Symptoms and signs of syncope: a review of the link between physiology and clinical clues.

Detailed history taking is of paramount importance to establish a reliable diagnosis in patients with transient loss of consciousness. In this article the clinical symptoms and signs of the successive phases of a syncopal episode are reviewed. A failure of the systemic circulation to perfuse the brain sufficiently results in a stereotyped progression of neurological symptoms and signs culminating in loss of consciousness; when transient, this is syncope. Prior to loss of consciousness the affected individual tends to exhibit unclear thinking, followed by fixation of the eyes in the midline and a 'frozen' appearance. Narrowing of the field of vision with loss of colour vision ('greying' out) and finally a complete loss of vision (hence 'blacking' out) occurs. Hearing loss may occur following loss of vision. This process may take as little as approximately 7 s in cases of sudden complete circulatory arrest (e.g. abrupt asystole), but in other circumstances it may take longer depending on the rate and depth of cerebral hypoperfusion. Complete loss of consciousness occurs with the 'turning up' of the eyeballs. Profound cerebral hypoperfusion may be accompanied by myoclonic jerks.