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Key Clinical Questions

  • image How should the history, physical examination, and electrocardiogram be utilized to direct further testing or limit further testing in the evaluation of syncope?

  • image What diagnostic testing should be considered for common causes of syncope?

  • image When do patients require hospital admission for syncope?

  • image What are the indications for advanced noninvasive or invasive tests in the evaluation of syncope?


Syncope is a sudden, transient loss of consciousness and postural tone with rapid onset and spontaneous recovery due to reduced perfusion to the brain’s reticular activating system. Other causes of unconsciousness resulting from etiologies other than transient cerebral hypoperfusion should not be classified as syncope. Syncope can cause physical injuries, impact quality of life, and be a predictor of adverse cardiovascular outcomes.


Syncope has a 3% incidence in the general population and 6% incidence in persons over age 75 years. It is responsible for 1% of emergency department (ED) visits, with more than 30% of ED syncope patients admitted, representing at least 2% of all hospital admissions. Older patients have higher rates of hospitalization and morbidity. The median cost of hospitalization of patients with syncope is approximately $8700, and up to 50% are discharged from the hospital without a specific diagnosis that caused the syncopal episode.

Syncope can present various diagnostic challenges, as many episodes of transient loss of consciousness may occur as unwitnessed events and with limited available history. Many testing modalities are also available in the evaluation of syncope, and judicious selection as well as timing and order of the most appropriate modalities can be challenging. However, following extended systematic evaluation (including outpatient evaluation when indicated), less than 20% of patients diagnosed with syncope will remain with a final diagnosis of unknown cause.

Estimates of syncope recurrence suggest that prior syncope, psychiatric illness, and age less than 45 years confer a higher risk of recurrent syncope. Surprisingly, severities of presentation, structural heart disease, and tilt table test response have no predictive value on syncope recurrence. Carotid sinus syndrome (CSS), the association of a syncopal event or events with carotid sinus hypersensitivity, has the highest prevalence (43%) in a population of patients presenting with recurrent syncope to the ED.


Transient hypoperfusion of the brainstem or both cerebral hemispheres can result from either decreased cardiac output or significant decrease in peripheral vascular resistance. These two mechanisms form the basis of the pathophysiology behind all syncopal events (Figure 101-1). Specific diagnoses may then be derived based on symptoms, signs, and additional testing.

Figure 101-1

Pathophysiologic basis of syncope. ANS, autonomic nervous system; BP, blood pressure; PE, pulmonary embolus; PPH, primary pulmonary hypertension.

In patients with traumatic injury (eg, coup-contrecoup or ...

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