In most patients, syncope is due to simple fainting (vasovagal syncope) and is benign. However, syncope may also be the presentation of life-threatening illness. It is essential to recognise patients with syncope who are at high risk of cardiac events. Most of these can be successfully treated, but they must be diagnosed and managed in a timely manner.
- Syncope is defined as a transient loss of consciousness due to cerebral hypoperfusion, characterised by rapid onset, short duration and complete spontaneous recovery. The mechanism of cerebral hypoperfusion is usually hypotension.
- All patients presenting with syncope should be classified as either high or low risk of a malignant cardiac cause.
- In most patients, the cause of syncope can be diagnosed from a detailed history, physical examination, postural blood pressure measurements and a 12-lead ECG.
- Vasovagal syncope (fainting) is the most common cause of syncope in all age groups.
- Patients with syncope in the setting of structural heart disease or an abnormal ECG are at high risk of cardiac syncope, and require prompt investigation.
- Patients with syncope during exercise (rather than after cessation of exercise) are at high risk of adverse cardiac events, such as sudden death.