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Syncope (derived from the Greek words, “syn” meaning “with” and the verb “koptein” meaning “to cut” or more appropriately in this case “to interrupt”) is a symptom defined as a transient, self-limited loss of consciousness, usually leading to falling. The onset of syncope is relatively rapid, and the subsequent recovery is spontaneous, complete, and usually prompt.

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Syncope is a common symptom, experienced by up to 30% of healthy adults at least once in their lifetime. Syncope accounts for 3% of emergency department visits and 1% of medical admissions to a general hospital. Syncope is the seventh most common reason for emergency admission of patients older than 65 years. The cumulative incidence of syncope in a chronic care facility is close to 23% over a 10-year period with an annual incidence of 6% and recurrence rate of 30%, over 2 years. The age of first faint, a commonly used term for syncope, is less than 25 years in 60% of persons, but 10% to 15% of individuals have their first faint after age 65 years.

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Syncope because of a cardiac cause is associated with higher mortality rates than syncope from other causes irrespective of age. In patients with a noncardiac or unknown cause of syncope, older age, a history of congestive cardiac failure, and male sex are important prognostic factors of mortality. It remains undetermined whether syncope is directly associated with mortality or is merely a marker of more severe underlying disease. Figure 57-1 details the age-related difference in prevalence of benign vasovagal syncope (faint) compared to other causes of syncope.

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Figure 57-1.
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Comparison of ages of first syncope in 443 patients with vasovagal syncope and 88 patients with syncope of other known causes.

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The temporary cessation of cerebral function that causes syncope results from transient and sudden reduction of blood flow to parts of the brain (brain stem reticular activating system) responsible for consciousness. The predisposition to vasovagal syncope starts early and lasts for decades. Other causes of syncope are uncommon in young adults, but much more common as people age.

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Regardless of the etiology, the underlying mechanism responsible for syncope is a drop in cerebral oxygen delivery below the threshold for consciousness. Cerebral oxygen delivery, in turn, depends on both cerebral blood flow and oxygen content. Any combination of chronic or acute processes that lowers cerebral oxygen delivery below the “consciousness” threshold may cause syncope. Age-related physiological impairments in heart rate, blood pressure, cerebral blood flow, and blood volume control, in combination with comorbid conditions and concurrent medications account for the increased incidence of syncope in the older person. The blunted baroreflex sensitivity with aging is manifested as a reduction in the heart rate response to hypotensive stimuli. Older adults are prone to reduced blood volume owing to excessive salt wasting by the kidneys as a result of a ...

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