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A 20-year-old college wrestler comes to your office with his mother because she is concerned that he has "passed out" in church. While attending Sunday services during the summer, he has twice become dizzy while standing and slumped to the floor. He was briefly "out of it" but revived quickly when taken outside. On each occasion, he insisted on completing the religious service.

  • What questions would you ask to further define these episodes?
  • How would you classify these episodes to determine their likely cause?
  • Can you make a definite diagnosis based on history?
  • What questions help distinguish benign episodes from life-threatening ones?

Syncope is a syndrome of sudden, brief loss of consciousness and postural tone with spontaneous, complete recovery resulting from transient global cerebral hypoperfusion. Syncope may be associated with injury due to loss of consciousness or sudden death from an underlying cardiac cause. It is very common, accounting for up to 3% of emergency department visits and 6% of hospital admissions.1 Syncope is usually benign and most often caused by a vasovagal episode. Patients typically complain of "fainting," "passing out," falling out," a "dizzy spell," "blackout," "fall," or "collapse." The historian must distinguish syncope from other forms of dizziness such as presyncope, vertigo, disequilibrium, and vaguely described "light-headedness" or "giddiness" (see Chapter 6, Dizziness). Seizures, metabolic disturbances (eg, hypoglycemia), and concussion must be distinguished from syncope and do not result from temporary global cerebral hypoperfusion.

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Neurally mediated syncope, neural reflex syncope, vasodepressor syncope, neurocardiogenic syncope

Interchangeable terms for syncope primarily involving neural or reflex mechanisms.

Examples include vasovagal, situational, and carotid sinus syncope.

Situational syncopeSyncope associated with specific activities (eg, micturition, defecation, coughing, and swallowing).
Vasovagal syncopeThe common faint, the most common neural reflex disorder causing syncope.
Syncope mimicsDisorders characterized by loss of consciousness (LOC) that is either prolonged (ie, not transient) or does not result from cerebral hypoperfusion (eg, seizures, hypoxia, hypercapnia, intoxications, etc).
PseudosyncopePsychogenic (syncope associated with psychiatric disease)

Most patients with a simple fainting spell, or vasovagal syncope, do not seek medical attention. Etiologies of syncope vary depending on the clinical setting, study population, definition of syncope, and rigor of the diagnostic evaluation. For instance, psychiatric disease generally causes "pseudosyncope," not true syncope; nevertheless, it is classified as syncope in a number of studies. In general, syncope is classified into the following major categories:

  • Reflex (neurally) mediated syncope
  • Orthostatic hypotension
  • Cerebrovascular disease (a rare cause of syncope)
  • Medication-induced syncope
  • Cardiac syncope (due to organic heart disease and arrhythmias)
  • Syncope due to an unknown cause

Recent studies have classified fewer patients with syncope as having an unknown cause, probably due to more extensive diagnostic evaluation. In a Swiss study of patients with syncope presenting to an emergency department, the causes were as follows: vasodepressor (37%), orthostatic hypotension (24%), carotid sinus hypersensitivity (1%), neurologic (5%), ...

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