Defibrillator.pptx. Jei3j

UNIT OUTCOME 3
• Need of defibrillator
• DC Defibrillator
• AED (advisory external defibrillator )
• Implantable Defibrillator
• Defibrillator electrodes

Need of defibrillator
Life-threatening cardiac arrhythmias specifically ventricular fibrillation (V-Fib) and
non-perfusing ventricular tachycardia (V-Tach).
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or
dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too
slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is
called tachycardia, and a resting heart rate that is too slow – below 60 beats per
minute – is called bradycardia.
Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the
ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular
fibrillation results in cardiac arrest with loss of consciousness and no pulse. This is
followed by sudden cardiac death in the absence of treatment. Ventricular fibrillation
is initially found in about 10% of people with cardiac arrest.
Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower
chambers of the heart.Although a few seconds of VT may not result in permanent
problems, longer periods are dangerous; and multiple episodes over a short period of
time are referred to as an electrical storm. lightheadedness, palpitations, or chest pain.
Ventricular tachycardia may result in ventricular fibrillation (VF) and turn into
cardiac arrest. It is found initially in about 7% of people in cardiac arrest.

NEED OF DEFIBRILLATOR
Ventricular fibrillation is serious cardiac emergency resulting from
asynchronous contraction of heart muscle. This uncoordinated movement
of ventricle walls of the heart may result from electric shock or from
abnormalities of body chemistry.
Main problem of fibrillation is continuously stimulation of adjacent cells of
heart muscle fibers. So there is no synchronized succession of events that
follow heart action.
This Fibrillation leads to loss of cardiac output and irreversible brain damage
or death if not reversed within 5 minutes of onset
Ventricular fibrillation can be converted into more efficient rhythm by applying
a high energy shock to the heart. This sudden surge across the heart
cause all muscle fibers to contract simultaneously ,possibly the fibers
then respond to normal physiological intrinsic pulse.

What is Cardioversion
Defibrillator is a device that deliver a
therapeutic dose of electrical energy (electric
shock) to the affected heart (fibrillated heart
or other shockable rhythm) to force the heart
to produce normal cardiac rhythm.
It is any process that aims to convert an
arrhythmia back to sinus rhythm by
therapeutic dose of electrical energy
Unlike defibrillation, which is used in cardiac
arrest patients, synchronized cardioversion is
performed on patients that still have a pulse
What is defibrillator

DEFIBRILLATION VS. CARDIO
VERSION

DC
DEFIBRILLATOR
Variable Auto transformer T1:
 Forms primary of high voltage of transformer T2.
 T1 variable autotransformer is usually designed with a significant number of
primary windings to produce a secondary voltage for T2 which can be
adjusted from a few volts
 Auto transformers ensure a consistent linear regulation of AC voltage to
provide high output and negligible waveform distortion.
Step-up transformer T2:
 It forms secondary of variable auto transformer T2.
 A transformer transfers power from the primary coil to the secondary coil.
 Since the power must stay the same, if the voltage increases, the current
must decrease. (P=VI)
Diode Rectifier:
The output voltage of the transformer is rectified and is connected
to
vacuum type high voltage change-over switch.
It converts an alternating current into a direct one by allowing a current to
flow through it in one direction only.

DC
DEFIBRILLATOR
Switch:
 It is a vacuum type high voltage change over switch.
 Its one end is connected to Diode rectifier at 1 and another to one end of an oil-filled
16 micro-farad capacitor.
 In position A the capacitor charges to a voltage set by the positioning of the auto
transformer.
 When the high voltage switch changes over the position 2, the capacitor is discharged
across the heart through the electrodes.
Capacitor:
 Oil filled 16 micro farad capacitor is used.
 During transthoracic defibrillation an energy storage capacitor is charged at relatively
slow rate in order of seconds by means of step-up transformer and then delivered
rapid rate in order of milliseconds to the chest of the patient.
Inductor:
 The rapid discharge rate impairs(weaken/damage) the contractibility of ventricles.
To overcome it, a current limiting inductor is inserted in series with the patient circuit.
The inductor slows down the discharge from the capacitor by the induced counter
voltage.
 This gives the output pulse a physiologically favorable shape.

Block Diagram of DC defibrillator
POWER
SUPPLY
CHARGING
CIRCUIT
ENERGY
STORAGE
WAVEFORM
SHAPING
CHARGE
CONTROL
DISCHARGE
CONTROL
AC
POWER
SOURCE
USER INPUT
TO PATIENT
PADDLE

Energy: E=1/2 CV2
C= 16 microfarad
E= 400 Ws
V= 7000V with load resistance 50-200 ohms
For internal defibrillation E= 100Ws with load
resistance 25-50 ohms
Most of the defibrillator will deliver between
60% and 80% of their stored energy to a 50
ohms load.

• The shape of the waveform
that appears across electrodes
will depend
on the value of capacitor and
the
inductor used in the circuit (100mH).
• The discharge resistance which patient
represents for the defibrillating pulse
may be regarded as purely 50 to 100
ohms with electrode size 80cm2.
• The most common waveform utilized
in the RLC circuit employs an under
damped response with damping factor
less than unity.
• This particular waveform is called as
Lown waveform.
• This waveform is more or less of an
oscillatory character, with both
positive and negative portions.
LOWN
WAVEFORM

MONOPHASIC VS BIPHASIC DEFIBRILLATION
Terms
Monophasic Defibrillators Biphasic Defibrillators
Definition
The type waveform formed
during this process where the
shock gets delivered to the
heart with the help of just one
vector and hence gets the
name.
The type waveform formed
during this process where the
shock gets delivered to the
heart with the aid of two
vectors and hence gets the
name.
Usage
Different life-threatening cardiac
dysrhythmias and ventricular
fibrillation.
Various life-threatening
cardiac dysrhythmias and
ventricular fibrillation.
Devices Implantable Defibrillators
detects the irregular heart
rate.
External Defibrillators moves
the high-level values without
any problems
Nature Most common used process.
Most common available
process.
Energy On a monophasic defibrillator, this is
On a biphasic defibrillator, this
is usually between 120 joules

