 DC Defibrillator
 Synchronized Defibrillator
 Square pulse Defibrillator
 Double square pulse Defibrillator
 Biphasic DC Defibrillator

13.  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.

15.  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.

16.  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.

17. 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