Defibrillator (ppt)


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  • Explain the cardiac conduction pathways with the electrical impulse originating in the SA node (right atrium) which travels to the AV node (division of the right and left ventricles), down along the right and left bundle branches to the Purkinje fibers.Intrinsic heart rates at the SA node are 80 bpm, the AV node is 60 bpm, and the ventricular rate (Purkinje fibers) is 40 bpm.
  • Defibrillator (ppt)

    1. 1. 1. Define defibrillation. 2. Describe Need and history of defibrillation. 3. Describe the principle and mechanism of defibrillation. 4. Types and classes of defibrillator 5. Describe the Automated external defibrillator 6. Identify the precautions and risk 7. Troubleshooting of defibrillator
    2. 2. Definition: 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. Defibrillation is a common treatment for life threatening cardiac dysrhythmias, ventricular fibrillation, and pulse less ventricular tachycardia.
    3. 3. Ventricular fibrillation is a serious cardiac emergency resulting from asynchronous contraction of the heart muscles.  Due to ventricular fibrillation, there is an irregular rapid heart rhythm. Fig. Ventricular fibrillation Fig. Normal heart beat
    4. 4.  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 instrument for administering the shock is called a DEFIBRILLATOR.
    5. 5. 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.
    6. 6. Defibrillation was invented in by Prevost and Batelli, two Italian physiologists. They discovered that electric shocks could convert ventricular fibrillation to sinus rhythm in dogs.The first case of a human life saved by defibrillation was reported by Beck in 1947 .
    7. 7.  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.
    8. 8. Fig: Schematic diagram of a defibrillator
    9. 9.  The discharge resistance which the patient represents as purely ohmic resistance of 50 to 100Ω approximately for a typical electrode size of 80cm2.  This particular waveform Fig is called „ Lown‟ waveform.  The pulse width of this waveform is generally 10 ms.
    10. 10. current (amps) defibrillation occurs no defibrillation pulse duration
    11. 11. • minimum defibrillation energy occurs for pulse durations of 3 - 10 ms (for most pulse shapes). • pulse amplitude in tens of amperes (few thousand volts).
    12. 12. • 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.)
    13. 13.  Fibrillations cause the heart to stop pumping blood, leading to brain damage.  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.
    14. 14.  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!
    15. 15. Electrical pattern ECG tracing
    16. 16.  Occulsion of the coronary artery leads to ischemia  Ischemia leads to infarct which causes interruption of normal cardiac conduction  Infarct = VF/VT
    17. 17. Ventricular Fibrillation Ventricular Tachycardia
    18. 18.  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
    19. 19. 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.
    20. 20. Fig.- Pad electrode
    21. 21. Anterior electrode pad Apex electrode pad Fig: anterior –apex scheme of electrode placement
    22. 22. Monophasic pulse or waveform Bi-phasic pulse or waveform
    23. 23.  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
    24. 24. Fig:- Generation of bi-phasic waveform
    25. 25.  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.
    26. 26. Internal External 28
    27. 27. Internal defibrillator a) • Electrodes placed directly to the heart • e.g..-Pacemaker b) External defibrillator • Electrodes placed directly on the heart • e.g..-AED
    28. 28. • For each minute elapsing between onset of ventricular fibrillation and first defibrillation, survival decreases by 10%. • defibrillators should be portable, battery operated, small size. • energy in defibrillators usually stored in large capacitors. • total energy stored in capacitor: WC 1 CVC2 2 Vc = capacitor voltage
    29. 29. 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
    30. 30.  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.
    31. 31.  AEDs require self-adhesive electrodes instead of hand held paddles.  The AED uses voice prompts, lights and text tell the rescuer what steps have to take next. messages to
    32. 32.  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 shock able rhythm or not
    33. 33. 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.
    34. 34. The paddles used in the procedure should not be placed:• on a woman's breasts • over an internal pacemaker patients.  Before the paddle is used, a gel must be applied to the patient's skin
    35. 35. • 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.
    36. 36. • 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.
    37. 37. • 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”.
    38. 38.     Willis A Tacker, “External Defibrillators,” in The Biomedical Engineering Handbook, J. Bronzino (ed) CRC Press, 1995.