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ECGs 1: how to carry out monitoring

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The first in a three-part series on electrocardiograms explores continual monitoring

Author: Dan Higgins is senior charge nurse, critical care, University Hospitals Birmingham Foundation Trust

Citation: Higgins D (2011) ECGs 1: carrying out monitoring. Nursing Times; 107: 27, early online publication.

Keywords: ECG monitoring, Continual, Heart, Rhythm


An electrocardiogram (ECG) is a recording of the heart’s electrical activity (Huff, 2006). It has two approaches:

  • 12-lead ECG: This definitive diagnostic procedure measures electrical activity from a three-dimensional perspective;
  • Basic monitoring technique: This provides a less-detailed view of the basic heart rhythm and is performed as a continual process.

This first of a three-part series, this article explores the indications for continual ECG monitoring, how it is performed, and nurses’ responsibilities when caring for a patient being monitored. Part 2 will explore ECG rhythm analysis, while part 3 will look at the role of the 12-lead ECG.

Indications for ECG monitoring

ECGs can alert nurses to changes in a patient’s condition and aid diagnostic decisions (Jevon, 2009). Indications include:

  • Any acute critical illness;
  • Peri and post cardiac arrest;
  • Acute coronary syndromes;
  • History of life-threatening cardiac arrhythmias;
  • During and following any invasive cardiac procedure;
  • Any procedure involving sedation or anaesthesia;
  • Cardiovascular or conduction abnormalities, such as electrolyte or metabolic imbalance or drug overdose. 

Physiology of the heart

Electrical impulses are initiated from the sinoatrial node of the heart. They are conducted through the atrial muscle and the atrioventricular node, down the bundle of His, and through the right and left ventricles via the Purkinje fibres (Fig 1).

The conduction of electrical impulses is detected through the skin by placing electrodes at specific points. These impulses are displayed as a graphic waveform on an ECG machine or a cardiac monitor. Each part of the display relates to part of the conduction pathway and, providing no abnormality is present, the cardiac cycle (Fig 2).

  • The P wave represents the electrical impulse spreading across the atria, known as atrial depolarisation. This is associated with atrial contraction.
  • The QRS complex represents the electrical impulse conducted down the bundle of His, and into the right and left bundle branches and the Purkinje fibres. This is known as ventricular depolarisation and is associated with ventricular contraction.
  • T represents a repolarisation of the ventricles. This is associated with ventricular relaxation.

The ECG monitoring process

Before starting ECG monitoring, informed consent must be obtained.

Good contact between the electrode and the skin is essential so the skin should be clean and dry. If excess hair is present, a small patch can be shaved or trimmed with the patient’s consent. Skin oil and grease can be removed by rubbing the skin with alcohol or gauze (Navas, 2003). Electrodes are then attached to the patient according to the manufacturer’s instructions.

There are several configurations for electrode positions, including three-, five- and 10-lead set-ups. A standard three bipolar lead configuration is most commonly used for continual ECG monitoring. Bipolar lead monitoring can be used to track heart rate, observe basic arrhythmias, and to detect ventricular fibrillation (Drew et al, 2004). Electrode pads are placed below the right clavicle, the left clavicle and the left lower rib cage. The red cable is connected to the right clavicle electrode, the yellow cable is connected to the left clavicle electrode, and the green cable is connected to the lower ribcage electrode.

Recalling this configuration in urgent situations can be challenging for practitioners who do not use this skill frequently. It is important to remember that any configuration has the potential to demonstrate a trace for emergency analysis.

Using the standard three-lead set-up, the heart can be viewed (electrically) from a two-dimensional (bipolar) view using any two of the three electrodes. These views are known as leads I, II and III. The monitor is turned on and connected to the patient, and the lead to record is selected. Lead II tends to be the standard as it provides a good recording of atrial and ventricular activity, enabling cardiac arrhythmias to be identified (Endacott et al, 2009). The ECG will be displayed on the monitor. It should be checked for clarity, size of complexes and interference. Monitor settings, such as brightness and contrast, may require adjustment to optimise the display.

Common problems

If an ECG monitor alarm is triggered or if problems with waveforms are identified, the immediate course of action is to assess and treat the patient using the ABCDE approach outlined by the Resuscitation Council (UK) (2010). A flatline ECG trace is commonly caused by disconnection of a lead or electrode, but the patient may be asystolic or in cardiac arrest.

A patient may also display an ECG rhythm on a monitor but have no pulse. This is known as pulseless electrical activity and should be treated as an emergency as the patient is in cardiac arrest.

ECG electrodes should be changed frequently as the conductive gel can dry easily, affecting trace quality (Sharman, 2007). Electrode sites should be observed for signs of allergy, such as redness or itching. If an allergy is suspected, hypoallergenic electrodes should be used (Jevon, 2009).


Heart-rate alarms should be based on normal values for the patient. Alarms should be set for both high and low rates. 


To avoid poor-quality trace, electrode-to-skin contact should be checked to ensure the gel is moist. Leads should be positioned to avoid cable drag and skin should be dry.


This can be caused by other monitoring equipment and may be reduced by moving electrode positions or configuration. Some ECG monitoring systems also have electrical filters. If the trace is small, the gain (amplitude of the signal) can be increased. However, nurses should be cautious when doing this as some conditions, such as pericardial effusion, can cause a reduction in ECG voltage (Endacott et al, 2009).


Double counting of heart rate can occur
if waveform morphology is altered. Changing configuration or the positioning of electrodes may rectify this. The patient’s respirations can also cause interference with the waveform, resulting in a wandering baseline. This is usually rectified by changing the position of the electrode.

Patient care

Patients should be nursed in a high observation area. ECG monitoring can cause anxiety for them or their relatives, especially if alarms sound.

Alarms should be set appropriately and explained to the patient and family, and the rationale for ECG monitoring should be discussed. Patients and relatives are likely to “monitor watch”, so explaining acceptable values can reduce unnecessary panic. Patients should also be advised that activities, such as brushing teeth, are likely to cause emergency alarms to sound. Electrode repositioning and configuration can reduce the incidence of this.

Once monitoring has started, it is important to document certain details of the procedure (Box 1).

Box 1. Documentation

The following should be documented once ECG monitoring has commenced:

  • Indication for ECG monitoring
  • The date and time monitoring started
  • The lead configuration used
  • Skin preparation
  • Any rhythm rate abnormality
  • Action taken as a result of the analysis.

Following immediate assessment, any changes in ECG rate or rhythm should be reported as appropriate. If rhythm or waveform morphology changes, a diagnostic 12-lead ECG is usuallyindicated. NT

Key points

  • An ECG is a recording of the electrical activity of the heart. 12-lead or continual ECG monitoring can be performed
  • ECGs can highlight changes in a patient’s condition and aid diagnosis
  • The conduction of the heart’s electrical impulses is detected through the skin by electrodes placed at specific points and displayed as a graphic waveform on an ECG machine or cardiac monitor
  • A flatline ECG trace is often caused by a lead or electrode becoming disconnected
  • Patients on continual ECG monitoring should be nursed in high observation areas where alarms are easily heard
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