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2. defibrillators
- 1. 2/14/2014 1 DEFIBRILLATOR BY M. WASIM MUNIR Bio-Instrumentation I Defibrillation 2 Defibrillation is based upon the understanding that contraction of the heart and the resulting circulation is under the control of the electrical conduction system of the heart Defibrillation is a common treatment for life- threatening cardiac dysrhythmias, ventricular fibrillation and ventricular tachycardia Defibrillation consists of delivering a therapeutic dose of electrical energy to the affected heart with a device called a defibrillator Department of Biomedical Engineering, SSUET
- 2. 2/14/2014 2 NEED FOR A DEFIBRILLATOR 3 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 Department of Biomedical Engineering, SSUET NEED FOR A DEFIBRILLATOR 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 pacemaker pulses The instrument for administering the shock is called a DEFIBRILLATOR Department of Biomedical Engineering, SSUET
- 3. 2/14/2014 3 5 Department of Biomedical Engineering, SSUET TYPES OF DEFIBRILLATORS Department of Biomedical Engineering, SSUET 6 Internal External
- 4. 2/14/2014 4 TYPES OF DEFIBRILLATORS a)Internal defibrillator •Electrodes placed directly to the heart •E.g. -Implantable CardioverterDefibrillator (ICD) b)External defibrillator •Electrodes placed directly on the heart •E.g. -Automated External Defibrillator (AED) 7 Department of Biomedical Engineering, SSUET DEFIBRILLATOR ELECTRODES 8 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 Department of Biomedical Engineering, SSUET
- 5. 2/14/2014 5 Paddle Electrode Pad Electrode Department of Biomedical Engineering, SSUET 9 DEFIBRILLATOR ELECTRODES DEFIBRILLATOR ELECTRODES Department of Biomedical Engineering, SSUET 10
- 6. 2/14/2014 6 DEFIBRILLATOR ELECTRODES 11 Paddle-type Electrodes have insulated handles Designed to prevent the spread of jell from electrodes to handles for the safety and ease of operator Department of Biomedical Engineering, SSUET Automated External Defibrillator Electrode DEFIBRILLATOR ELECTRODES 12 Department of Biomedical Engineering, SSUET
- 7. 2/14/2014 7 PRINCIPLE OF DEFIBRILLATION 13 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 Department of Biomedical Engineering, SSUET PRINCIPLE OF DEFIBRILLATION 14 Department of Biomedical Engineering, SSUET
- 8. 2/14/2014 8 PRINCIPLE OF DEFIBRILLATION 15 A shorter high-amplitude defibrillation pulse can be obtained by using the capacitive-discharge circuit shown in figure (previous slide) In this case, a half-wave rectifier driven by a step-up transformer is used to charge the capacitor C The voltage to which C is charged is determined by a variable autotransformer in the primary circuit Department of Biomedical Engineering, SSUET PRINCIPLE OF DEFIBRILLATION Department of Biomedical Engineering, SSUET 16 A series resistance R limits the charging current to protect the circuit components, and an ac voltmeter across the primary is calibrated to indicate the energy stored in the capacitor The resistor also helps to determine the time necessary to achieve a full charge on the capacitor The clinician discharges the capacitor when the electrodes are firmly in place on the body by shortly changing the switch S from position 1 to position 2
- 9. 2/14/2014 9 PRINCIPLE OF DEFIBRILLATION 17 The capacitor is discharged through the electrodes and the patient's torso, which represent a primarily resistive load, and the inductor L The inductor tends to lengthen the pulse, producing a wave shape of the type shown in figure (previous slide 14) This situation is determined entirely by the resistance between the electrodes, which can vary from patient to patient Department of Biomedical Engineering, SSUET PRINCIPLE OF DEFIBRILLATION 18 Once the discharge is completed, the switch automatically returns to position 1, and the process can be repeated if necessary With a circuit such as this, 50 to 100 J is required for defibrillation, using electrodes applied directly to the heart When external electrodes are used, energies as high as 400 J may be required Department of Biomedical Engineering, SSUET
- 10. 2/14/2014 10 Classes of discharge waveform There are two general classes of waveforms: a)Mono-phasicwaveform •Energy delivered in one direction through the patient’s heart a)Biphasic waveform •Energy delivered in both direction through the patient’s heart 19 Department of Biomedical Engineering, SSUET Classes of discharge waveform Monophasicpulse or waveform Bi-phasicpulse or waveform 20 Department of Biomedical Engineering, SSUET
- 11. 2/14/2014 11Classes of discharge waveform Fig:-Generation of bi-phasicwaveform 21 Department of Biomedical Engineering, SSUET Classes of discharge waveform The biphasic waveform is preferred over monophasicwaveform to defibrillate A monophasictype, 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 Department of Biomedical Engineering, SSUET
