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Cardiac monitoring part 2: Recording a 12 lead ECG

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Phil Jevon

PGCE, BSc, RN, is resuscitation officer/clinical skills lead, Manor Hospital, Walsall


An ECG is a recording of the electrical activity of the heart. The 12-lead ECG is an essential diagnostic tool in the management and treatment of ischaemic heart disease (Jevon, 2000). When recording a 12-lead ECG it is important to ensure accuracy and standardisation in order to avoid misinterpretation of the ECG and mismanagement of the patient (Jevon, 2003). Heart disease of electrocardiographic origin should be avoided (Wagner, 2000).


Indications for recording a 12-lead ECG include (Jevon, 2003):

Chest pain;


Sometimes before a general anaesthetic;

Cardiac arrhythmias;


History of syncope;

After successful cardiopulmonary resuscitation (CPR).


Explain the procedure to the patient and gain informed consent;

Assemble the necessary equipment (Fig 1). Check that the ECG cables are not twisted as this may cause interference (Metcalfe, 2000);

Ensure the environment is warm and the patient is as relaxed as possible. If the patient is shivering or anxious, this may lead to a tremor and an unclear ECG trace;

Ask the patient to lie down in a comfortable position, preferably resting against a pillow at an angle of 45º (Fig 2). To help ensure standardisation and facilitate interpretation of serial ECGs, ensure the patient assumes an identical position at each recording;

Position the inner aspects of the patient’s wrists close to but not touching the waist;

Prepare the patient’s skin. Shaving and abrading the skin is not usually necessary if using wet gel electrodes. If using solid gel electrodes, clean and degrease the skin, and shave if necessary;

Following local protocols, attach the electrodes to the limbs and connect the limb leads (Figs 3 and 4):

Red to the inner-right wrist;

Yellow to the inner-left wrist;

Black to the inner-right leg, just above the ankle;

Green to the inner-left leg, just above the ankle.

Apply the electrodes to the chest and attach the chest leads (Jevon, 2003) (Fig 5):

V1 (white/red lead) to the fourth intercostal space, just to the right of the sternum;

V2 (white/yellow lead) to the fourth intercostal space, just left of the sternum;

V3 (white/green lead) midway between V2 and V4;

V4 (white/brown lead) to the fifth intercostal space, mid-clavicular line;

V5 (white/black lead) on the anterior axillary line, on the same horizontal line as V4;

V6 (white/violet lead) to the mid-axillary line, on the same horizontal line as V4 and V5.

Confirm the calibration signal on the ECG machine is at a standard setting, adhering to local protocols. The standard calibration is that 1mV equals one large square vertical deflection on the ECG and the standard paper speed is 25mm per second (Fig 6);

Ask the patient to lie still, relax and breathe normally;

Print out the 12-lead ECG following the manufacturer’s recommendations;

Inspect the ECG to ensure clarity. Repeat if necessary;

After a satisfactory 12-lead ECG has been recorded, disconnect the patient from the ECG machine, clear the equipment away and clean as necessary according to the manufacturer’s recommendations. If serial recordings will be required, electrodes may be left on the patient;

If not done electronically by inputting data into the machine, label the ECG with the patient’s name, date of birth, unit number, date and time of recording, ECG serial number and any other relevant information, for example if the patient had chest pain during the recording (Jevon, 2003). Any deviations from the normal recording of a 12-lead ECG should be clearly visible;

Ensure the ECG is reviewed and stored following local protocols.


The angle of Louis (sternal angle) can be used as a reference point for locating the second intercostal space:

Palpate the angle of Louis;

Slide fingers over to the right side of the patient’s chest and locate the second rib, which is attached to the angle of Louis;

Slide the fingers downwards to locate the second intercostal space;

Slide the fingers further down to locate the third and fourth ribs and the corresponding intercostal spaces.


Alternative chest lead placements are sometimes indicated (Jevon, 2003):

Right-sided placement can be used to establish right ventricular involvement in an inferior or posterior MI. The chest leads are labelled V3R to V6R and are reflections of the left-sided chest leads V3 to V6;

Posterior placement can be used if there is a suggestion of posterior MI. The chest leads are applied below the left scapula at the same level as the fifth intercostal space;

Higher or more lateral placement on the chest can be used in cases of suspected acute coronary syndrome but inconclusive ECG.

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