For researchers, it is vital to capture clear ECG signals in order to gain accurate insights and results.
But it can be a real challenge to record clean signals, especially when performing a 12-lead ECG. There are numerous elements to get right: the data recording equipment needs to be set up correctly, the subject needs to be comfortable, and you need to position the surface electrodes on the subject's torso and limbs precisely in order to get results that you can interpret accurately.
Here is our simple guide for correctly placing surface electrodes when performing a 12-lead ECG:
What is an ECG?
Electrocardiography studies the heart's electrical activity produced during myocardial contraction and relaxation, usually recorded by electrodes on the skin. The resulting graph of voltage versus time is called an electrocardiogram - often abbreviated as ECG (or EKG). For research, ECG signals are recorded to examine heart rate, heart rate variability, analysis of the waveform morphology, arrhythmia and other similar functions.
Why is correct electrode placement for a 12-lead ECG so important?
ECG electrode placement is standardized, allowing for the recording of an accurate trace – and it also ensures comparability between records taken at different times.
Poor electrode placement can result in mistaken interpretation and inaccurate results. Deviation of lead placement even by 20-25mm from the correct position can create clinically significant changes on the ECG, including changes to the ST-segment (McCann et al. 2007).
Subject factors may also contribute to the variability in accuracy, including the subject’s respiration, position, smoking, recent dietary intake, and obesity (McCann et al. 2007).
It is, therefore, important to not only ensure that the electrodes are placed in accordance with the standardized ‘rules’ but also, that the subject is prepared correctly, both physically and psychologically for the procedure.
Preparing a Subject for an ECG
Preparing the subject's skin properly is vital. Ensure their skin is clean and dry. Use an alcohol wipe to swab the areas where you will be placing the electrodes to remove any residues of creams or lotions.
Subjects with chest hair should have the hair at the electrode placement sites removed with a razor (Coviello 2016).
If it is possible, ask your subject to sit in a semi-recumbent sitting position, where their torso and head are reclining at about a 45-degree angle (Baillie 2014). If this is not possible or uncomfortable, the ECG can still be carried out in a different position, as long as the subject is comfortable.
The subject needs to be relaxed. Make sure the environment is at a comfortable temperature (Jevon 2010). This stops muscular tension or movements that might produce artifact on your ECG recording. Also, ensure privacy and dignity by closing the room door or drawing the curtains.
12-Lead ECG Placement
The subject's chest and all four limbs should be exposed in order to apply the ECG electrodes correctly.
There are different methods for identifying the correct landmarks for ECG electrode placement, the two most common being the ‘Angle of Louis’ Method and the ‘Clavicular’ Method (Crawford & Doherty 2010a).
Regardless of the method used, the ECG electrode positions should be found in the following locations:
|V1 (C1)||Fourth intercostal space at the right sternal border|
|V2 (C2)||Fourth intercostal space at the left sternal border|
|V3 (C3)||Halfway between leads V2 and V4|
|V4 (C4)||Fifth intercostal space in the midclavicular line|
|V5 (C5)||Left anterior axillary line on the same horizontal plane as V4|
|V6 (C6)||Left midaxillary line on the same horizontal plane as V4 and V5|
|RA (R)||Right arm (inner wrist)|
|LA (L)||Left arm (inner wrist)|
|RL (N)||Right leg (inner ankle)|
|LL (F)||Left leg (inner ankle)|
|Unbracketed letters indicate lead names under the American Heart Association (AHA) system; bracketed letters indicate lead numbers under the International Electrotechnical Commission (IEC)|
(Table adapted from Crawford and Doherty 2010a; Jevon 2010; Cable and Sensors BV n.d.)
Precordial Lead Placement
In order to find these correctly, the ‘Angle of Louis’ Method can be used, as outlined in the video above:
- To locate the space for V1; locate the sternal notch (Angle of Louis) at the second rib and feel down the sternal border until the fourth intercostal space is found. V1 is placed to the right of the sternal border, and V2 is placed at the left of the sternal border.
