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various type of artifacts in ECG signal & how it's remove


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various type of artifacts in ECG signal & how it's remove

  1. 1. LOVELY PROFESSIONAL UNIVERSITY TERM PAPER On BIOMEDICAL INSTRUMENTATION AND PROCESSINGSubmitted To: Submitted By:Mr. Ansul Mahajan Manish KumarAssist. Prof of LPU Reg.No-10906909 Roll No-B52
  2. 2. ACKNOWLEDGEMENTI’m Manish Kumar, student of B.Tech(ECE) 7th term expressing my deepgratitude to my BIOMEDIC INSTRUMENTATION AND PROCESSINGteacher “Mr. ANSUL MAHAJAN” I am very much thankful to him. I benefiteda lot discussing with him. I am also thankful to my parents who encouraged meand provided such a motivation, so I became able to perform this. I am alsothankful to all my friends and those who helped me directly or indirectly incompletion of my term Paper. MANISH KUMAR
  3. 3. ABSTRACTThe objective of artifacts electrocardiographic (ECG) signals are the observation andassessment of the hearts electrical activity. Electronic advancements have producedinstrumentation with the potential of providing accurate information and reliable heart ratealarms. Computerized monitors enhance patient assessment by allowing uninterruptedelectronic observation of heart rate and ectopic activity with comprehensive automaticreporting mechanisms. Despite these improvements in instrumentation, monitoring systemscontinue to be plagued by problems related to poor signals. Wandering baselines, smallcomplexes, fuzzy tracings, and frequent electrode replacement make patient assessmentdifficult and induce false heart rate alarms. Improvement in electrode preparation techniquesand a better understanding of the sources of artifact can enhance equipment performance,resulting in improved patient assessment, more effective utilization of nursing time, andreduced operating costs. This article discusses the physiologic and non-physiologic sources ofECG monitoring artifact and presents a method of electrode site preparation to reduceartifact.
  5. 5. INTRODUCATIONThe electrical activity of the heart is sensed by monitoring electrodes placed on the skinsurface. The electrical signal is very small (normally 0.0001 to 0.003 volt). These signals arewithin the frequency range of 0.05 to 100 Hertz (Hz.) or cycles per second. Unfortunately,other artifactual signals of similar frequency and often larger amplitude reach the skin surfaceand mix with the ECG signals. In electrocardiography, an ECG artifact is used to indicatesomething that is not heart-made. These include (but are not limited to) electrical interferenceby outside sources, electrical noise from elsewhere in the body, poor contact, and machinemalfunction. Artifacts are extremely common, and knowledge of them is necessary toprevent misinterpretation of a hearts rhythm.SOURCES OF ARTIFACTS IN ECG SIGNALArtifactual signals arise from several internal and external sources.  Internal Arifacts:(1) Signals from muscles and(2) Signals produced in the epidermis  Signals from muscles:All muscle activity produces electrical signals. Signals from muscles other than the heart arecalled EMG signals and appear on the monitor as narrow, rapid spikes associated with musclemovement. These signals are sufficiently dissimilar to the ECG signals that they can beelectronically reduced or "filtered" from the trace. This filtering is readily observed byreduction in the size of EMG signals as the monitor is switched from the diagnostic mode tothe monitor mode. Fig1 shows that when muscle activity produces electrical signal
  6. 6.  Signals produced in the epidermis: The skin is a source of electrical signals which produce motion artifact. Studies have revealed that a voltage of several milli volts can be generated by stretching the epidermis, the outer layer of the skin. This stretching is the primary source of movement-related artifact. This type of artifact is visible as large baseline shifts occurring when the patient changes positions in bed, eats or ambulates. Epidermal artifact is more troublesome than other types of artifact because: (A) it is difficult to filter electronically and (B) ) its amplitude is often larger than the ECG signal. Fig 2. Shows that when skin a sources electrical signal  External Artifacts:(1) 60 Hz. AC interference(2) Offset signals produced by the electrode itself(3) Signals produced by the interaction of body fluids and the electrode gel(4) Lead wire and patient cable problems.(5) Reversed leads.  60 Hz. AC interference:This type of artifact, also called 60 Hz. Interference, produces a wide, fuzzy baseline. It isrelated to poor electrode contact associated with poor skin preparation techniques, driedelectrode gel, or defective patient cables or lead wires.
