In The Name of Allah The Most Beneficent The Most Merciful

1. In The Name of Allah The Most Beneficent The Most Merciful

2. ECE 4550:Biomedical Instrumentation Lecture:Defibrillators Engr. Ijlal Haider University of Lahore, Lahore

3. NEED FOR A DEFIBRILLATOR • Ventricular fibrillation is a serious cardiac emergency • resulting from asynchronous contraction of the heart • muscles. • Due to ventricular fibrillation, there is an irregular or • rapid heart rhythm. Fig. Normal heart beat Fig. Ventricular fibrillation

4. NEED FOR A DEFIBRILLATOR • 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 pacemaking pulses. • The instrument for administering the shock is called a • DEFIBRILLATOR.

5. TYPES OF DEFIBRILLATORS Internal External

6. TYPES OF DEFIBRILLATORS • Internal defibrillator • Electrodes placed directly to the heart • Eg.-Pacemaker • External defibrillator • Electrodes placed directly on the heart • Eg.-AED

7. DEFIBRILLATOR ELECTRODES • Types of Defibrillator electrodes:- • Spoon shaped electrode • Applied directly to the heart. • Paddle type electrode • Applied against the chest wall • Pad type electrode • Applied directly on chest wall

8. DEFIBRILLATOR ELECTRODES

9. DEFIBRILLATOR ELECTRODES Fig.- Pad electrode

10. DEFIBRILLATOR ELECTRODES • Electrodes have insulated handles • Designed to prevent the spread of jell from electrodes to handles for the safety and easeof operator

11. PRINCIPLE OF DEFIBRILLATION • 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.

13. PRINCIPLE OF DEFIBRILLATION

14. PRINCIPLE OF DEFIBRILLATION • The discharge resistance which the patient represents as • purely ohmicresistance of 50 to 100Ω approximately for • a typical electrode size of 80cm2. • This particular waveform Fig 13.9(b) is called ‘ Lown’ • waveform. • The pulse width of this waveform is generally 5-10 ms.

16. Peak current of 50 A • Time 5 sec • Resistance 50 ohm • Power delivered = 320 J • To overcome losses across capacitor and inductor • 25% additional energy required • Energy to be stored is 400 J • Capacitor of 16 micro farad • Voltage required is 7000V

17. For Internal electrodes only 50 J is needed

18. Classes of discharge waveform Bi-phasic pulse or waveform Monophasic pulse or waveform

19. Classes of discharge waveform • There are two general classes of waveforms: • mono-phasic waveform • Energy delivered in one direction through the patient’s heart • Biphasic waveform • Energy delivered in both direction throuth the patient’s heart

20. Classes of discharge waveform Fig:- Generation of bi-phasic waveform

21. Classes of discharge waveform • 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 lower-energy shocks • of 120 - 200 joules, with each shock moving in an • opposite polarity between the pads.

22. Classes of discharge waveform • Dual Peak Waveform • 10 msec • Truncated Waveform • Time can be adjusted

23. AUTOMATIC EXTERNAL DEFIBRILLATOR

24. AUTOMATIC EXTERNAL DEFIBRILLATOR • AED is a portable electronic device that automatically • diagnoses the ventricular fibrillation in a patient. • Automatic refers to the ability to autonomously analyse • the patient's condition. • AED is a type of external defibrillation process. • AEDs require self-adhesive electrodes instead of hand • held paddles. • The AED uses voice prompts, lights and text messages to • tell the rescuer what steps have to take next.

25. ELECTRODE PLACEMENT OF AED Anterior electrode pad Apex electrode pad Fig. anterior –apex scheme of electrode placement

26. WORKING OF AED • turned on or opened AED. • 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 shockable • rhythm or not.

27. WORKING OF AED • 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.

28. Courtesy Texas Instruments

29. Testing Defibrillators A dummy load is connected across the defibrillator electrodes Discharge is observed 50 ohm resistance is taken as human resistance connected in series with a low value resistor. Neon light is connectedwith low value resistor and lights when defibrillator is discharged

30. Testing Defibrillators Some defibrillators have built-in testsystem If they do not have, it can be designedand mounted on the trolley

31. Current requirements normally range up to 20 A. • Voltage ranges from 1000V to 6000V • Time of discharge is kept from 5 to 10 msec • Current is dependent on the body (chest) resistance • For reference visit: • http://www.resuscitationcentral.com/defibrillation/biphasic-waveform/ • And various other resources on internet

32. Thank You!