Defibrillator is a device that deliver a therapeutic

�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 more normal cardiac rhythm.

Defibrillation is a common treatment for life threatening cardiac dysrhythmias, ventricular fibrillation, and pulse less ventricular tachycardia.

v. Ventricular fibrillation is a serious cardiac emergency resulting from asynchronous contraction of the heart muscles. v Due to ventricular fibrillation, there is an irregular rapid heart rhythm. Fig. Ventricular fibrillation Fig. Normal heart beat

v Ventricular fibrillation can be converted into a more efficient rhythm by applying a high energy shock to the heart. v This sudden surge across the heart causes all muscle fibres to contract simultaneously. v Possibly, the fibres may then respond to normal physiological pace making pulses. v The instrument for administering the shock is called a DEFIBRILLATOR.

Defibrillation is performed to correct lifethreatening fibrillations of the heart, which could result in cardiac arrest. It should be performed immediately after identifying that the patient is experiencing a cardiac emergency, has no pulse, and is unresponsive.

v Energy storage capacitor is charged at relatively slow rate from AC line. v Energy stored in capacitor is then delivered at a relatively rapid rate to chest of the patient. v Simple arrangement involve the discharge of capacitor energy through the patient’s own resistance.

AC DEFIBRILLATION § Applying a brief(. 25 to 1 sec) burst of 50 HZ ac at an intensity of around 6 A. § This application of an electrical shock to resynchronize the heart is sometimes called counter shock. § If the patient does not respond, the burst is repeated until defibrillation occurs. this method is known as ac defibrillation.

Disadvantage of using ac Defibrillator �It is cannot be successfully used to correct atrial fibrillation. � Successive attempts to correct ventricular fibrillation are often required. �Attempts to correct atrial fibrillation by this method often result more serious ventricular fibrillation.

DC Defibrillation Ø In this method a capacitor is charged to a high dc voltage and then rapidly discharged. Ø The amount of energy discharged by the capacitor may range between 2 to 400 joules with peak value of current 20 A. Ø A corrective shock of 750 -800 volts is applied within a tenth of a second.

CIRCUIT OF DC DEFIBRILLATOR

PRINCIPLE OF DEFIBRILLATOR �Energy storage capacitor is charged at relatively slow rate from AC line. �Energy stored in capacitor is then delivered at a relatively rapid rate to chest of the patient. �Simple arrangement involve the discharge of capacitor energy through the patient’s own resistance.

Cont…. . The discharge resistance which the patient represents is roughly a ohmic resistance of 50 – 100 ohms for a typical electrode size of 80 cm 2. The particular wave form is called “Lown” wave form. The pulse width of this waveform is 10 ms.

Electrodes placed directly around the heart area of chest. Higher Voltage required than internal defibrillator. Classified as Monophasic Biphasic

Monophasic waveform Defibrillators �Deliver current of one polarity. �Current travels in one direction through the patients heart from one paddle to another. 2 types : �The monophasic damped sinusoidal waveform (MDS) returns to zero gradually �Monophasic truncated exponential waveform (MTE) current is abruptly returned to baseline (truncated) to zero current flow

MDS v/s MTE wave form

Defibrillators Current travels towards the +ve paddle & then reverses back. Reversing of polarity, depolarizes all cells – called “burping” response. Classified into – Biphasic truncated exponential waveform (BTE) Rectilinear biphasic waveform (RLB) RLB is better than BTE.

(BTE) v/s Rectilinear biphasic waveform (RLB) RBL BTE

Advantages of Biphasic over Monophasic Less power – Less trauma – Less battery. Defibrillation more effective at low energy. Fewer burns. Less myocardial damage. 1 st shock success rate in cardiac arrest due to shockable rhythm – Monophasic 60% Biphasic increases to 90%

Types of Defibrillators 1. Manual external defibrillator 2. Manual internal defibrillator 3. Semi-Automated External Defibrillator 4. Automated external defibrillator (AED) 5. Implantable cardioverter-defibrillator (ICD) {automatic internal cardiac defibrillator (AICD)} 6. Wearable cardiac defibrillator

Fig: Schematic diagram of a defibrillator

v The discharge resistance which the patient represents as purely ohmic resistance of 50 to 100Ω approximately for a typical electrode size of 80 cm 2. v This particular waveform Fig is called ‘ Lown’ waveform. v The pulse width of this waveform is generally 10 ms.

s) ule o j ( y rg current (amps) ene e( s) b m o coul g char pulse duration defibrillation occurs no defibrillation

• minimum defibrillation energy occurs for pulse durations of 3 - 10 ms (for most pulse shapes). • pulse amplitude in tens of amperes (few thousand volts).