- 12. 2/14/2014 12 About Lab 23 About Lab files Do not copy paste word to word from Internet Do not make a photocopy of your friend’s lab file Marks will be deducted in both above cases Final viva will be conducted based upon whatever you written in your lab file, make sure you know everything Department of Biomedical Engineering, SSUET CARDIOVERTER Department of Biomedical Engineering, SSUET 24 When an operator applies an electric shock of the magnitude of that from a dc defibrillator to the patient's chest during the T wave of the ECG, there is a strong risk of producing ventricular fibrillation in the patient To avoid this problem, special defibrillators are constructed that have synchronizing circuitry so that the output occurs immediately following an R wave, well before the T wave occurs Figure in the next slide is a block diagram of such a defibrillator, which is known as a cardioverter
- 13. 2/14/2014 13 CARDIOVERTER Department of Biomedical Engineering, SSUET 25 CARDIOVERTER Department of Biomedical Engineering, SSUET 26 Basically, the device is a combination of the cardiac monitor and the defibrillator ECG electrodes are placed on the patient in the location that provides the highest R wave with respect to the T wave The signal from these electrodes passes through a switch that is normally closed, connecting the electrodes to an appropriate amplifier The output of the amplifier is displayed on a cardioscopeso that the operator can observe the patient's ECG to see, among other things, whether the cardioversionwas successful-or, in extreme cases, whether it produced more serious arrhythmias
- 14. 2/14/2014 14 AUTOMATIC EXTERNAL DEFIBRILLATOR 27 Department of Biomedical Engineering, SSUET AED AED is a portable electronic device that automatically diagnoses the ventricular fibrillation in a patient Automatic refers to the ability to autonomously analyze the patient's condition 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 28 Department of Biomedical Engineering, SSUET
- 15. 2/14/2014 15 ELECTRODE PLACEMENT OF AED Anterior electrode pad Apex electrode pad Fig. anterior –apex scheme of electrode placement 29 Department of Biomedical Engineering, SSUET 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 shockablerhythm or not 30 Department of Biomedical Engineering, SSUET
- 16. 2/14/2014 16 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 patient 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 31 Department of Biomedical Engineering, SSUET 32 •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 Department of Biomedical Engineering, SSUET
- 17. 2/14/2014 17 IMPLANTABLE DEFIBRILLATORS 33 An implantable cardioverterdefibrillator (ICD) resembles a pacemaker, but its circuitry is similar to that in an AED The battery, capacitor, and electronics are enclosed in a metal case which is implanted under the skin in the chest The typical size of the case, or ‘‘can’’ is about 50x50x15mm Department of Biomedical Engineering, SSUET ICD 34 The capacitors in an ICD are slightly smaller than in an AED, but in an ICD the capacitor is charged to a voltage of only approx. 600 V, implying a charge of 0.075 C and an energy of 23 J An ICD delivers about one tenth the energy that an AED does, but in an ICD the shock is delivered through electrodes placed within the heart and is therefore just as effective for defibrillation Tissue impedance for an ICD is at least 50 ohms, implying a discharge time constant of 5 ms Department of Biomedical Engineering, SSUET
- 18. 2/14/2014 18 ICD 35 Lithium batteries use in ICDs Two batteries in series provide about 6 V Since the capacitor voltage is 600 V, the batteries are used to power a high voltage power supply They are implanted in the patient’s body, so changing them requires surgery, implying that battery lifetime is important the battery performance begins to decay before its total charge is exhausted Also it must provide power for continuous monitoring of the ECG and other functions, so its observed lifetime is 5 years Department of Biomedical Engineering, SSUET ICD 36 Another important property of a battery is the time required to charge the capacitor Typically, the battery takes 10–20 sec to generate a full charge If this time increased significantly, it would delay the delivery of the shock Department of Biomedical Engineering, SSUET
- 19. 2/14/2014 19 ICD 37 The electrodes and their leads are critical components of an ICD Unlike the electrodes in an AED, ICD electrodes are implanted inside a beating heart and must continue to function there for years Many ICD malfunctions arise because of problems with the leads A typical lead contains three electrodes: one for pacing and sensing and two for defibrillation Department of Biomedical Engineering, SSUET ICD 38 The ICD recording lead senses the several-millivoltECG signal within the heart Two parameters that the ICD uses to detect abnormal arrhythmias are heart rate and arrhythmia duration The ICDs use sophisticated algorithms to determine from the ECG if an arrhythmia is present, and these algorithms differ between manufacturers Sufficient memory is included in the ICD to store ECGs before, during, and after a shock Department of Biomedical Engineering, SSUET
- 20. 2/14/2014 20 Reference 39 •For reference visit: •Book: Encyclopaedia of Medical Devices and Instrumentation 2nded. J. Webster (Wiley 2006) •http://www.resuscitationcentral.com/defibrillation/biphasic-waveform/ •http://www.nhlbi.nih.gov/health/health- topics/topics/aed/ •http://www.nhlbi.nih.gov/health/health- topics/topics/icd/ •And various other resources on internet Department of Biomedical Engineering, SSUET