  7. 7. The source of 60 Hz. pickup is the 60 Hz. current which supplies power to the electrical walloutlets. The 60 Hz. energy "radiates" from the electrical wiring in the patients room and isreceived in the lead wires and by the patient. The source of radiation cannot be eliminated,but modern monitors can reduce 60 Hz. pickup by filtering and by an electronic techniquecalled common mode rejection. This technique requires good skin contact by all electrodes.One or more electrodes with poor contact will result in the wide fuzzy baseline.Alternating current (AC) describes the type of electricity that we get from the wall. In theUnited States, the 60 hertz. Many places in Europe use 50 Hz AC electricity. When an ECGmachine is poorly grounded or not equipped to filter out this interference, you can get a thicklooking ECG line.fig 1. Fig 3 shows that when AC power to the electrical wall outlets.  2) Offset signals produced by the electrode itself:An offset potential is a voltage that is stored by the electrode. This stored voltage will add tothe ECG signal and interfere with it. The offset potential causes the disappearance of theECG after defibrillation. The amount of offset potential and the length of time required for itto dissipate are determined by the materials used for the electrode and the gel. Certaincombinations of metals and gels generate large voltages (up to 200 millivolts) with the abilityto hold this voltage for long periods of time. Electrode materials such as silver-silver chloridedo not allow significant build-up of offset potential, whereas stainless steel electrodes havepoor offset characteristics. Most electrodes used for ECG monitoring today are made ofsilver-silver chloride. With the common use of the silver-silver chloride electrode, offsetpotentials are no longer considered to be a significant problem. Fig 4. Shows that when offset potential voltage that is stored by the electrode
  8. 8.  Signals produced by the interaction of body fluids and electrode gel:Movement of the electrode gel under the electrode was thought to be the primary cause ofmotion artifact. The electrode gel does, however, significantly affect the transmission ofsignals from the skin to the electrode. The lack of sufficient electrode gel, frequently due toevaporation caused by improper storage, results in 60 Hz. pickup and extremely unstabletraces. This type of artifact is easily identified by very high electrode impedancesElectrode impedancesIn order for ECG signals to pass from the body to the electrode, an electrically conductivepath between the skin and electrode must be established. The conductive ability of this path isreferred to as electrode impedance or contact impedance. Electrode impedance is measured inohms. High impedance decreases the conduction of the ECG signal. Low impedancesimprove this conduction. The major factors affecting electrode impedance are:(a) The quantity and quality of gel between the electrode and the patient and(b) The degree to which the outer layer of the epidermis has been bridged by the conductivegel.Proper site preparation will produce contact impedances of 10,000 ohms or less in 90% ofpatients.9 Less than 5,000 ohms is a good target value. Improper site preparation will usuallyproduce contact impedances as high as 1M to 2M ohms. Fig 5. Shows that when movement of electrode.  Lead wire and patient cable problems:Breaks in the wires and connections between the electrode and the monitor will always be asource of monitoring problems. Poor contact at any snap connection, loose pins at the cableend of the lead wire, and breaks in the conductors of the lead wire or patient cable can causeintermittent loss of the ECG tracing, 60 Hz. Pickup.
  9. 9.  Reversed leads:Electrode/lead placement is very important. If one were to accidentally confuse the red andwhite lead cables i.e. place the white one where the red one should go, vice versa, he mightget an ECG that looks like figure 6. In this ECG, we can make out a normal sinus rhythmwith all of the waves upside-down. When this happens, you are essentially viewing therhythm in a completely different lead. One must also make sure that the lead wires areactually plugged into the machine. If your talkative patient shows a systole, you shouldsuspect this. Many machines are smart in that they can sense common errors of this nature,but many such errors arent always readily apparent.Fig 6. Shows that when elerode are wrong placed.ARTIFACTS REMOVAL IN ECG SIGNALSThe electrical activity of the heart is sensed by electrodes that are placed on the skin’ssurface. The heart’s electrical signal is very small (normally 0.0001 to 0.003 volt), andunfortunately this can be combined with artifactual signals of similar frequency and oftenlarger amplitude.Each patient’s ECG is unique. The patient’s size, skin type, age, and pathology, as well aswhere the electrodes are placed, influences the results of the tracing. Poor signal quality cancause noise or artifacts on the ECG, which in turn leads to inaccurate analysis of the ECG.Now different Method to minimize the artifacts in ECG signal  Perform good skin preparationThe build-up of skin oils and residues increases the resistance to the conduction of theelectrical signal.  Check for AC interference
  10. 10. 50/60 Hz. interference looks like small regular peaks and produces a wide, fuzzy baseline. Itis traced to the 50/60 Hz. current which supplies power to the electrical wall outlets. The50/60 Hz. energy radiates from the electrical wiring inthe patient’s room and can be picked up by the patient and/or the lead wires. This will resultin AC interference on the ECG tracing. There are several causes of AC interference:• Electrical wires in the walls, ceiling or floor.Suggestion: Move the examination table away from walls  Check the electrodesCheck the electrode gel to make sure it is fresh and moist. The electrode gel greatly affectsthe transmission of signals from the skin to the electrode. A dry electrode with inadequateconducting gel will not work properly since it reduces the conduction of the ECG signal. Inmost instances, electrode gel dry-out is simply a result of incorrect storage. Electrodes arepackaged in metal foil pouches to prevent gel evaporation. Use this point• Use electrodes prior to their expiration date.• Do not remove the electrodes from their pouch until they are ready to be used.  Verify filter settings in the deviceFinally, if the tracings are still showing artifact, make sure that the following filters are turnedon:• Muscle filter• AC filter• Wandering baseline filter  Make sure the patient is warm, relaxed and does not move or speakIt is important to make sure the patient is warm and relaxed during the test because we wantto reduce muscle tremors and movement as much as possible since they can impair thequality of recordings.Filtering methods • High pass filtering (HPF) • Adaptive filtering (AF) • Kalman filtering(KF)
  11. 11. In signal processing, there are many instances in which an input signal to asystem contains extra unnecessary content or additional noise which candegrade the quality of the desired portion. In such cases we may remove orfilter out the useless samples.CONCLUSIONArtifact in ECG monitoring can be annoying, costly, and dangerous. An understanding of thesources of artifact and care in the application of monitoring electrodes can significantlyreduce or even eliminate the problem. The filter robustness is crucial for ECG artifactremoval. Artifacts removal method now days very easy to design because there are no. Offilter devices available in market so we reduce easily to remove artifacts.REFRENCES: o BIOMEDICAL SIGNAL ANALYSIS: A CASE-STUDY APPROACH, Author RANGARAJ M. RANGAYYAN , Edition 1st, Publisher Name-Wiley, Year-2009,chap-3. o Tam, H.W. and Webster, J.G. Minimizing Electrode Motion Artifact by Skin Abrasion. Institute of Electronic and Electrical Engineers (IEEE) Transactions on Biomedical Engineering (BME), 24(2): 134-139, 1977 o Knight, BP; Pelosi, F; Michaud, GF; Strickberger, SA; Morady, F; Clinical consequences of electrocardiographic artifact mimicking ventricular tachycardia. N Engl J Med 1999; 341:1270–1274.