• operator selects energy delivered: 50 -360 joules, depends on: – intrinsic characteristics of patient – patient’s disease – duration of arrhythmia – patient’s age – type of arrhythmia (more energy required for v. fib. )

v Fibrillations cause the heart to stop pumping blood, leading to brain damage. v Defibrillators deliver a brief electric shock to the heart, which enables the heart's natural pacemaker to regain control and establish a normal heart rhythm.

�Higher voltages are required for external defibrillation than for internal defibrillation. �A corrective shock of 750 -800 volts is applied within a tenth of a second. �That is the same voltage as 500 -533 no of AA batteries!

Electrical pattern ECG tracing

�Occulsion of the coronary artery leads to ischemia �Ischemia leads to infarct which causes interruption of normal cardiac conduction �Infarct = VF/VT

Ventricular Fibrillation Ventricular Tachycardia

v 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

fig: Electrodes used in defibrillator (a) a spoon shaped internal electrode that is applied directly to the heart. (b) a paddle type electrode applied against the anterior chest wall.

Fig. - Pad electrode

Anterior electrode pad Apex electrode pad Fig: anterior –apex scheme of electrode placement

Monophasic pulse or waveform Bi-phasic pulse or waveform

v There are two general classes of waveforms: a) mono-phasic waveform • Energy delivered in one direction through the patient’s heart a) Biphasic waveform • Energy delivered in both direction through the patient’s heart

Fig: - Generation of bi-phasic waveform

v The biphasic waveform is preferred over monophasic waveform to defibrillate. Why? ? ? • A monophasic type, give a high-energy shock, up to 360 to 400 joules due to which increased cardiac injury and in burns the chest around the shock pad sites. • A biphasic type, give two sequential lowerenergy shocks of 120 - 200 joules, with each shock moving in an opposite polarity between the pads.

Internal External 40

a) Internal defibrillator • Electrodes placed directly to the heart • e. g. . -Pacemaker b) External defibrillator • Electrodes placed directly on the heart • e. g. . -AED

• F o r e a c h m i n u Vc = capacitor voltage

standby power supply charge discharge gate patient switch is under operator control energy storage timing circuitry applies shock about 20 ms after QRS complex, avoids T-wave ECG monitor

v AED is a portable electronic device that automatically diagnoses the ventricular fibrillation in a patient. v. Automatic refers to the ability to autonomously analyse the patient's condition. v AED is a type of external defibrillation process.

v AEDs require self-adhesive electrodes instead of hand held paddles. v The AED uses voice prompts, lights and text tell the rescuer what steps have to take next. messages to

v Turned on or opened AED. v AED will instruct the user to: • Connect the electrodes (pads) to the patient. • Avoid touching the patient to avoid false readings by the unit. • The AED examine the electrical output from the heart and determine the patient is in a shock able rhythm or not

§When device determined that shock is warranted, it will charge its internal capacitor in preparation to deliver the shock. § When charged, the device instructs the user to ensure no one is touching the victim and then to press a red button to deliver the shock. § Many AED units have an 'event memory' which store the ECG of the patient along with details of the time the unit was activated and the number and strength of any shocks delivered.

ØThe paddles used in the procedure should not be placed: • on a woman's breasts • over an internal pacemaker patients. Ø Before the paddle is used, a gel must be applied to the patient's skin

• Skin burns from the defibrillator paddles are the most common complication of defibrillation. • Other risks include injury to the heart muscle, abnormal heart rhythms, and blood clots.

• Attach the external and internal paddles if the monitor reads, "No paddles. " • Check to ensure that the leads are securely attached if the monitor reads, "No leads. “ • Connect the unit to AC power if the message reads, "Low battery. " • Verify that the Energy Select control settings are correct if the defibrillator does not charge.

• Change the electrodes and make sure that the electrodes adapter cable is properly connected if you receive a message of "PACER FAILURE. " Restart the pacer. • Close the recorder door and the paper roll if the monitor message reads, "Check recorder”.