The 12 lead Electrocardiograph (ECG) is the most common cardiac investigation carried out.
It provides the clinician with a wealth of important data, which includes measurement and interpretation of heart rate and rhythm; information about the chambers of the heart and potential effects of certain medication and electrolyte imbalance on the electrical activity of the heart. It is also key in the diagnosis of cardiac ischaemia and infarction and can also be useful in picking up inherited cardiac conditions. However inaccurate recording of the ECG can potentially result in an incorrect diagnosis which in turn may lead to either incorrect treatment or lack of appropriate treatment. Therefore, it is crucial that it is recorded accurately.
To help ensure this is the case, here are some tips to get it right.
Understand the terminology.
One of the most confusing things for practitioners when they first learn to record a 12 lead ECG is that there are only 10 leads that are attached to the patient. The 12 leads refer to the 12 views of the heart that the ECG records. If we think of the wires as electrodes this can minimise confusion.
Other terminology that is used refers to the 12 leads that are recorded. 6 of the leads are the limb leads and are made up from the electrodes that have been attached to the arms and legs. The other six are known as the chest leads or precordial leads. These will either have v1 – v6 on the electrodes or c1- c6 depending on the machine used.
Know the machine.
While all ECG machines should give 12 leads on the printout, they may work slightly differently. Some things to check are:
• Does the machine need to be plugged in or can it work on battery?
• How do you insert new paper if it runs out?
• Are there enough sticky dots (to attach the electrodes to)?
• Can you enter patient details?
• Is there equipment such as a razor and alcohol wipes if required with the machine?
• Prior to recording the ECG, calibration needs to be set at 25mm/second (paper speed) and the voltage at 10mm/mv. If these have been altered it will affect the interpretation of the ECG.
• Does the ECG show up on a screen prior to being printed? This allows the user to check that there are no issues such as artefact or an electrode that has come off.
• How does it appear on the paper? Many machines will have all 12 leads printed (6 limb leads on the left side and 6 chest leads on the right) with the rhythm strip printed underneath, however other machines will use a different printed format.
Prepare the Patient.
For clinicians an ECG can seem like a very simple, routine investigation. However, the patient may not see it in the same light. If they are anxious this can lead to muscle contraction which can lead to artefact. Often an ECG may be recorded while someone is experiencing chest pain. It is important to try and relax the patient and make them as comfortable as possible. Privacy and dignity are really important. If possible provide a gown for them to put on after the electrodes have been attached. Don’t forget to ask if they want a chaperone.
In order for the sticky dots to attach properly any excess hair may need to be shaved. The skin needs to be dry and free from oil or sweat. If necessary gauze can be used to remove loose, dry skin.
Explain the procedure to them and any potential follow up or treatment that may result.
Know Where to Place the Electrodes.
One of the biggest reasons for inaccurate recordings is the technique of ‘eyeballing’ where the clinician places the electrodes in the locations that they believe are correct. This is particularly the case for leads V1, V2 and V4.
As the wires connecting the limb electrodes are longest I would recommend doing these first as they are less likely to fall off. The electrodes should be placed on the wrists and the ankles. Although it is common practice to place these on other parts of the limb this again can lead to inaccuracy in interpretation. If there is a reason that this needs to be done e.g. amputee this should be noted on the ECG.
The red electrode is connected to the right wrist, yellow to the left wrist, green to the left ankle and black to the right ankle. Some people like to remember it by the pneumonic RYGB – ride your green bike.
The correct location for the chest leads are as follows:
V1 – 4th intercostal space at the right sternal border (edge)
V2 – 4th intercostal space at the left sternal border (edge)
V3 – midway between V2 & V4 (do this after you have placed V4)
V4 – 5th intercostal space, midclavicular line (in women place under breast tissue)
V5 – left anterior axillary line (in line with the armpit crease), same horizontal plane as V4
V6 – Left midaxillary line (in line with the centre of the armpit), same horizontal plane as V4 & V5
Points to remember to help get this right:
• The distance between V1 and V2 shouldn’t be more than 3.5cm.
• Intercostal spaces are below the ribs and not above (the first space below the clavicle is the infraclavicular space)
• The nipple shouldn’t be a guide for where to put V4
Once the procedure is complete, check the printout to ensure that all 12 leads are represented. If the printout is not clear or there are leads missing, then repeat the process.
Ensure that the patient’s name, date time and any symptoms they were experiencing at the time are recorded on the ECG.
Remove the electrodes and make the patient comfortable. If the ECG needs to be repeated within a short period of time, it may be advisable to leave the sticky dots in place if possible.
Written by Kate Olson, 13th February 2018