Chapter 2- Defibrillator.pptx...........

History
1849: Ludwigg and Hoffa – VF induced by electrical
stimuli

History
1899: Prevost and Batelli - while a weak stimulus can
produce fibrillation, a stimulus of higher strength
applied to the heart could arrest ventricular fibrillation
and restore normal sinus rhythm.

History
1947: First defibrillation on humans

History
1966: Belfast Ambulance transported physicians
performed first pre-hospital defibrillation.
1969: First pre-hospital defibrillation by non physicians.
1970’s: Diack, Wellborn and Rullman developed first
automated external defibrillator AED’s.

Chain of Survival
Early Recognition and Assessment
• Early Access
• Early CPR
• Early Defibrillation
• Early Advanced Cardiac Life Support

8
Ventricular Fibrillation (VF)
•The ventricles Move in a fast and disorganized way instead of contracting normally.
•No blood is pumped out of the heart → this causes cardiac arrest.
•⚠️Medical emergency — needs CPR and defibrillation (electric shock) immediately.
No identifiable P waves,
QRS complexes, or T waves
Rate 150 to 500 per minute

9
Ventricular Tachycardia (VT)
•The heart beats very fast (usually >180 beats per minute), but the rhythm is still organized.
•Shows wide and regular QRS complexes (each heartbeat is wide and abnormal).
•Blood still flows, but not effectively.
•If not treated, it can turn into ventricular fibrillation.

10
Tachyarrhythmia
A
B
A tachyarrhythmia is any
abnormally fast heart rhythm
caused by a problem in the
heart’s electrical system.
It combines two ideas:
•“Tachy” = fast
•“Arrhythmia” = irregular or
abnormal rhythm
So, tachyarrhythmia = a fast
and abnormal heart rhythm.

11
Sinus bradycardia
Sinus bradycardia is a slow but regular heart rhythm that starts from the sinus node
“Sinus” → means the rhythm comes from the sinus node (normal origin).
•“Bradycardia” → means slow heart rate (less than 60 beats per minute).
So, sinus bradycardia = normal rhythm, just slower than usual.

Introduction
02/03/2026 MEDICAL INSTRUMENTATION 12

13
DEFIBRILLATORS
Cardiac fibrillation is a condition where in the
individual myocardial cells contract asynchronously
with only very local patterns relating to the
contraction of one cell and that of the next. This
serious condition reduces the cardiac output to near
zero, and it must be corrected as soon as possible
to avoid damage to the patient and death. Electric
shock to the heart can be used to reestablish a more
normal cardiac rhythm. Electric machines that
produce the energy to carry out this function are
known as defibrillators.

Cardiac Fibrillation

Why Cardiac Defibrillation?

Cardiac Arrest
 Occulsion of the
coronary artery leads to
reduced blood flow
 reduced blood flow
leads to infarct which
causes interruption of
normal cardiac
conduction
 Infarct = VF/VT

Shockable Rhythms
Ventricular Fibrillation Ventricular Tachycardia
Sinoatrial (SA) Node
Atrioventricular (AV)
Node

What is cardiac defibrillator

How to use?

What is defibrillator

So Defibrillation

Defibrillator

The longer the duration of fibrillation, the greater the deterioration
of the myocardium, because a fibrillating heart consumes a very large
amount of oxygen.
Defibrillators deliver a brief electric shock to the heart, which enables
the heart's natural pacemaker to regain control and establish a normal
sinus rhythm .
Need a Defibrillator

Types of defibrillators
Manual external defibrillator
Automated external defibrillator (AED)
Implantable cardiac defibrillator (ICD)

Manual external defibrillator
DC defibrillator
Clinician decides what charge
has to be set, depending on
prior knowledge and experience
Shock will be delivered through
paddles applied to the patient’s
chest.
Found in hospitals &
ambulances

Automated external
defibrillator
A unit based on computer technology and designed to analyze the
heart rhythm itself, and then advise whether a shock is required or
not.
 Designed to be used by lay persons, who require little training.
 Usually limited in the treatment of VF and VT rhythms.
Usually take time ( around 5-10 secs) in diagnosing the rhythm
Can be found in places like corporate and government offices,
shopping centers, airports, restaurants, sports stadiums, schools and
universities, community centers, fitness centers and health clubs.

