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    Last Updated Nov 01, 2018
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    • Syncope is a sudden transient loss of consciousness (LOC) with spontaneous complete recovery. Near syncope is considered equivalent to syncope.
    • 7-day risk of serious adverse outcome is 10% and death is 1/2501.
    • Despite several risk stratification rules (below),  the best diagnostic tools remain: careful history, thorough physical exam, and ECG and good clinical judgement.

    Pathophysiology, history, and physical exam


    Mortality >10% at 6 months.

    • Arrhythmias: Most common cause of cardiac syncope.
      • No prodrome.
      • Sudden LOC and may report palpitations prior to the event.
      • Occurs in any position.
      • Family history of arrhythmia, inherited cardiac disorders, sudden unexplained cardiac death, drowning, unexplained seizures.

    Syncope in the setting of exercise is due to cardiac arrhythmia until proven otherwise.

    • Structural lesions:
      • Valvular and cardiomyopathies: murmurs or signs of CHF require further workup – often need echocardiogram.
      • Pulmonary emboli unlikely to present as an isolated syncope given that if there is enough clot burden to obstruct the blood flow, there should be other findings such as SOB, tachycardia, ECG changes.
    • Ischemia: Infrequent cause (<3%) and often will have concomitant findings (such as massive STEMI on ECG or classic CP).


    Autonomic system fails to maintain blood pressure with increased heart rate.  Often have positional component, such as onset when standing up from sitting position.

    • Orthostatic vital signs neither sensitive nor specific and cannot be used in isolation to rule in or out this as cause of syncope.
    • Medications: Antihypertensives, diuretics, antidepressants, beta-blockers, alpha-blockers.
    • Postprandial hypotension: onset shortly after a meal.
    • Intravascular volume loss: dehydration (vomiting, diarrhea, decreased po intake), hemorrhagic (GI, occult trauma, AAA, splenic rupture, retroperitoneal bleeds, etc).

    *** SO MAY NOT BE THAT BENIGN AFTER ALL –> thorough exam, including rectal for melena and bedside US for AAA, in appropriate settings and in elderly/high-risk patients


    Autonomic system acts inappropriately resulting in reflex bradycardia and vasodilation. Benign cause of syncope with excellent prognosis.

    • Vasovagal: prodrome, induced by emotion or pain.
    • Situational: cough, micturition, defecation.
    • Carotid sinus hypersensitivity: older, male, stimulation of carotid sinus (necktie, shaving, etc).


    Transient interruption of blood flow to the brain stem or cerebral cortex.

    • Isolated syncope is rare (<1%).
    • Routine use of CT head for syncope is not indicated.
    • TIA and SAH patients have additional symptoms such as headache (SAH) and/or posterior circulation neurological findings (vertebrobasilar TIA).
    • Subclavian steal syndrome – stenotic subclavian artery receives additional blood from the vertebral artery drawing it away from the brainstem. There often will be a difference in the blood pressure in each arm and additional posterior circulation deficits. Patient may report using the affected arm prior to the syncope.



    Only mandatory test for all syncope patients.

    • Ottawa group found that the patients were at risk for cardiac outcome within 30 days if any of the following were present: (see below related resources)
    • Ottawa ECG Criteria3:
      • High degree blocks (2nd degree type II or 3rd degree AV)
      • Bundle branch + 1st degree block
      • RBB + left anterior or posterior block
      • Ischemic changes
      • Non-sinus rhythm
      • Left axis deviation
      • ED cardiac monitor abnormalities

    Other Investigations2

    • Investigations beyond ECG are required in cases where serious etiology is suspected or where it is not possible to determine the exact cause of syncope based solely on history and physical exam. These may include blood work, CXR, echocardiogram, telemetry, or Holter monitoring. The choice of the investigations is based on the presentation.

    Risk Stratification Tools

    Most risk stratification rules either have significant limitations or are awaiting validation. The Canadian Syncope Risk Score is currently awaiting validation. Perhaps the most studied is San Francisco Syncope Rule:

    San Francisco Syncope Rule Criteria4

    Congestive Heart Failure History

    Hematocrit < 30%

    ECG Abnormal?

    Shortness of Breath History

    Systolic BP < 90 mmHg at Triage

    Important: Pooled sensitivity was 86%.  1.4% of patients who are San Francisco Rule negative will have an adverse event at 7 days. Majority (60%) of missed diagnosis were arrhythmias. Also the rule did not exclude patients for whom the cause of the syncope was obvious, therefore making it unclear if this can be applied to undifferentiated syncope patients1.

    Canadian Syncope Risk Score 

    Important: Apply this score when there is a doubt as to potential etiology of syncope. The score predicts adverse events in the next 30 days (versus 7 days in San Francisco Rule). Patients with high score will require further evaluation5.

    Quality Of Evidence?


    Approach to the syncope in ED: Based on expert opinion.


    Use of the decision rules:  Much of the data used in the derivation of the decision rules is retrospective and/or chart reviews. San Francisco Syncope Rule had poor sensitivity of 86% and Canadian Syncope Rule is still awaiting validation.


    Related Information

    Reference List

    Relevant Resources


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