Defibrillation is a process that delivers an electric shock to the heart to stop an irregular heartbeat and restore normal rhythm. It is the only effective treatment for cardiac arrest caused by ventricular fibrillation or pulseless ventricular tachycardia. Early defibrillation is critical, as survival rates decrease by 10% each minute without treatment. Different types of defibrillators include automated external defibrillators and implantable cardioverter defibrillators. Key factors that influence defibrillation success include transthoracic impedance, electrode placement and position, and shock waveform and energy level delivered.

1. DEFIBRILLATION

2. Outline
• Introduction
• History of Defibrillators
• Principles and mechanisms of Defibrillators
• Types and classes of Defibrillators
• Automated external defibrillator
• Procedure for Defibrillation
• Safety precautions during Defibrillation
• Conclusion

3. INTRODUCTION
• Defibrillation is a process in which an electronic device sends an
electric shock to the heart to stop an extremely rapid, irregular
heartbeat and restore the normal heart rhythm.
• Electrical defibrillation is the only effective therapy for cardiac arrest
caused by life threatening cardiac dysrhythmias specifically
ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT).
• The guidelines on cardiopulmonary resuscitation of the European
Resuscitation Council and American Heart Association (AHA) strongly
recommend attempting defibrillation with minimal delay in victims of
VF/VT cardiac arrest.

4. INTRODUCTION cont’d
• If defibrillation is delivered promptly, survival rates increases to as
high as 75%.
• The chances of a favorable outcome decline at a rate of about 10%
for each minute cardiac defibrillation is delayed.
• As this event occurs most often in the victim’s private home or in
public spaces away from healthcare facilities, the need for early
defibrillation has led to the development of automatic, portable
defibrillators.

5. HISTORY
• In Switzerland, 1899, Prevost and Batelli discovered that small electric shocks
could induce ventricular fibrillation in experimental animals and that larger
charges would reverse the condition by using AC and DC shocks.
• Wiggers repeated their work in the 1930s, which then prompted Claude Beck, a
surgeon in Cleveland, to attempt defibrillation in humans who developed VF
while undergoing thoracotomy
• His first success came in 1947 when VF developed in a 14 year old boy whose
chest was being closed after surgery for a funnel chest using a homemade AC
defibrillator, developed by Kouwenhoven, with electrodes placed directly on the
heart

6. HISTORY cont’d
• Kouwenhoven was also instrumental in the development of the
external defibrillator, which was first successfully employed by Paul
Zoll in a patient with recurrent VF and pulseless ventricular
tachycardia complicating sinoatrial disease
• Following this breakthrough, direct current defibrillators were
introduced into clinical practice around 1962 when it was
demonstrated that electrical countershock or cardioversion across the
closed chest could abolish other cardiac arrhythmias in addition to
ventricular fibrillation

7. • The first successful defibrillation outside hospital was reported by
Pantridge in 1967
• Later on, Diack et al. described the first clinical experience with an
AED. Subsequently, further studies provided solid evidence on the
potential role of these devices in the early defibrillation and survival.

8. DEFIBRILLATORS
• Defibrillators are devices that restore a normal heartbeat by sending
an electric pulse or shock to the heart.
• They are used to prevent or correct an arrhythmia. They are also used
to restore the hearts beating if the heart suddenly stops.
• They are performed immediately after identifying that the patient is
experiencing a cardiac emergency, has no pulse and is unresponsive.
• A defibrillator delivers a dose of electric current(often called a
counter-shock) to the heart.

9. DEFIBRILLATORS cont’d
• Defibrillation aims to depolarise most of the myocardium
simultaneously ending the dysrhythmia thereby allowing the natural
pacemaker tissue to resume control of the heart in sinus rhythm
• Depolarisation of a critical mass of myocardium is necessary and this
depends on the transmyocardial current flow (measured in Amperes)
rather than the energy of the delivered shock (measured in Joules).
• A heart which is in asystole(flatline) cannot be restarted by a
defibrillator but would be treated by cardiopulmonary resuscitation

10. DEFRIBILLATORS cont’d
• Different types of defibrillators work in different ways. Automated
external defibrillators(AED) which are in many public spaces were
developed to save lives of people experiencing cardiac arrest. Even
untrained bystanders can use these devices in an emergency.
• Other defibrillators can prevent sudden death among people who
have a high risk of a life-threatening arrhythmia. They include
implantable cardioverter defibrillators(ICD) which are surgically
placed inside your body and wearable cardioverter
defibrillators(WCD) which rest on the body.

