How to apply electrodes for ECG

Author Ольга Кияница


Electrocardiography is the main method for studying the electrical activity of the heart. Many heart diseases are determined precisely by an ECG, which is additionally a relatively affordable way to diagnose. To obtain accurate results, electrodes must be properly applied during ECG recording.

Standard 12-vector electrocardiography (ECG) is an important diagnostic method that allows you to register the electrical activity of the heart. An ECG is necessary to determine the appropriate treatment for patients with various cardiovascular diseases, which are often life-threatening and require immediate medical attention.

Modern ECG devices are portable, inexpensive, and easy to use, and these features make it easy to record in a variety of patient locations, including hospitals, operating rooms, ambulances, sports facilities, and social facilities.

The task of an ECG is to provide high-quality, consistent recording methods regardless of the clinical course of the disease. An ECG recording that is not performed in accordance with accepted standards can lead to incorrect diagnoses and treatment.

Video: 12 Lead ECG Explained, Animation

Preparing the patient for an ECG

Although the 12-vector ECG is performed in different situations, places, and time gaps, attempts to achieve the best results are associated with the standards for applying electrodes, which must always be strictly followed.

  • The position of the patient

Many patients feel uncomfortable on a strictly horizontal surface, therefore, to ensure correct results, a reclining position of approximately 45 degrees is recommended. Any significant deviations from this indicator should be noted in the ECG description.

Various studies have shown that a recorded ECG in a patient in a supine position may differ significantly from the results of a study of the same person, only standing upright or inclined at an angle of 60 degrees or more. At the same time, there is no evidence that a change in the patient's inclination between the horizontal and 45 degrees relative to the horizontal plane has a significant effect on the ECG recording.

Limbs should be located on a bed or couch to minimize the appearance of artifacts due to muscular tension.

It is necessary that the patient was in a relaxed and comfortable state for himself. If these conditions are not met, an ECG can register somatic muscular potentials as well as obstructed heart activity.

Some patients cannot fully relax due to painful conditions, such as arthritis, or they have Parkinson's disease, which causes tremor. These patients should be located as conveniently as possible, and the resulting ECG should be accompanied by an appropriate explanation, especially if it is not very high quality.

Before recording the ECG, the patient’s limbs are checked, which should remain in a relaxed state. If the patient clenches his fists, strains his hands or moves his fingers, it is impossible to obtain a high-quality ECG.

  • Skin preparation

To register an ECG without artifacts, preliminary skin preparation is often required. This is especially true for patients with sensitive or damaged skin. There are various ways to minimize skin impedance (resistance) to the electrode, for example:

  • The skin must be cleansed beforehand. There are many methods, including washing the skin with mild soap.
  • Exfoliation may be required, which should be done with very light movements using a paper towel, gauze pad or proprietary abrasive tape designed for this purpose.
  • Sometimes it is necessary to remove the hair from the chest in order to ensure proper contact of the electrodes with the skin. For this, the patient must give oral consent.

Electrode Characteristics

Electrodes are arranged in accordance with modern recommendations. If any of the electrodes must be in an irregular position,
this should be noted in the ECG record in order to avoid further misinterpretation of the changes on the ECG.

Lead wires to the electrodes are usually color-coded for proper identification. However, color may vary by manufacturer.Color affiliation, as a rule, is described in detail in the accompanying document, which, in turn, complies with European recommendations.

Note on the use of electrodes: disposable electrodes should be in good condition and not be outside the package, which contains the date of use.

The electrodes are in good condition if the “core” of the electrode has not dried. In this case, the electrodes should be stored inside the foil package to prevent dehydration of the gel.

Arrangement of electrodes

Electrode pads should be located on the proximal (remote) parts of the limbs, that is, on the wrists and ankles. Moving the electrodes up the limbs can change the appearance of the ECG. For this reason, such a movement should be avoided if there is no significant tremor or amputation of the limb.

Note: electrode pads should not be placed on the torso, as this causes a significant change in wave amplitude.

Positioning electrodes on the limbs:

  • Right hand (RA, red) - superimposed on the right forearm, closer to the wrist.
  • Left hand (LA, yellow) - superimposed on the left forearm, closer to the wrist.
  • Left leg (LL, green) - superimposed on the left leg, closer to the ankle.
  • Right leg (RL, black) - superimposed on the right leg, proximal to the ankle.

