Summary

Syncope is a transient loss of consciousness due to transient global cerebral hypoperfusion, characterised by rapid onset, short duration, and spontaneous complete recovery. [1] The onset of syncope is relatively rapid, and the subsequent recovery is spontaneous, complete, and usually prompt. [2] The most common causes of syncope are cardiovascular in origin and are associated with a high mortality in patients with underlying heart disease, transient myocardial ischaemia, and other less common cardiac abnormalities. [3] Syncope is distinct from vertigo, seizures, coma, falls, psychogenic pseudosyncope, drop attacks, transient ischaemic attacks, and states of altered consciousness. [4] Post-ictal confusion is one of the key differentiating factors for seizures.

Syncope evaluation accounts for 3% to 5% of patients presenting as an emergency, of whom 50% are admitted to hospital. [5] In an observational cross-sectional study of 305,932 patients, adjusted incidence rate of syncope varied between 0.80 and 0.93 per 1000 person-years and was unchanged over the years. Overall mortality has also remained the same at around 0.28%. [6] A cause for syncope is determined in 55% to 82% of cases. [7] [8] [9] In older patients admitted to hospital with syncope, non-cardiovascular causes (such as vasovagal or orthostatic episodes) are twice as common as cardiovascular causes (such as arrhythmias or ischaemia). [10]

Risk factor identification is the most important step in evaluating a patient with syncope. It is also critical to identify those with high risk of death - for example, people with structural heart disease or abnormal ECG. [11]

Differentiating between syncope and epileptic seizure can sometimes be challenging. Vasovagal syncope (VVS) is the most common type of syncope, including in children. [12] [1] Despite VVS being benign, quality of life may be severely affected in a significant proportion of highly symptomatic patients. A typical history of VVS is usually sufficient to make the diagnosis without any additional testing. VVS is usually preceded by a prodrome of symptoms such as dizziness, nausea, and diaphoresis. Situational factors such as prolonged standing, dehydration, fear, and pain also help in making the diagnosis of VVS. Twitching and jerking are often seen with vasovagal or cardiac syncope, which can be differentiated from rhythmic jerking of all the limbs in tonic-clonic seizures. Loss of bowel and bladder control, commonly seen with seizures, is rare during syncope. Further testing is required when the diagnosis remains uncertain. [13]