11. VENTRICULAR FIBRILLATION
• Ventricular fibrillation (VF) is a serious cardiac emergency resulting
from asynchronous contraction of the heart muscles
• Due to ventricular fibrillation, there is an irregular rapid heart rhythm.
• The heart stops functioning as an effective pump and in the absence
of cardiac output, the myocardium becomes more ischaemic and
irreversible anoxic damage occurs within few minutes

12. VENTRICULAR FIBRILLATION cont’d
• Ventricular fibrillation can be converted into a more efficient rhythm by
applying a high energy shock to the heart.
• This sudden surge across the heart causes all muscle fibres to contract
simultaneously. Possibly the fibres may then respond to normal
physiological pace making pulses
• The probability of successful defribillation and subsequent survival to
hospital discharge is inversely related to the time interval between the
onset of VF and delivery of the first countershock.
• The chances of success declines by about 7-10% for each minute delay in
administering the shock

13. • In VF the electrocardiograph shows a bizarre, irregular waveform that
is apparently random in both frequency and amplitude.
• VF is sometimes classified as either coarse or fine, depending on the
amplitude of the complexes
• VF is the commonest initial rhythm leading to cardiac arrest,
particularly in patients with coronary heart disease.
• VF may be preceded by ventricular tachycardia and is seen in up to
80-90% of those patients dying suddenly outside hospital

15. ECG RHYTHMS- Shockable/ non shockable
VENTRICULAR
TACHYCARDIA
VENTRICULAR
FIBRILLATION
PULSELESS
ELECTRICAL
ACTIVITY
ASYSTOLE

17. Defibrillator shock waveform
• The effectiveness of a shock in terminating VF depends on the type of
shock waveform discharged by the defibrillator.
• Monophasic waveform. Defibrillators with this type of waveform
deliver current in one polarity.
• They can be further categorized by the rate at which the current pulse
decreases to zero.
• If the monophasic waveform falls to zero gradually, the term damped
sinusoidal is used. If the waveform falls instantaneously, the term
truncated exponential

18. • When using a defibrillator with a monomorphic waveform it is
recommended that the first shock should be at an energy level of
200J.
• Should this be unsuccessful, a second shock at the same energy level
may prove effective because the transthoracic impedance is reduced
by repeated shocks.
• If two shocks at 200 J are unsuccessful, the energy setting should be
increased to 360 J for the third and subsequent attempts
• It gives up to 360 to 400 joules due to which cardiac injury and burns
around the shock pad sites is increased

19. Defibrillator waveforms
8/20/2023 4:22 PM PRIMARY FMCP UPDATE - CPR LECTURE 19
Damped Monophasic Truncated Biphasic

20. • Biphasic waveform. This type of waveform was developed later. The
delivered current flows in a positive direction for a specified time and
then reverses and flows in a negative direction for the remaining
duration of the electrical discharge
• With biphasic waveforms there is a lower defibrillation threshold
(DFT) that allows reductions of the energy levels administrated and
may cause less myocardial damage.
• It delivers two sequential lower energy shocks of 120-200joules

21. • A biphasic shock of 150J is commonly considered to be at least as
effective as a 200J monophasic shock.
• Defibrillators that deliver biphasic shocks are now in clinical use, and
considerable savings in size and weight result from the reduced
energy levels needed.
• Biphasic shocks have been widely employed in implantable
cardioverter defibrillators (ICDs) because their increased effectiveness
allows more shocks to be given for any particular battery size

23. FACTORS AFFECTING A DEFRIBILLATOR
• Transmyocardial current flow
• Most defibrillators are energy-based, meaning that the device charges a capacitor
to a selected voltage and then delivers a pre-specified amount of energy in
joules.
• The amount of energy which arrives at the myocardium is dependent on the
selected voltage and the transthoracic impedance that is, the resistance to
current flow through the chest wall, lungs, and myocardium (which varies by
patient).
• The optimal shock energy is one that will achieve defibrillation successfully while
causing minimal electrical injury to the myocardium.
• Achieving an appropriate current flow will reduce the number of shocks required
and may limit further myocardial damage.