Positioning the electrode on the chest

There is a definition of proper anatomical overlapping of the electrodes on the chest. Similar installations should always be used. If for some reason the standard overlap of the electrodes is not possible, then the center of the active region of the sensors must be aligned accordingly with the anatomical landmarks.

Studies have shown that V1 and V2 electrodes are often placed too high, and V4, V5, and V6 electrodes too low. These errors can lead to diagnostic errors due to a change in the ECG waveform.

The location of the electrodes on the chest (chest):

  • V1, red (C1) - the fourth intercostal space on the right side of the sternum.
  • V2, yellow (C2) - the fourth intercostal space on the left side of the sternum.
  • V3, green (C3) - in the middle between V2 and V4.
  • V4, brown (C4) - the fifth intercostal space in the midline of the clavicle.
  • V5, black (C5) - left anterior axillary line at the same horizontal level as V4.
  • V6, purple (C6) - left mid-axillary line on the same horizontal level as V4 and V5.

Method of determining the location of the electrodes on the chest

The exact identification of the relevant intercostal spaces should begin with the definition of the sternum angle, also known as the Louis angle.

  • To determine the angle of Louis, the fingers must be lowered down the sternum from top to bottom until a bone horizontal formation is achieved. Next, the fingers move downwards and the second intercostal space will be determined on the right side. From here it is possible to count to the third and fourth intercostal spaces. In the fourth intercostal space near the edge of the sternum is the location of the electrode V1.
  • The above method of determination should be repeated on the left side to allow the electrode to be correctly positioned at point V2. It should be noted that the left and right intercostal spaces can be displaced, so you should avoid placing V2 near V1, not counting intercostal spaces.
  • The electrode at point V4 should be placed in the fifth intercostal space along the line running in the middle of the clavicle.
  • The electrode at point V3 should be placed in the middle of the gap between points V2 and V4.
  • Electrodes at points V5 and V6 should be placed along a horizontal line passing through point V4. The V5 electrode should be placed on the anterior axillary line; The V6 electrode is located along the mid-axillary line.

Features overlapping electrodes

  • In order to achieve an accurate and correct positioning of the electrode during ECG registration, it is usually necessary for all subjects to release the upper body from clothes.
  • When registering an ECG in women, it is customary to place electrodes at V4, V5 and V6 points under the left breast, which normally covers the correct anatomical points of electrodes superposition.
  • There is some evidence that positioning electrodes at points V4, V5 and V6 above the chest cannot significantly weaken the signal. In some cases, additional supporting evidence is needed to ensure that this recommendation is modified.
  • When lifting the breast for applying electrodes require special handling and delicacy, so it is best when the patient herself will support the breast.

Note. If overlapping electrodes varies from recommended installation points, it is important that this is documented in the ECG description, including the ECG in the electronic storage version.

Getting a good quality record

A 12-vector standard ECG is most often recorded on a tape at a speed of 25 mm / s with a gain setting of 10 mm / mV.To start recording, the corresponding button must be pressed; which is usually referred to as “start” or “auto”.

All filters must be turned off during the initial attempt at ECG recording. A low-speed filter reduces interference, but also distorts the ECG, so that it can only be used if necessary, and only after unsuccessfully eliminating interference with other filters.

If, despite efforts to relax the patient and create a comfortable environment, muscle contractions interfere with the ECG, the filter can be turned on and the recording is repeated. Use of the filter should be clearly identified in the ECG inventory.

Any ECG functions that may indicate the need for an urgent medical examination should be brought to the attention of medical personnel. If the patient has any symptoms of possible cardiac origin during the recording, such as chest pain, palpitations or dizziness, this should also be noted in the ECG description.

Confirmation that the ECG was recorded in good quality, is the conclusion of a doctor. Record evaluation is performed to ensure that all waveforms (such as P-waves, QRS complexes and T-waves) are clearly visible. The isoelectric line (baseline between ECG deflections) must be stable, non-wandering, and free from interference.

At the end of the procedure, all electrodes must be removed from the patient, and disposable electrodes disposed of as medical waste.

Video: How to perform a 12 lead ECG

Source 1.  Электрокардиография - Ярцев С.С. 2014. 2.  Руководство по клинической ЭКГ - Де Луна А.Б. 1993. 3.  Электрокардиография - Мурашко В.В., Струтынский А.В. 4.  Electrocardiography - R. Joe Noble, J Stanley Hillis, and Donald A. Rothbaum.

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