Case1 To Record Clear Standard 12-Lead ECG and Electrode Positioning

What is ECG? Where and how do we attach probes to patients to record clear ECG?

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An ECG is one of the basic physiological tests widely used in clinical examination. It is performed as an essential part of a first assessment, particularly in a case where a cardiovascular disease is suspected. Because ECG diagnosis provides an important basis for subsequent treatment, it is crucial that we acquire ECG recordings containing as little artifacts as possible.
Necessary steps to achieve this goal is to check the waveforms before we start recording and then eliminate the cause of the artifacts, if there is any.

an image of a patient lying on a bed with electrodes attached

Electrode Positioning

Attaching electrodes in the correct positions is the first step to producing an ECG recording that can be useful for diagnosis. A standard 12-Lead ECG is useless if the electrodes are not attached correctly. The positions of the electrodes and the colors of the lead wires are shown below. There are IEC and AHA ways to attach electrodes;

illustration of electrode positioning for limbs and chest


Positioning of electrodes -IEC-

Check 1: Attach chest electrodes in the correct position

The correct electrode locations are particularly important for chest leads. Even if they are misplaced by the width of one intercostal space, it may significantly alter the recorded waveform.

example of waveform, resulting from attaching chest electrodes to the wrong site

Check 2: Positions of limb electrodes can be changed

It is believed that the positions of limb electrodes can be changed without causing significant alteration in the waveform as long as they are located in between the wrist and the base of the arm, and in between the ankle and the groin. If it is difficult to attach an electrode on the wrist or the ankle, try using different positions.

example of waveforms, resulting from attaching limb electrodes to the wrong site

How to Attach Electrodes

  1. Connect each electrode lead wire to the corresponding electrode by inserting the connector tip fully into the electrode base. When connecting limb electrodes, match the colors of the lead tips with the colors of the clips. If the connection between the tip and the electrode is loose, tighten it by crimping the connector part of the electrode.
    a picture of fully inserted electrode a picture of tighten the connecting part or electrode
  2. Wipe the skin at the electrode attachment sites with alcohol to remove sebum.
  3. Rub the paste (cardio Cream) sufficiently onto the electrode attachment sites. When working on chest electrode attachment sites, make sure that adjacent sites do not have paste in contact with each other.

    a bad example of putting paste paste

  4. Apply cardio Cream thinly onto the contact surfaces of the electrodes.
  5. Attach chest electrodes to the attachment sites by pinching the rubber suction bulbs. Make sure that the electrodes do not touch each other.

    a bad example of electrodes attached right next to each other

  6. Attach limb electrodes to arms and legs on soft skin. Use a clip-type electrode (Fast Clip) on the attachment site so that the electrode adheres to the skin.


  • All limb and chest electrodes should be of the same type and manufactured at the same time. Mixed use of electrodes made of different materials (e.g., suction electrodes and disposable electrodes) or those manufactured at different lot number may increase the polarization potential, resulting in more artifacts (hum and/or drift). It may even not be possible to acquire an ECG waveform at all.
  • After use, clean the electrodes to remove the remaining paste by wiping or rinsing off using water and dry them well. If not cleaned after use, electrodes may rust and become more sensitive to artifact.
  • When using new electrodes, it is recommended to use after aging treatment, such as soaking in physiological saline overnight, for better stability.

Checking the Condition of Electrode Attachment

If the ECG system has the specification to check the condition of electrode attachment, there will be a notification of any detached electrodes or the presence of artifacts on the display screen. Read the message and take necessary actions.

a message about detached electrodes will be shown on the display