Automated external
defibrillator
Require self-adhesive
electrodes(pads) instead of
handheld paddles
The ECG signal acquired from
self-adhesive electrodes usually
contains less noise and has higher
quality allows faster and more
⇒
accurate analysis of the ECG
better shock decisions
⇒
“Hands off” defibrillation - safer
procedure for the operator,
especially if the operator has little
or no training

Implantable cardiac
defibrillator
An electronic device that constantly monitors heart rate and rhythm.
When it detects a very fast, abnormal rhythm, it delivers energy to the
heart muscle. This causes the heart to beat in a normal rhythm again.
Used for cardioversion, defibrillation, anti-tachycardia pacing &
bradycardia pacing.
2 parts :
a)The leads
b)The pulse generator

What are fibrillator
components?

How does it work?
Electronic counter-shock between to paddles or pads
Depolarises all cardiac cells and interrupts arrhythmia
Allows Sinoatrial (SA) node to recommence its
dominant role
Defibrillation is the most time critical intervention in a patient with a
shockable rhythms

How does it work?
Thoracic Impedance
Impedance is the natural resistance to the flow of
electrical current, measured in Ohms.
Impedance is determined by a number of factors, such
as:
◦ Underlying structures and pathology
◦ Paddle or adhesive pad position

How does it work?
Monophasic Defibrillation
Delivers ‘shock’ in one phase
Adult: 200J, 300J, 360J, all subsequent shocks at 360J
Child: 2J/Kg, 2J/Kg, 4J/Kg, all subsequent shocks at 4J/Kg

How does it work?
Biphasic Defibrillation
Two phases to the delivery of the ‘shock’
Adjusts ‘shock’ according to thoracic impedance
Adult: 150J, 150J, 150J
Child: 1– 2J/Kg

How does it work?
Monophasic v Biphasic Defibrillation
Peak current decreased resulting in less myocardial
damage

Simplifying electricity

Defibrillator

Electronics of the defibrillator

Power supply/ Voltage source
Step-up transformers are transformers that increase voltage
Allow the doctor to choose among different amounts of charge
This output voltage is then fed to a capacitor, which stores the
high voltage charge.
As an additional energy source, many defibrillators also have internal
rechargeable batteries.

Capacitors
Capacitors store a large amount of energy in the form of
electric charge
This stored energy is released over a short period of time
“Capacitance” describes a capacitor quantitatively
C = Q/V
A capacitor has 1 farad of capacitance if a potential difference of 1 volt
is present across its plates, when they hold a charge of 1 coulomb.
Capacitors typically have values of microfarads

Capacitors
Capacitance is directly proportional to area and indirectly proportional to the
distance between plates

Inductors
Coils of wire that produce a magnetic field
when current flows through them, prolong the
duration of current flow
Inductors generate electricity that opposes the
motion of current passing through it
This opposition is called “inductance (L)”.
 Inductors typically have values of microhenries
(µH).

(a) Basic circuit diagram for a capacitive–discharge type of cardiac defibrillator. (b) A
typical waveform of the discharge pulse. The actual wave shape is strongly dependent
on the values of L, C, and the torso resistance RL.

48
Defibrillators
With a circuit such as this, 50 to 100 J (W.s) is required for defibrillation,
using electrodes applied directly to the heart. When external electrodes
are used, energies as high as 400 J may be required.
The energy stored in the capacitor is given by the well-known equation
where C is the capacitance and is the voltage to which the capacitor
is charged. Capacitors used in defibrillators range from 10 to 50 μF
in capacitance. Thus we see that the voltage for a maximal energy of
400 J ranges from 2 to 9 KV, depending on the size of the capacitor.
2
2

C
E 


Defibrillator electrodes
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.

Defibrillator electrodes
For internal defibrillation
when the chest is open,
large spoon- shaped
electrodes are used.

Electrodes used in cardiac defibrillation
(a) A spoon-shaped internal electrode that is applied directly to the heart.
(b) A paddle-type electrode that is applied against the anterior chest wall.
Excellent contact: pulse reaches the heart=firmly placed against the patient
Well insulated =Safe to use

Defibrillator mechanism

Annex timing circuitry

Theory behind
defibrillator

Defibrillator Safety

Synchronization

Bloc diagram of a
defibrillator

Benchmark

After defibrillation

CARDIOVERTER
1.The Problem: A patient has a fast heart rhythm caused by a problem in
the upper chambers (atria). A controlled electric shock can fix this.
2.The Danger: The heart's lower chambers (ventricles) have a brief, vulnerable
period during their resetting phase (represented by the T-wave on an ECG). If a
shock is delivered during this T-wave, it can throw the ventricles into a deadly,
chaotic rhythm (ventricular fibrillation).
3.The Solution: A synchronized defibrillator (cardioveter) is used. It has a
special safety circuit that:
1. Monitors the patient's heartbeat.
2. Identifies the safe, contracting phase of the ventricles (represented by
the R-wave on an ECG).
3. Forces the shock to be delivered only during this safe R-wave,
ensuring it occurs well before the dangerous T-wave and preventing
ventricular fibrillation.

