Solutions

Case3 Various Artifacts

Electrodes are attached correctly but the waveform shown on the display is not clear enough. It seems it has some kind of artifact.

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Some models are designed to alert the presence of artifacts and all of Nihon Kohden's ECG systems are equipped with various anti-artifacts filters and other means to minimize them. However, artifacts can still occur and prevent the acquisition of a clear ECG waveform. In this case, it is required to identify the type of artifacts and take specific actions depending on where they come from. The causes of artifacts can generally be divided as follows;

Artifacts from the ECG system itself: Breaking of lead and/or power cables, dirt and rust on electrodes, bad contact at connectors, etc.
External artifacts: AC artifacts, EMG (electromyogram), base line drift, static electricity, electromagnetic interference, etc.

 

Artifacts from the ECG System Itself

Feature: Irregular noise occurring occasionally or continuously.
Countermeasures: If the artifacts changes when a lead cable is shaken, bent, or unplugged and plugged, firmly reinsert the connector. If this does not help, replace the lead cable. The artifacts caused by dirt or membrane on the electrode can be solved by cleaning. Check electrodes and cable tips to ensure that there is no dirt.

Artifacts from cable disconnection

External Artifacts

The artifacts coming from outside the ECG system can be divided generally into (1) AC artifacts, (2) EMG, (3) drift, and (4) static electricity.

(1) AC Artifacts

Features: Presence of relatively constant 50-Hz or 60-Hz sinusoidal waves.

ecase3-2.png

Countermeasures: AC artifact can result from causes a) ~ c) below, each of which would require different countermeasures.

a) Artifact from Electrostatic Induction
AC power cables used on walls and ceilings, combined with the patient’s body, can create a situation where a capacitor is formed and an AC current flows between them, resulting in disturbance of the ECG. In this case, observe the situation carefully and try the followings;

  • Move the patient away from electric cables
  • Unplug all power cables from electrical appliances that are not necessary
  • Try moving the bed to a different position
  • Cover with a shield sheet

Ways to avoid electrostatic induction

b) Artifacts from Electromagnetic Induction
An electric current in a power cable produces magnetic lines of force around it. When they cross a lead wire or a human body, an electromotive force is generated there. Artifacts from electromagnetic induction are difficult to eliminate, and covering with a shield sheet is often ineffective. Try the followings; 

  • Avoid the use of electrical appliances as much as possible around the patient
  • Try moving to a different place
  • Bundle lead cables as much as possible (this makes them less sensitive to electromagnetic induction)

Ways to avoid electromagnetic induction

c) Artifacts from Leakage Current
This type can be caused either by the leakage current from the power cable of the ECG system via the lead wires to the patient, the bed, and the floor or by the leakage current occurring in the floor or wall flowing into the patient, disturbing ECG recordings. Try to; 

  • Securely connect the ground wire to the ECG system
  • Place a shield sheet between the patient and the bed and ground the shield sheet
  • Electrically insulate the bed by using rubber dishes under bed legs

To avoid leakage current

(2) EMG Artifacts

Features: Continouous presence of irregular jagged noise.

Irregular jagged noise

Countermeasures: EMG artifacts can occur when the patient’s body is stiffened due to nervousness, when the patient’s hand or foot is slid down from the bed, when the limbs are constricted by clothes, or when the room temperature is too low. Try to;

  • Explain the details of the test so that the patient can feel more relaxed
  • Prepare the bigger bed to provide more space
  • Check that clothes are sufficiently loose
  • Keep the room warm
  • Ask the patient to go to the bathroom beforehand

(3) Base Line Drift

Features: The base line changes slowly. It moves with breathing.

base line drift caused by breathing

 

base line drift caused by electrode movement

Countermeasures: One of the causes is the change in polarization potential that develops between the electrode and the paste. Drift occurs when the electrode is moved as a result of the motion of the patient. Drift also occurs when the electrode is touching any clothing and when breathing heavily. Take the following measures;

  • Prevent electrodes from touching any clothing
  • Ask the patient to breathe gently
  • Wipe sweat, if any, with a cold towel
  • Keep the room warm
  • Ask the patient to go to the bathroom beforehand

(4) Static Electricity

Features: Spike-like artifacts.
Countermeasures: Static electricity may cause artifacts in the ECG when the air is dry, such as in winter. A strong electrical discharge or spark may damage the ECG system. Take the following measures;

  • Humidify the room, e.g., using a humidifier
  • Replace partition curtains and patient’s gowns with materials that are less likely to hold static charges if they are made of synthetic fabrics
  • Replace slippers with conductive slippers if they are worn on a carpeted floor