• Sudden cardiac death
• electrocardiography

Sudden cardiac death (SCD) is defined as an unexpected death due to cardiac causes occurring within 1 h of symptom onset in a person without any prior condition that would appear to be fatal. It represents a major public health problem affecting more than 500 000 patients annually in the USA, and accounts for approximately 50% of deaths from cardiovascular causes. The most common electrical mechanism leading to SCD is the interaction of a triggering event and an abnormal substrate that induces ventricular tachycardia (VT) degenerating (or not) into ventricular fibrillation (VF). Less frequently, SCD is initiated directly by VF or polymorphic VT. SCD associated with bradyarrhythmias or asystole, frequently expressing electromechanical dissociation, are less frequent, and usually occur in the setting of advanced heart failure1 (figure 1).

Cardiac arrest (CA) events can sometimes be resolved by resuscitating manoeuvres, thus preventing what would have been an SCD. Although strictly speaking this should be referred to as a CA episode, some refer to this as aborted SCD or simply as an SCD event. The vast majority of SCDs are due to a first arrhythmic event, although 10–15% of them are due to recurrent events. The prevention of a life threatening arrhythmic event in patients who survive a CA is referred to as ‘secondary prevention’. However, since sustained VT can also be lethal, prevention of SCD in patients who already had sustained VT (even if the VT did not cause the CA) are also included in the concept of secondary prevention of SCD and in some …