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Content and Chapter Update: The Canadian Syncope Risk Score (CSRS) June 2021

The CSRS, and its supporting data, are presented in "Decision-Making and Risk Assessment." The CSRS is a tool to aid ED disposition decisions in patients with unexplained syncope, and in patients without clear evidence of a serious cause of syncope.

The chapter has also been updated to reflect additional information throughout.


Syncope or fainting is a symptom complex consisting of a brief loss of consciousness associated with an inability to maintain postural tone that spontaneously resolves without medical intervention with the person returning to their baseline neurologic condition. Syncope accounts for approximately 1% to 2% of ED visits each year and 1% to 6% of hospital admissions.1–4 Over a lifetime, the prevalence of syncope ranges from 10.5% to 19%.1,5 Syncope in the preceding year is the best predictor of recurrence.6 It can affect the young and the old, with the elderly having the greatest morbidity.7 Near syncope, a premonition of fainting without loss of consciousness, shares the same basic pathophysiologic process as syncope and carries the same risks.8–11


The final common pathway of syncope is the same regardless of the underlying cause: about 10 seconds of complete disruption of blood flow or nutrient delivery to both cerebral cortices or to the brainstem reticular activating system, or reduction of cerebral perfusion by 35% to 50%. Most commonly, an inciting event causes a drop in cardiac output, which decreases oxygen and substrate delivery to the brain. Cerebral perfusion and consciousness are restored by the supine position, the response of autonomic autoregulatory centers, or restoration of a perfusing cardiac rhythm.

The causes of syncope are numerous (Table 52-1). The most common causes of syncope identified in the Framingham Heart Study were vasovagal (reflex mediated, 21%), cardiac (10%), orthostatic (9%), medication related (7%), neurologic (4%), and unknown (37%).5 Even with exhaustive patient evaluation, the cause remains unknown in about 18% to 40% of individuals.12,13 After ED investigation, the unknown proportion may be 50% to 60%. Diagnosis is important, because each diagnostic classification carries with it prognostic risk.14 Cardiac syncope doubles the risk of death, neurologic syncope increases the risk of death by 50%, and syncope of unknown cause increases the risk of death by 30%.5 Individuals with neurally mediated, reflex-mediated or vasovagal syncope have no increased risk of death,5 but patients with recurrent syncope have an increased risk of injury.15

TABLE 52-1Causes of Syncope

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