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Syncope is more prevalent than either epilepsy or dissociative (psychogenic) seizures and is
common across all age groups with an overall incidence of 10.5% over a 17-year period12.
Vasovagal syncope is most frequently encountered in adolescence, whereas syncope due to
cardiac causes becomes increasingly prevalent with advancing age. The annual incidence of
syncope in the elderly population in long-term care has been reported to be as high as 6%9.
Recurrence is not unusual, occurring in approximately 30% of patients, typically within the
first two years after symptom onset13. Recurrence is associated with increased morbidity,
such as fractures, subdural haematomas and soft-tissue injuries14, and impaired quality of
life11.

There are numerous causes of syncope, each resulting in inappropriate systemic hypotension
and critical cerebral hypoperfusion. The causes can be divided into two main groups, cardiac
and vascular.

Cardiac conditions that cause syncope may be either structural heart disease, such as aortic
stenosis, hypertrophic cardiomyopathy, right ventricular dysplasia, some forms of congenital
heart disease, severe ischaemic cardiomyopathy and left atrial myxoma, or arrhythmias, such
as ventricular tachycardia, ventricular fibrillation, Brugada syndrome, long-QT syndrome,
supraventricular tachycardia, atrioventricular block, and sinus node disease causing
bradyarrhythmia or asystole. Vascular causes include reflex syncope, such as
neurocardiogenic or carotid sinus hypersensitivity, situational syncope, for example, during
coughing15 or micturition, and postural syncope, including orthostatic hypotension or postural
orthostatic tachycardia syndrome (POTS).

Neurocardiogenic syncope
Neurocardiogenic syncope is the most common cause of syncope11 and has many synonyms
including vasovagal, reflex, vasodepressor and neurally mediated hypotension. It arises
through the provocation of inappropriate reflex hypotension, with a variable degree of
bradycardia, or even transient asystole. There is often a precipitating cause such as prolonged
standing in a warm environment, or fright, for example, venepuncture or the sight of blood.
There may be a family history of ‘fainting’ or recent addition of vasoactive medication
targeted at, for example, hypertension or ischaemic heart disease.

A typical attack commences with prodromal symptoms of nausea, clammy sweating, blurring
or greying visual impairment, lightheadedness, and ringing or roaring tinnitus. Occasionally,
visual and auditory hallucinations can be more complex, and involve figures or scenes16.
Many of these individual symptoms are difficult for patients to describe and their description
may be vague, but collectively the cluster of symptoms is characteristic. Subsequently, the
patient will look pale and be sweaty. Mydriasis, tachypnoea, bradycardia and acral
paraesthesia may be present. Muscle tone is reduced, causing the eyes to roll up, and the
patient to fall to the ground. In the horizontal position, skin colour, pulse and consciousness
usually return within a few seconds, and while the patient may feel briefly unwell, confusion,
amnesia and drowsiness are not prolonged. Injury and incontinence are rare but may occur.
Tongue biting in syncope of any cause is unusual, but frequently seen in epilepsy. The
presence of brief myoclonic jerks during a syncopal episode of any cause, observed in
approximately 15% of patients17,16, is often over-interpreted by witnesses, and occasionally
health professionals, leading to diagnostic confusion. Such myoclonic jerks are usually multi-
focal and are rarely rhythmic, prolonged or of large amplitude. Videotelemetric monitoring
shows that the myoclonic jerks rarely last longer than 1520 seconds16 and do not have an
EEG correlate, unlike true epileptic myoclonus. Rarely, manual and orofacial automatisms
may occur, even during the presyncopal stage18. If recovery from cerebral hypoperfusion is
delayed, for example if the patient is held in an upright position, a secondary anoxic
convulsive seizure may occur. These should not be classified as epileptic however.