24. • Determinants of current flow
 Energy of delivered shock
Transthoracic impedance
Electrode position
Shock waveform
Body size
Electrode size

25. • Transthoracic impedance
• In adults transthoracic impedance averages about 60Ohms, with 95%
of the population lying in the range of 30-90Ohms.
• Current flow will be highest when transthoracic impedance is at its
lowest.
• To achieve this the operator should press firmly when using handheld
electrode paddles. A conductive electrode gel or defibrillator pads
should be used to reduce the impedance at the electrode and skin
interface. Self-adhesive monitor or defibrillator electrodes do not
require additional pressure.

26. • In patients with considerable chest hair, poor electrode contact and
air trapping will increase the impedance. This can be avoided by
rapidly shaving the chest in the areas where the electrodes are
placed.
• Transthoracic impedance is about 9% lower when the lungs are
empty, so defibrillation is best carried out during the expiratory phase
of ventilation
• It is also important to avoid positioning the electrodes over the
breast tissue of female patients because this causes high impedance
to current flow.

27. • Determinants of transthoracic impedance
 Shock energy
 Electrode size
Electrical contact
Number of and time since previous shocks
Phase of ventilation
Distance between electrodes
 Paddle or electrode pressure

28. Electrode position
• The ideal electrode position allows maximum current to flow through the
myocardium.
• This will occur when the heart lies in the direct path of the current
• The standard position consists of one electrode placed to the right of the
upper sternum below the right clavicle(anterio-lateral) and the other
placed in the mid-axillary line at the level of the fifth left intercostal
space(anterio-posterior)
• An alternative is to place one electrode to the left of the lower sternal
border(anterior left infrascapular) and the other on the posterior chest wall
below the angle of the left scapula(anterior right infrascapular)
• Avoid placing electrodes directly over breast tissue in women

30. • Electrode size or surface area
 Low transthoracic impedence is achieved with larger electrodes.
Above an optimum size the transmyocardial current will be reduced
The usual electrode sizes employed are 10-13cm in diameter for
adults and 4.5-8cm for infants and children
• Body size
 Infants and children require shocks of lower energy than adults to
achieve defibrillation
 Over the usual range of weight encountered in adults, body size does
not greatly influence the energy requirements

31. TYPES OF DEFRIBILLATORS
• Manual defibillators; external manual and internal manual
defibrillators
• Automated defibrillators; external or internal automated defibrillators
Internal defribillator. Electrodes are placed directly to the heart
External defribillator. Electrodes placed directly on the heart

33. • Other types of defibrillators less frequently used in clinical practice:
Impedance-based defibrillators allow selection of the current
applied based upon the transthoracic impedance (TTI). TTI is assessed
initially with a test pulse and subsequently the capacitor charges to
the appropriate voltage.
Current-based defibrillators deliver a fixed dose of current which
results in defibrillation thresholds that are independent of TTI . The
optimal current for ventricular defibrillation appears to be 30 to 40
amperes independently of both TTI and body weight thus achieving
defibrillation with considerably less energy than the conventional
energy-based method

34. Cardioversion
• Cardioversion is one of the possible treatments for arrhythmias that
imply a re-entrant circuit.
• By delivering a synchronized electric shock all excitable tissue of the
circuit is simultaneously depolarised making the tissue refractory and
the circuit no longer able to sustain re-entry.
• As a result, cardioversion terminates arrhythmias resulting from a
single reentrant circuit, such as atrial flutter, atrioventricular nodal
reentrant tachycardia or monomorphic ventricular tachycardia.