IMPLANTABLE
DEFIBRILLATOR
• The use of automatic implantable defibrillator (AID) is recommended for
patients who are at high risk for ventricular fibrillation.
• It used integrated circuits to reduce the device size.
• It has enhancing functionality of the device.
• It has ability to store recording of the patient’s heart
signals and collects extensive therapy history and
diagnostic data files.
• This device is hermetically(airtight) sealed, biocompatible,
and able to survive a temperature range of -30 degree Celsius
to 60 degree Celsius.
• This device allows the physician to non-invasively program it.
• It has sophisticated algorithms for rhythm classification and
storage of patient’s heart signal.

IMPLANTABLE
DEFIBRILLATOR
• An implantable defibrillator is continuously monitors a patient’s heart rhythm.
• If the device detects fibrillation, the capacitor within the device are charged up to 750
V.
• The capacitor then discharged into the heart which mostly represents a resistive load of
50 ohm and to bring the heart into normal rhythm.
• The shock duration is approximately 4-8 ms which results in the delivery of
approximately 30-35 J at 750 volts.
Implantable defibrillator system have main system component:
1. AID
2. The Lead system
3. The programmer recorder/monitor (PRM)
4. Pulse generator
5. Battery

IMPLANTABLE DEFIBRILLATOR SYSTEM
ARCHITECTURE
AID LEAD
SYSTEM
PULSE GENERATOR
BATTERY

IMPLANTABLE
COMPONENTS
AID
 It houses the power source , sensing, defibrillation,
pacing and telemetric communication system.
 The lead system provides physical and electrical
connection between the defibrillator and the heart tissue.
 The PRM communicates with the AID and allows the
physician to view status information and modify the
function of the device as needed.
Leads
 The defibrillating high energy pulse is delivered to the
heart via 6cm*9cm titanium mesh patch with
electrodes placed directly on the surface of heart.
 Electrode is placed invasively through leads screwed in
the heart.
 Leads are used for defibrillating and sensing.

IMPLANTABLE
COMPONENTS
Programmer Recorder/Monitor (PRM):
 The PRM is an external device that provides a bidirectional communications link to
an implanted AID.
 A telemetry link is established between PRM and AID.
 Telemetry channel is used to retrieve real time and stored intracardiac ECG, therapy
history, battery status and other information.
 It allows the programmer to change the algorithm as per the require for patients
abnormality.
Pulse generator:
 It has a microprocessor which controls overall system functions.
 ROM provides non-volatile memory for system start-up task and some program space
 RAM is required for storage of operating parameters and storage
of
electrocardiogram data.
 System Control supports the circuitry of microprocessor like a telemetry
interface,
typically implemented with a UART-like (universal
asynchronous receiver/transmitter) interface and general purpose timers.

IMPLANTABLE
COMPONENTS
Battery:
 Two connected in series to form approximate 6 V Lithium Silver Vanadium
oxide (LiSVO)
 Separate voltage supplies are generally used for pacing(5V) i.e. low volt
supply and control of the charging circuit (10-15 V) i.e. high volt supply.
 High power circuits convert 3-6V battery voltage to the 750V necessary
for defibrillation.
 DC to DC convertor coverts 6 V battery to 750V, the output storage
capacitor and high output switch are used for defibrillation.
Sense Amplifier
 Proper sensing of heart requires precise sensing and discrimination
of each
of the component to differentiate tachycardia and ventricular
fibrillation.
 It should be able to sense 30 to 360 bpm.
 It should be able to quickly respond to widely varying signals
present during arrhythmia.
 Heat signals lies in the range of 100micoV to 20microV as a result
needs to
amplify to be processed further.

AUTOMATIC OR ADVISORY EXTERNAL
DEFIBRILLATORS
 Smart automatic or advisory external defibrillator (AED) are capable of accurately
analyzing the ECG and making reliable shock decisions.
 The are designed to detect ventricular fibrillation with sensitivity and specificity
comparable to that of well trained paramedics then deliver(automatic) or recommend
(advisory) an appropriate high energy defibrillating shock.
 AED require self adhesive electrodes instead of hand held paddles.
 ECG signal are acquired are faster and more accurate and with less noise and higher
quality.
 Hands-off defibrillation is a safer procedure for the operator especially when operator
has no training.
 Multifunction self adhesive electrodes are commonly used with defibrillator-monitor-
pacer instruments.
 AED has the ability of the device to accurately assess the patient heart and make
therapy decision.
 The defibrillator performs this evaluation by sensing electrical signals from the
patient heart via electrodes and using a computerized algorithm to interpret the
electrical signals.

DC Defibrillator with synchronization

DEFIBRILLATOR
ELECTRODES
 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
 The electrodes for external defibrillation are metal discs about 3-5 cm in
diameter (or rectangular flat paddles 5x10 cm ) and attached to highly insulated
handle.
 The size of electrodes plays an important part in determining the chest wall
impedance which influence the efficiency of defibrillation.
 The capacitor is discharged only when the electrodes make a good and firm
contact with the chest of the patient.
 For internal defibrillation when the chest is open, large spoon- shaped
electrodes are used.
 Self adhesive pre-gelled electrodes :Self-adhering, solid gel construction ensures
easy use with no extra gel needed. Flexible design allows electrodes to better
conform to body contours.

METAL DISC AND SPOON
ELECTRODE

Defibrillator.pptx. Jei3j

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