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result and any further action with the patient. To involve the patient in their care and provide assurance of a normal result or explain the actions to be undertaking in the event of an abnormal result. E,P

10 Wash and dry hands or decontaminate with alcohol handrub. To prevent crossinfection (Fraise and Bradley 2009, E).

Action Figure 5 Taking a pulse.

Problem-solving table 12.1 Prevention and resolution (Procedure guideline 12.1)

Postprocedural considerations

Documentation

The pulse should be recorded in the patient’s notes on the institution’s approved observation chart. The recording should be dated and timed so that the pulse trend may be viewed easily as part of ongoing patient monitoring.

Twelvelead electrocardiogram (ECG)

Definition

Electrical currents generated and transmitted through the heart also spread throughout the body and can be monitored and amplified with an instrument called an electrocardiogram (Marieb and Hoehn 2010).

A 12lead ECG is a quick noninvasive way of acquiring data to ascertain information about the electrophysiology of the heart (Marieb and Hoehn 2010). Electrical changes, which take place as the cardiac muscle contracts and relaxes, are recorded on the ECG trace and produce 12 different tracings from different combinations of limb and chest leads (Tortora and Derrickson 2009).

Anatomy and physiology

The starting point of the cardiac electrical cycle is the sinoatrial (SA) node. This is the heart’s natural pacemaker, which can create impulses at 60–100 beats per minute. Its ability to spontaneously generate and discharge an electrical impulse is called automaticity (Docherty 2005).

A typical ECG consists of a series of three distinguishable waves called deflection waves (see Figure 12.6). The first wave, the small P wave, lasting about 0.08 seconds, results from movement of the depolarization wave from the SA node through the atria. The impulse travels from the atria to the ventricles via the atrioventricular (AV) node through internodal tracts (Lemery et al. 2003): this is the PR interval. From the AV node, the impulse travels down the His–Purkinje system and throughout the ventricles. The septal area contracts before the main ventricle muscle (Tortora and Derrickson 2009), giving rise to a small negatively deflected Q wave on the ECG.

Figure 12.6 Normal electrocardiograms or ECG (lead II). Pwave = arterial depolarization; QRS complex = onset of ventricular depolarization; Twave = ventricular repolarization.

Reproduced from Tortora and Derrickson (2009).

The His–Purkinje system consists of the His bundle, right bundle branch, left bundle branch and Purkinje fibres (Tortora and Derrickson 2009). The Purkinje fibres conduct impulses through the muscle assisting depolarization almost simultaneously (Philip and Kowery 2001), giving rise to the positive Rwave deflection on the ECG, followed by an Swave as the ECG then detects the right ventricle muscle movement (Docherty 2005). The Twave illustrates ventricular repolarization, commonly referred to as the resting phase of the ventricles. Sometime a small Uwave preceding the Twave is noticeable and this represents relaxation of the ventricles (Chummun 2009). Atrial repolarization is not graphically represented on the ECG as it is hidden in the QRS complex (Sharman 2007).

Related theory

The first three leads or views of the heart (leads I, II and III) were introduced in 1902 by Willem Einthoven. Figure 12.7 illustrates the specific arrangement known as the Einthoven triangle together with normal ECG lead tracings (Einthoven 1902). In acute clinical areas where continuous cardiac monitoring is required, the three limb leads can be placed according to Figure 12.7 and the monitor is set to show lead II as this gives the best picture and is the most accurate atrial monitoring lead (Docherty 2002, Navas 2003b). An ECG lead records the difference in electrical potential between a negative and positive electrode.

Figure 12.7 Position of electrodes for 12lead ECG. Redrawn from Metcalf (2000) with permission.