Syncope is a symptom complex that is composed of a brief loss
of consciousness associated with an inability to maintain postural
tone that spontaneously and completely resolves without medical
intervention. It is distinct from vertigo, seizures, coma, and states
of altered consciousness.
Syncope accounts for approximately 1% to 2% of
ED visits each year and up to 6% of hospital admissions.1,2 It
is estimated that one in four people will faint during their lifetime,
it is often recurrent and can affect the young and the old, with
the elderly having the highest incidence and risk for morbidity.3,4 Near-syncope,
a premonition of syncope without loss of consciousness, shares the
same basic pathophysiologic process as syncope and likely carries
the same risks.
The final common pathway of syncope is the same regardless of
mechanism. A lack of blood flow or vital nutrient delivery to both
cerebral cortices or to the brainstem reticular activating system
for 10 to 15 seconds will lead to loss of consciousness and postural
tone. A reduction of cerebral perfusion by 35% or complete
disruption for 5 to 10 seconds will cause symptoms. Most commonly,
an inciting event causes a drop in cardiac output, which decreases
oxygen and substrate delivery to the brain.5 Less
commonly, vasospasm or other alterations in flow reduce central nervous
system blood flow. The reclined posture assumed after syncope, the
response of autonomic autoregulatory centers, or reversion to a
perfusing cardiac rhythm will reestablish cerebral perfusion, leading
to a spontaneous return of consciousness.
The causes of syncope are numerous, from common benign disorders to life-threatening processes (Table 56-1).
In the Framingham Heart Study, 7814 patients were followed for 17
years, and 822 reported syncope. The causes determined in the study
were: vasovagal (often called reflex mediated)
(21%), cardiac (10%), orthostatic (9%),
medication related (7%), seizure (5%), neurologic
(4.1%), and unknown (37%).6 In
most studies even with exhaustive evaluation the unknown cause remains
around 40%.7,8 After limited ED investigation
the unknown proportion may be 50% to 60% at the
time of discharge.9,10 If a diagnosis can be made,
it is important, as each diagnostic classification carries with
it prognostic risk. For example, in the Framingham study those with
documented heart disease and syncope had twice the rate of death
of patients without syncope, and those with syncope with a neurologic
cause were 50% more likely to die. Those with an unknown
cause also had a significant increased risk of death of 30%,
whereas those with neurally mediated or vasovagal syncope had a
lower risk of death than the general population cohort of the study.
Table 56-1 Causes of Syncope |Favorite Table|Download (.pdf)
Table 56-1 Causes of Syncope
|Structural cardiopulmonary disease||Vasovagal|
|Valvular heart disease||Situational|
|Congenital heart disease...|
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