Ventricular fibrillation - Ventricular arrhythmias

Ventricular fibrillation

Definition

Chaotic electromechanical activity of the ventricles causing a loss of cardiac output.

Incidence

The most common cause of sudden death and the most common primary arrhythmia in cardiac arrest.

Aetiology

May occur de novo, as a sequelae to a myocardial infarction, post-electrocution or as a result of other arrhythmias or drug overdose including digoxin and adrenaline. It may be preceded by another arrhythmia such as torsades de pointes or develop in the context of complete heart block. Hypokalaemia and hypomagnesaemia may also result in ventricular fibrillation.

Pathophysiology

The underlying electrical activity consists of multiple ectopic foci and small re-entry circuits with resulting un-coordinated contractions such that cardiac ventricular filling and cardiac output fall to zero.

Clinical features

The clinical picture is of cardiac arrest with loss of arterial pulsation, loss of consciousness and cessation of breathing.

Investigations

ECG shows the chaotic rhythm with ventricular complexes of varying amplitude, rate and form distinguishing it from pulseless electrical activity and asystole (the other causes of cardiac arrest).

Management

Early defibrillation is the most important treatment, as the longer it is delayed the less likely reversion to sinus rhythm is possible. Cardiopulmonary resuscitation should be initiated to maintain organ perfusion until defibrillation can be given.

Prevention of recurrent of ventricular fibrillation is with antiarrhythmics usually amiodarone.

Increasingly automatic implantable cardiac defibrillators (AICDs) are implanted to prevent sudden death. The most common indication is for ‘failed sudden death’ where a subject is fortunate to survive such an event. It is now customary to use these in patients known to have a high risk of sudden cardiac death.