Classifying syncope

• Classifying transient loss of consciousness (TLOC) guides diagnostic thinking.
• TLOC mainly consists of syncope, epileptic seizures and psychogenic attacks.
• Syncope is TLOC due to cerebral hypoperfusion.

An unambiguous definition of syncope is important for care, research and teaching purposes. Unfortunately, many published definitions described ‘syncope’ as a broad category of transient loss of consciousness (TLOC) but still appeared to use a much narrower concept, creating confusion. The ESC-classification from 2001 and subsequently distinguished between ‘transient loss of consciousness’, i.e. disorders sharing unconsciousness of short duration with a rapid and spontaneous recovery and syncope, the form of TLOC that is due to cerebral hypoperfusion. Adding the cerebral hypoperfusion element sets syncope apart from other forms of TLOC, mostly epileptic seizures and psychogenic attacks. We provide short descriptions of different forms of syncope and other forms of TLOC.