Syncope is an abrupt and transient loss of consciousness due to a sudden decrease in cerebral perfusion. It is the condition most commonly confused with epilepsy. Table 2.2 contrasts syncope with epilepsy.
Also, like epilepsy, syncope is a clinical diagnosis, for which an eye-witnessed account is essential. There are two main subtypes.
The main form of neurocardiogenic syncope is vasovagal syncope: this is the commonest cause of loss of consciousness. There is usually a clear precipitating factor, such as prolonged standing, a hot environment, fright, or the sight of blood. Vasovagal syncope typically begins with the prodrome of nausea, clamminess, sweating, tunnelling and loss of vision (blurred or black), light headedness, and tinnitus. The patient may look pale and sweaty. In the event itself, there is reduced muscle tone, causing the eyes to elevate and the patient to slump to the ground. There may be a few small-amplitude and brief myoclonic jerks during the anoxic phase, which may easily be misinterpreted as an epileptic seizure. Consciousness is usually regained within a few seconds. Amnesia, drowsiness, and confusion are usually only brief. Injury and incontinence occasionally occur, but lateral tongue biting is very unusual.
Fainting may be more severe if the patient is held upright, e.g., if confined to the small space in a toilet or airplane, causing delayed recovery of cerebral perfusion and a secondary anoxic convulsion.
An accurate history, including the circumstances of the attack and an eye-witnessed account, are usually sufficient to diagnose vasovagal syncope. A 12-lead ECG is the most useful investigation (to exclude other more serious causes of syncope); head-up tilt table testing can assist the diagnosis.
Whereas neurocardiogenic syncope is fairly benign, cardiac syncope is potentially fatal. Causes include either cardiac arrhythmias (e.g., Wolff-Parkinson-White syndrome, long QT syndromes) or structural heart disease (e.g., hypertrophic cardiomyopathy, aortic stenosis). These require an accurate history, a full neurological and cardiac examination, ECG, echocardiography, and even prolonged ECG monitoring (24-hour or embedded long-term monitoring).
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