Electrocardiogram (ECG) recording

An electrocardiogram (ECG) is a recording of the electrical activity within the heart muscle. It is the most commonly performed cardiac test.

Article by Charles Bloe

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The operator should be competent in both the use of the electrocardiograph (the ECG machine) and in the recording of an electrocardiogram (the ECG trace). Operators should provide evidence of having undertaken a practical assessment process that has been carried out by another competent and suitably qualified practitioner. Local guidelines should be adhered to.

The human heart

The human heart is a hollow, conical organ that is located in the thoracic cavity behind the sternum, lying about one-third to the right and two-thirds to the left of the mediastinum. It weighs approximately 300 grams and is about the size of a clenched fist.

There are four heart chambers, the two upper atria and the two lower ventricles. The smaller atria are the filling chambers and the larger ventricles are the pumping chambers.

The average human heart beats 100 000 times each day, pumping over 7500 litres of blood

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The 12-lead ECG is the most commonly performed diagnostic procedure in cardiology (Kligfield et al, 2007). It may be recorded to give baseline information or investigate specific concerns or symptoms. 

A 12-lead ECG may be indicated in the following situations:

  • chest pain - the main presenting symptom in acute cardiac disease
  • acute coronary syndrome
  • investigating symptoms, such as palpitations, syncope, bradycardia, tachycardia, hypertension, hypotension, breathlessness
  • monitoring the effect of medications
  • following successful cardiopulmonary resuscitation (CPR)
  • cardiac arrhythmias (eg used to investigate the cause of an irregular pulse)
  • pre-operative assessment
  • routine medical admission or assessment

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Before recording a 12-lead ECG, the necessary equipment should be gathered.


Large choices of electrocardiographs are available. Operators should familiarise themselves with the machine to be used. Although personal experience, preferences and resources will dictate which machines are purchased, it is important that electrocardiographs meet or exceed the requirements of IEC 60601-2-51 (2003). The device should be pre-programmed in accordance with American Heart Association specifications. The operator should ensure that the date and time settings are correct. The patients’ details, such as name and date of birth, should be confirmed and entered into the ECG machine. Some interpretative machines request further detail, such as clinical history and medications, and where time permits these details should also be entered.

Monitoring cables

Each ECG lead cable is colour-coded to aid identification. Check that the cables are not broken or twisted as this may result in interference (Metcalfe, 2000).


Disposable tab

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Patient preparation

  1. Ensure that the environment is comfortably warm, as shivering during the recording may result in interference. Reassure the patient that recording a 12-lead ECG is a quick and painless procedure. A common misconception among patients is that they will experience an electric shock during the test, so it is important to offer a full explanation of the procedure.
  2. The operator will require unrestricted access to the chest, arms and lower legs in order to correctly place the monitoring electrodes. Operators must take steps to respect the sensitivities of the patient and provide a chaperone if necessary.
  3. The patient will be asked to lie in a recumbent on a bed, at about a 45° angle with the head supported by a pillow. Operators working in primary care settings may have to use an examination couch. 
  4. The operator must wash their hands before commencing

Skin preparation

The presence of excessive

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Risks and complications


Most ECG machines will alert the operator if an electrode becomes disconnected. If the signal fails from one or more electrodes, this will be seen as a straight line beside the affected ECG lead. Check the cables for disconnections or change the monitoring electrodes and the conduction gel may have dried out.


Artefact (or noise) is any recorded electrical activity that does not originate in the heart (Adam and Osborne, 2005). Artefact is generally muscular or electrical.

Muscle artefact

This is sometimes called somatic tremor. Any skeletal muscle movement can result in muscle artefact. Artefact from tremor is mainly seen on the limb leads with the electrodes on the arms most commonly affected (Hampton, 2008). The resultant ECG trace shows chaotic, wavy or bumpy waveforms. Possible causes include:

  • shivering or tremor
  • tension
  • dirty or corroded leads and connections 
  • dried electrode gel

This can be resolved by:

  • keeping the

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NMC proficiencies

Nursing and Midwifery Council: standards of proficiency for registered nurses

Part 1: Procedures for assessing people’s needs for person-centred care

2.1 take, record and interpret vital signs manually and via technological devices

2.3 set up and manage routine electrocardiogram (ECG) investigations and interpret normal and commonly encountered abnormal traces

2.5 manage and interpret cardiac monitors, infusion pumps, blood glucose monitors and other monitoring devices

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Adam SK, Osborne S. Critical care nursing: science and practice. 2nd edn. Oxford University Press, Oxford; 2005

Bailey JJ, Berson AS, Garson Jr A et al. Recommendations for standardization and specifications in automated electrocardiography: bandwidth and digital signal processing. Circulation. 1990;81(2);730-739. https://doi.org/10.1161/01.cir.81.2.730 

Hampton JR. 150 ECG P=problems. 3rd edn. London: Churchill Livingston; 2008

Kligfield P, Gettes LS, Bailey JJ et al. Recommendations for the standardization and interpretation of the electrocardiogram: part 1. Circulation. 2007;115(10):1306-1324. https://doi.org/10.1161/CIRCULATIONAHA.106.180200  

MacFarlane PW, Colaco R, Stevens K et al. Precordial electrode placement in women. Neth Heart J. 2003;11(3):118-122

Mason RE, Likar I. A new system of multiple-lead exercise
electrocardiography. Am Heart J. 1966;71(2):196–205. https://doi.org/10.1016/0002-8703(66)90182-7 

Metcalfe H. Recording a 12-lead electrocardiogram. Nursing Times. 2000;96(19):43-44

Pahlm O, Haisty Jr WK, Edenbrandt L et al. Evaluation of changes in standard electrocardiographic QRS waveforms recorded from activity-compatible proximal limb lead positions. Am J Cardiol. 1992;69(3):253-257. https://doi.org/10.1016/0002-9149(92)91315-u 

Riley J. The ECG: its

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