Cardioversion
• Cardioversion is the medical procedure (the action).
• Cardioverter is the device used to perform that procedure.

The implantable cardioverter-
defibrillator

A cardioverter The defibrillation pulse in this case must be synchronized with the R
wave of the ECG so that it is applied to a patient shortly after the occurrence of the R
wave.

74
Cardioverters
The signal from the electrodes passes through a
switch that is normally closed. The operator can
observe the patient’s ECG to see whether the
cardio version was successful. The output is
also filtered and passed through a threshold
detector that detects the R wave. This activates
a delay circuit that delays the signal by 30 ms
and then activates a trigger circuit that opens the
switch connecting the ECG electrodes to the
amplifier. At the same time, it closes a switch
that discharges the defibrillator capacitor.

75
Defibrillator Vs. Cardioverter
Defibrillation Cardioversion

76
Defibrillator Vs. Cardioverter

Defibrillator maintenance
policy
First, The daily test procedure - 30 J self test
‑ : is a low energy
test to check the charging circuits & the integrity of cables.
Second, a weekly check - is carried out to test at higher energy
level using ECG simulator.
Third, the detailed half yearly test procedure-
‑ should be
performed by the biomedical department in a hospital

Daily low energy test
Step 1 : Put the defibrillator on Battery mode and ensure
machine
is disconnected from the AC power supply .
Turn the selector switch to ON and select Manual mode
Select leads to PADDLES/PADS
Step 2 : Ensure the universal cable is connected to the paddles
Place paddles in paddle wells
Step 3 : Select the ENERGY to 30 J
Step 4 : Press the CHARGE button
Step 5 : The unit charges to 30J, then the red LED charge
indicator illuminates and the charge tone sounds

Step 6 : Ensure DEFIB 30J READY displays on screen
Step 7 : Press and hold both paddles SHOCK buttons
Step 8 : The unit discharges. The TEST OK message displays and
the red LED turns off
Step 9 : The above TEST OK message conforms that low energy
circuits are in proper working condition

Weekly test: Defibrillator
internal discharge test
Repeat the steps from 1 to 9
Step 10 : Select ENERGY button to maximum energy level 200J displays
Step 11 : The unit charges to 200J, then the red LED charge indicator
illuminates and the charge tone sounds
Step 12 : Ensure DEFIB 200J READY displays on screen
Step 13 : Ensure the machine holds the charge for 50 seconds by giving a long
continuous sound
Step 14 : This confirms the unit is fully functional

1) Duration of VF
- the longer VF lasts, the harder it is to cure
- the quicker the better
- shock early, shock often
- likelihood of resuscitation decrease by 7-10% with every
passing minute (Ann Emerg Med. 1993;22:1652–1658 )
Factors to consider during defibrillation

2) Myocardial environment / condition
Hypoxia, acidosis, hypothermia, electrolyte imbalance,
drug toxicity – impede conversion.
DO NOT DELAY SHOCK trying to correct these problems.

3) Heart size / Body type
Pediatric requirement lower than adult
2J /kg initial shock
4J /kg repeat shock
Higher dose (up to 10J/kg)
Or adult maximum dose
Direct size / energy relationship in adults unknown

4) Use largest size paddles
- completely contact chest without paddles touching each
other
- In pediatric minimum of 3cm distance between pads.
NOTE :-
- Small paddles : concentrate current, burn heart.
- Large paddles : reduces current density

5) Previous counter shock
- repeated shocks lower resistance
- give one shock at a time & then continue CPR
- subesquent shock either equal or higher energy
6) Paddle size
( as discussed before)

7) Paddle placement
- In pacemaker / ICD
at least 12cm from generator
90 degree toAICD electrode
avoid placing pads directly over
no delay in defibrillation
- for other as described before…….

8) Paddles – Skin interface
- only gel should be used (ECG gelly)
- cream, paste, saline pads etc.- not recommended
- gel decreases resistance to the flow of current
- never use alcohol
9) Paddle contact pressure
- firm pressure of 25 pounds
- in child <10kgs --- 3kg pressure
- in large children >10kgs --- 5kg pressure
- deflate lung, shortens the path of current
- do not lean on paddles : they slip

Thank you!!

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