Atrial fibrillation

Atrial fibrillation (AF) is one of the most common dysrhythmias with a prevalence of 1-1.5%, a figure that increases with advancing age. AF is characterised by erratic, disorganised and chaotic atrial activity that is associated with an irregular ventricular response which helps maintain cardiac output. The rhythm is triggered by multiple atrial ectopic foci stimulated at a frequency of 350-600 beats per minute outside the SA node region (Goodacre & Irons 2002). However, conduction down the His-Purkinje system is random and intermittent, resulting in an irregular ventricular response noted in the ECG. Since atrial contractions are weak, the potential for pooling and thrombus formation is strong, particularly in those who have experienced AF for more than 24 hours (Hand 2002).

The ERC (2001) treatment guidelines on peri-arrest arrhythmias classify AF according to whether it is high, intermediate (see Figure 8.8) or low risk. This division depends on the rate of AF and the presenting signs and symptoms.

Table 8.2 Atrial fibrillation risk.

Intermediate risk

High risk

• Heart rate 100-150

• Heart rate greater than 150bpm

• Dyspnoea

• Ongoing chest pain

• Poor tissue perfusion

• Critical tissue perfusion

Fig. 8.8 Atrial fibrillation.

Causes

• Digoxin toxicity

• Post valve surgery

• Hypertension

• Increased sympathetic activity

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