DEFIBRILLATOR Defibrillator is a device that deliver a

DEFIBRILLATOR

�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.

DEFIBRILLATOR

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

Arrhythmias Bradycardia Ventricular Tachycardia

NEED FOR A DEFIBRILLATOR 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

NEED FOR A DEFIBRILLATOR 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 DEFIBRILLATOR.

PURPOUSE OF DEFIBILLATION 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.

PRINCIPLE OF DEFIBRILLATION 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.

EXTERNAL DEFIBRILLATOR 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

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 ØIn this method a capacitor is charged to a high dc voltage and then rapidly discharged. ØThe amount of energy discharged by the capacitor may range between 2 to 400 joules with peak value of current 20 A. ØA corrective shock of 750 -800 volts is

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. 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 (RBL) RBL is better than BTE.

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

Fig: - Generation of bi-phasic waveform

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

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. )

�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!

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. - Pad electrode

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

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

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