35. • Current European Society of Cardiology and AHA guidelines suggest the
following initial energy selection for specific arrhythmias
• For atrial fibrillation, 120 to 200 joules for biphasic devices and 200 joules
for monophasic devices.
• For atrial flutter, 50 to 100 joules for biphasic devices and 100 joules for
monophasic devices.
• For ventricular tachycardia with a pulse, 100 joules for biphasic devices and
200 joules for monophasic devices.
• For ventricular fibrillation or pulseless ventricular tachycardia, at least 150
joules for biphasic devices and 360 joules for monophasic devices.

36. Procedure for defibrillation

37. Automated external defibrillator
• The term refers to a portable and lightweight computerized device that
incorporates rhythm analysis and defibrillation systems and uses voice
and/or visual prompts to guide lay rescuers and healthcare providers to
safely defibrillate victims of cardiac arrest due to VF or pulseless VT.
• There are two types of AED: the semi-automatic that indicates the need for
defibrillation but requires that the operator deliver the shock by pushing a
button and the fully automatic AED which is capable of administering a
shock without the need for outside interventions.
• Basically these devices consist of a battery, a capacitor, electrodes and an
electrical circuit designed to analyze the rhythm and send an electric shock
if is needed.

38. Components of an AED
Basically these devices consist of a battery, a capacitor,
electrodes and an electrical circuit designed to analyze
the rhythm and send an electric shock if is needed

39. • Batteries. Essentially they are containers of chemical reactions and
one of the most important parts of the AED system.
• Initially lead batteries and nickel-cadmium were used but lately non-
rechargeable lithium batteries, smaller in size and with longer
duration without maintenance (up to 5 years), are rapidly replacing
them.
• Since extreme temperatures negatively affect the batteries,
defibrillators must be stored in controlled environments

40. • Capacitor. The electrical shock delivered to the patient is generated
by high voltage circuits from energy stored in a capacitor which can
hold up to 7 kV of electricity.
• The energy delivered by this system can be anywhere from 30 to 400
joules.
• Electrodes are the components through which the defibrillator
collects information for rhythm analysis and delivers energy to the
patient's heart.
• Many types of electrodes are available including hand-held paddles,
internal paddles, and self-adhesive disposable electrodes.

41. • Electrical circuit. AEDs are highly sophisticated, microprocessor-based
devices that analyze multiple features of the surface ECG signal
• Controls. The typical controls on an AED include a power button, a
display screen on which trained rescuers can check the heart rhythm
and a discharge button.
• Defibrillators that can be operated manually have also an energy
select control and a charge button including frequency, amplitude,
slope and wave morphology

42. Semi-automatic AEDs Fully automatic AED
Definition Indicates the need for defibrillation
but requires an operator to deliver
the shock by pushing a button
Capable of administering a shock
without the need for outside
interventions
Advantages • Recommended by current
resuscitation guidelines
• Widely used
• Allows healthcare professionals
to override the device and deliver a
shock manually, independently of
prompts.
• Safer, no risk of inappropriate
shocks to the rescuer
• Easier to use and more
appropriate for lay-rescuers
• Better compliance with
resuscitation protocols
Disadvantages • More complex to use for the
untrained responders
• More difficult to synchronize with
CPR maneuvers for lay rescuers
• Longer times until shock delivery
• Risk of electrocution for the
rescuer if inappropriately used
• No possibility to override the
device
• Not recommended by current

43. Semi-automatic AEDs Fully automatic AED
Definition
Indicates the need for defibrillation but requires an operator to
deliver the shock by pushing a button
Capable of administering a shock without the need for outside interventions
Advantages
• Recommended by current resuscitation guidelines
• Widely used
• Allows healthcare professionals to override the device and deliver a
shock manually, independently of prompts.
• Safer, no risk of inappropriate shocks to the rescuer
• Easier to use and more appropriate for lay-rescuers
• Better compliance with resuscitation protocols
Disadvantages
• More complex to use for the untrained responders
• More difficult to synchronize with CPR maneuvers for lay rescuers
• Longer times until shock delivery
• Risk of electrocution for the rescuer if inappropriately used
• No possibility to override the device
• Not recommended by current guidelines except for special situations

