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