- Next, V4 should be placed before V3. V4 should be placed in the fifth intercostal space in the midclavicular line (as if drawing a line downwards from the centre of the subject's clavicle).
- V3 is placed directly between V2 and V4.
- V5 is placed directly between V4 and V6.
- V6 is placed over the fifth intercostal space at the mid-axillary line (as if drawing a line down from the armpit).
- V4-V6 should line up horizontally along the fifth intercostal space.
The Clavicular Method is useful as a check, but Crawford and Doherty (2010b) advise that inexperienced practitioners may mistake the sub-clavicular space as the 1st intercostal space; meaning that the intercostal spaces are incorrectly identified.
Limb Lead Placement Diagram
Breast tissue can impact the ECG amplitude due to the increased distance between the electrode and the heart when ECG electrodes are placed over the chest (Rautaharuju et al. 1998).
The V4 lead is recommended to be placed underneath the breast tissue in women. Crawford and Doherty (2010b) point out that it makes little sense to locate the correct position under the breast, to then replace the breast and attempt to approximate the correct location. Thus, they recommend that V4 should be placed under the breast, and V5 and V6 placed underneath too if lifting the breast is needed.
It is often customary in practice to write on the ECG if an electrode has been placed over breast tissue in order to aid the interpretation.
Where it becomes necessary, it is also customary practice to record any alterations in lead placement; for example, where lead placement is changed from the standardized location due to subject position, injury etc.
End of Procedure
Ensure that the subject's privacy and dignity are maintained. The chest should not be left exposed and can be covered back up with blankets, or allow the subject to re-dress as necessary.
The ECG electrodes should be removed if the subject is not likely to require further or serial ECGs, but otherwise can be left in place for up to 24 hours before needing to be replaced (Coviello 2016).
- Baille, L 2014, Developing practical nursing skills, 4th edn, CRC Press, Florida.
- Coviello, J 2016, ECG Interpretation made incredibly easy, 6th edn, Wolters Kluwer, London.
- Crawford, J & Doherty, L 2010a, ‘Ten steps to recording a standard 12-lead ECG’, Practice Nursing, vol. 21, no. 12, pp. 622-29, viewed 13 March 2018, https://www.magonlinelibrary.com/doi/abs/10.12968/pnur.2010.21.12.622.
- Crawford, J & Doherty, L 2010b, ‘Recording a standard 12-lead ECG: Filling in gaps in knowledge’, Journal of Paramedic Practice, vol. 2, no. 3, pp. 102-8, viewed 13 March 2018, https://www.magonlinelibrary.com/doi/10.12968/jpar.2010.2.3.47285
- Jevon, P 2010, ‘Procedure for recording a standard 12-Lead electrocardiogram’, British Journal of Nursing, vol. 19, no. 10, pp. 649-51, viewed 13 March 2018, https://www.ncbi.nlm.nih.gov/pubmed/20622761
- Khunti, K 2013, ‘Accurate interpretation of the 12-lead ECG electrode placement: A systemic review’, Health Education Journal, vol. 73, no. 5, pp. 610-23.
- McCann, K, Holdgate, A, Mahammad, R & Waddington, A 2007, ‘Accuracy of ECG electrode placement by emergency department clinicians’, Emergency Medicine Australasia, vol. 19, pp. 442-8, viewed 13 March 2018, https://www.ncbi.nlm.nih.gov/pubmed/17919217
- Medani, S, Hensey, M, Caples, N & Owens, P, 2018, ‘Accuracy in precordial ECG lead placement: improving performance through a peer-led education intervention’, Journal of Electrocardiology, vol. 51, pp. 50-4, viewed 13 March 2018, https://www.ncbi.nlm.nih.gov/pubmed/28576322
- Rautaharju, P, Park, L, Rautaharju, F & Crow, R 1998, ‘A standardized procedure for location and documenting ECG chest electrode positions: Consideration of the effect of breast tissue on ECG amplitudes in women’, Journal of Electrocardiology, vol. 31, no. 1, pp. 17-29, viewed 13 March 2018, https://www.ncbi.nlm.nih.gov/pubmed/9533374.