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The term syncope (Greek: synkope) literally means a “cessation,” a “cutting short,” or “pause.” Medically, it refers to an episodic loss of consciousness and postural tone and an inability to stand because of a diminished flow of blood to the brain. It is synonymous in everyday language with fainting. Feeling faint and a feeling of faintness are also commonly used terms to describe the loss of strength and other symptoms that characterize the impending or incomplete fainting spell. This latter state is referred to as presyncope. Relatively abrupt onset, brief duration, and spontaneous and complete recovery not requiring specific resuscitative measures are other typical features.

Faintness and syncope are among the most common of all medical problems. Practically every adult has experienced some presyncopal symptoms, if not a fully developed syncopal attack, or has observed such attacks in others. Description of these symptoms, as with other predominantly subjective states, is often ambiguous. The patient may refer to the experience as light-headedness, dizziness, a “drunk feeling,” a weak spell, or, if consciousness was lost, a “blackout. As most people have experienced presyncope before, they will usually be able to identify the sensation for what it is. In many instances the nature of the symptoms is clarified by the fact that they include a sensation of faintness and then a momentary loss of consciousness, which is easily recognized as a faint, or syncope. This sequence also informs us that under certain conditions any difference between faintness and syncope is only one degree. These symptoms must be clearly set apart from certain types of epilepsy, the other major cause of episodic unconsciousness, and from disorders such as cataplexy, transient ischemic attacks (TIAs), “drop attacks,” and vertigo, which are also characterized by episodic attacks of generalized weakness or inability to stand upright, but not by a loss of consciousness. What has emerged from large series is that cardiac syncope and syncope of unknown cause carry an increased risk of death and and vasovagal syncope, does not (Soteriades et al).


From a clinical perspective, syncope is essentially of three main types, all ultimately causing hypotension and each of which may lead to a temporary reduction in the flow of blood to the brain. To these is added a fourth category of miscellaneous causes of syncope.

The first, reflex withdrawal of vascular sympathetic tone (vasodepressor effect), is triggered by inhibition of the normal tonic sympathetic influences and is often associated with excessive vagal effect and bradycardia. The type associated with bradycardia is called vasovagal syncope, a form of neurogenic, or neurocardiogenic syncope, by which is meant the withdrawal of sympathetic tone through a reflex neural mechanism. Neurocardiogenic syncope usually signifies that the inciting stimulus originates in neural receptors within the heart.

The second is a failure of sympathetic innervation of ...

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