44. Sequence of action for AED
• Once cardiac arrest has been confirmed it may be necessary for an
assistant to perform basic life support while the equipment is
prepared and the adhesive electrodes are attached to the patient’s
chest
• Once the AED is ready to use, the following sequence should be used:

46. • Repeat as directed for up to three shocks in any one sequence. Do not
check for a pulse or other signs of a circulation between the three
shocks.
• If no pulse or other sign of a circulation is found, perform CPR for one
minute. This will be timed by the machine, after which it will prompt
the operator to reanalyse the rhythm.
• Alternatively, this procedure may start automatically, depending on
the machine’s individual features or settings. Shocks should be
repeated as indicated by the AED.

47. • If a circulation returns after a shock, check for breathing and
continue to support the patient by rescue breathing if required.
• Check the patient every minute to ensure that signs of a circulation
are still present.
• If the patient shows signs of recovery, place in the recovery position.

48. • Safety factors
• All removable metal objects, such as chains and medallions, should
be removed from the shock pathway—that is, from the front of the
chest.
• Body jewellery that cannot be removed will need to be left in place.
Although this may cause some minor skin burns in the immediate
area, this risk has to be balanced against the delay involved in its
removal
• Clothing should be open or cut to allow access to the patient’s bare
frontal chest area

49. • The patient’s chest should be checked for the presence of self-
medication patches on the front of the chest (these may deflect
energy away from the heart)
• Oxygen that is being used—for example, with a pocket mask—should
be directed away from the patient or turned off during defibrillation
• The environment should be checked for pools of water or metal
surfaces that connect the patient to the operator. It is important to
recognise that volatile atmospheres, such as petrol or aviation fumes,
can ignite with a spark

50. Wearable cardioverter defibrillator(WCD)
• The concept of WCD consists of longterm monitoring, detection of sudden
cardiac death and shock delivery without bystander assistance or an
implanted device to bridge an assessment period or to let optimal medical
therapy deliver its benefits
• The sensing and therapy delivery component consists of 1 anterior and 2
posterior self gelling defibrillation electrodes held together by an elastic
chest garment
• Dry tantalum oxide electrodes provide long term ECG monitoring through 2
non-standard leads (anteroposterior and left-right bipolar signals) whereas
the defibrillation electrodes contain a vibration plate and multiple gel
capsules. The vibration plate is intended to give the patient a tactile
warning of an impending shock once a shockable rhythm detection occurs

51. • The defibrillation gel is released to minimize skin-pad impedance and
prevent skin injury during shock delivery
• When the patient receives tactile, audible and visual alerts, the
therapeutic shock can be aborted by simultaneously pressing 2
buttons
• The WCD is able to deliver shock up to 150j, biphasic with a
programmable response time of 25-180s
• Reported rates of inappropriate therapies range from 0.4-0.5 with fast
supraventricular tachycardia and artifacts as the most common
underlying cause

52. • WCD can be considered in adult patients who present a high
arrhythmic risk for a limited period of time such as reduced LVEF, as a
bridge to heart transplantation or left ventricular assist devices, in the
40days after myocardial infarction or in the 3months after a coronary
artery bypass graft
• WCD can be considered when a transient contraindication to icd is
present such as endocarditis or device related infection

53. Conclusion
• Sudden cardiac arrest, frequently due to VF or pulseless VT, is
traditionally associated with poor survival rates.
• Saving the lives of these patients depends on early cardiac
defibrillation which, with manual defibrillators, is limited only to
qualified rescuers who can interpret ECGs.
• AEDs solve this problem since they are able to analyze rhythm and
inform the rescuers whether a shock is indicated

54. • This approach allows lay rescuers to provide effective early
defibrillation which has been shown to significantly improve survival
and survival with intact neurologic function after out-of-hospital
cardiac arrest.
• One limitation is that AED use requires interruptions in CPR which
was proved to be deleterious especially in patients with non-
shockable rhythms.
• Special efforts are being made in order to improve rhythm analysis
and ‘hands-off’ time during CPR.