Ventricular fibrillation

Ventricular fibrillation is often referred to as chaotic and uncoordinated electrical activity; it is triggered by thousands of ventricular foci discharging at different and rapid rates (shown in Figure 8.4). The lack of a strong ventricular contraction causes circulatory collapse and loss of consciousness.

Causes

• Myocardial ischaemia (may occur after myocardial infarction or be associated with a prolonged QT interval)

• Electrolyte disorders such as potassium

• Cardiomyopathy

• Accidental electrical shock

• Digoxin toxicity

• Hypothermia

Fig. 8.4 Ventricular fibrillation.

Clinical features

The patient will experience a loss of consciousness, become pulseless and cease breathing.

Characteristic features of the ECG

• P wave and PR interval are unrecognisable.

• QRS rate and rhythm are not definable.

• QRS complex is not discernible.

• There is a wavy line composed of different waves whose amplitude and appearance are variable.

• In the early stages of VF the appearance is coarse but after some minutes it becomes progressively smaller or 'fine VF'. Fine VF can resemble asystole; to distinguish this, increase the gain on the monitor or review the rhythm in a different lead.

Response

Follow the algorithm for VF and aim to defibrillate the casualty within three minutes of collapsing once cardiac arrest has been confirmed.

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