SETTING UP ECG MONITORING

The following measures should be observed when setting up ECG monitoring (Jevon 2009):

Correct chest and limb electrode placement (Fig. 4.2) is crucial for obtaining accurate information from any monitoring lead (Thompson 2010). The electrode placement and monitoring lead selected for ECG monitoring will depend on the following factors:

• Monitoring system (e.g. three- or five-wire monitoring system). If a five-wire system is being used a suggested ECG electrode placement is red (right shoulder), yellow (left shoulder), green (left lower thorax/hip region), black (right lower thorax/hip region) and white on the chest in the desired V position, usually V1 (Jevon 2009). If a three-wire system is being used a suggested ECG electrode placement is red (right shoulder), yellow (left shoulder) and green (left lower thorax/hip region), although this system is much less commonly used in clinical practice.
  
• Goals of monitoring, e.g. if arrhythmia diagnosis is the goal.
  
• Patient’s clinical situation, e.g. in cardiopulmonary resuscitation, the precordium should be left unobstructed in case defibrillation is required (Resuscitation Council UK 2010).

Fig. 4.2 Suggested ECG electrode placement using a five-wire monitoring system.

EASI 12-Lead ECG Monitoring

The conventional 12-lead ECG using 10 electrodes attached to the limbs and chest is recognised as the current medical standard for the identification, analysis and confirmation of many cardiac abnormalities including cardiac arrhythmias and cardiac ischaemia/infarction.

If 12-lead ECG monitoring is undertaken on a continual basis, the benefits include:

• Facilitating the accurate recognition of cardiac arrhythmias
  
• Enabling the monitoring of the mid-precordial leads which is particularly important for the detection and management of ischaemia
  
• Enabling the recording of transient ECG events of particular diagnostic or therapeutic importance
  
• Enabling the differentiation between post-PTCA (percutaneous transluminal coronary angioplasty) ischaemia and occlusion.

Unfortunately the use of a conventional 12-lead ECG system using 10 electrodes for continuous cardiac monitoring is cumbersome and generally not practical in the clinical area. However, the EASI system, a new concept in 12-lead ECG monitoring, requires the use of only 5 electrodes (Fig. 4.3):

• E electrode on the lower sternum at the level of the fifth intercostal space
  
• A on the left midaxillary line on the same level as the E electrode
  
• S electrode on the upper sternum
  
• I on the right midaxillary line on the same level as the E electrode..

Fig. 4.3 EASI 12-lead ECG monitoring system.

(Reproduced by permission of Philips.)

A fifth ground electrode can be placed anywhere.

The EASI system for 12-lead ECG monitoring using only 5 electrodes is less cumbersome and more practical than the standard 10-electrode system. It is therefore more comfortable for the patient. In addition it will not interfere with such procedures as cardiac auscultation, cardiopulmonary resuscitation (CPR), defibrillation and echocardiography.

POTENTIAL PROBLEMS WITH ECG MONITORING

There are potential problems that can occur when undertaking ECG monitoring and it is important to realise that standardisation is possible only if the ECG is performed in a standard way each time (Thompson 2010). It has been identified in the literature that there is a wide variation in the identification of correct lead placement (McCann et al. 2007) leading to inaccurate diagnosis and patients being exposed to potentially harmful therapeutic interventions (Rajaganeshan et al. 2008). Potential problems that may be encountered include the following.

The ‘Flat-Line’ Trace

Check the patient immediately. However, the most likely cause is mechanical. Check:

• the condition of the patient
  
• that the correct monitoring lead is selected (usually lead II)
  
• that the ECG gain is set correctly
  
• that the electrodes are ‘in date’ and the gel sponge is moist, not dry
  
• that the electrodes are properly connected
  
• that the leads are plugged into the monitor.

Poor-Quality ECG Trace

If the ECG trace quality is poor, check:

• all the connections
  
• the brightness display
  
• that the electrodes are ‘in date’ and the gel sponge is moist, not dry (Jevon 2009)
  
• that the electrodes are properly attached.

If there are still difficulties obtaining a clear ECG trace, wiping the skin with an alcohol wipe may help. As electrodes tend to dry out after about 3 days, they should be changed at least that often although every 24 hours may be optimum to maintain skin integrity (Perez 1996).

Interference and Artefacts

Poor electrode contact, patient movement and electrical inter­ference, e.g. from bedside infusion pumps, can cause a ‘fuzzy’ appearance on the ECG trace. Interference can be minimised by applying the electrodes over bone rather than muscle (Resuscitation Council UK 2006). The patient should also be reassured and kept warm.

Wandering Baseline

A wandering baseline (ECG trace going up and down) is almost always caused by poor electrode contact to the skin (Thompson 2010). If respiration is the cause and the problem is not transient, serial ECG recordings should be taken in both inspiratory and expiratory phases (Thompson 2010).

Small ECG Complexes

Sometimes the ECG complexes may be too small and unrecognisable. Possible causes include pericardial effusion, obesity and hypothyroidism. However, sometimes it can be caused by a technical problem. Check that the ECG gain is correctly set and that lead II is being monitored. Repositioning the electrodes or selecting another monitoring lead sometimes helps (Jevon 2009).

Incorrect Heart Rate Display

If the ECG complexes are too small, a false low heart rate may be displayed. Large T waves, muscle movement and interference can be mistaken for QRS complexes, resulting in a false high heart rate being displayed. The nurse must be alert to the possibility of inaccurate heart rate readings, which can in particular be caused by poor electrode contact and interference (Jevon 2009). To minimise the potential for inaccuracies, a reliable good-quality ECG trace should be obtained.

Skin Irritation

ECG electrodes can cause skin irritation and contact dermatitis has been well reported in the literature (Rühlemann et al. 2010). The electrode sites should be regularly examined and if the patient’s skin appears irritated select another electrode placement.

False Alarms

Frequent false alarms will undermine the rationale for setting alarms and can also cause undue anxiety for the patient. It is important to ensure that the alarms are correctly and sensibly set and that the ECG is accurate, reliable and of a high standard.

THE ECG AND ITS RELATIONSHIP TO CARDIAC CONTRACTION

The ECG functions in four stages as follows (Fig. 4.4):

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