II. Definitions

  1. Syncope
    1. Rapid onset of transient loss of consciousness
    2. Inability to maintain postural tone
    3. May be associated with a fall
    4. Resolves spontaneously and quickly without intervention
  2. Presyncope (Near-Syncope)
    1. Weakness, Dizziness, Light Headedness or "graying out" of consciousness without loss of postural tone
    2. Evaluate Presyncope with the same vigor as Syncope
      1. Presyncope has the same risks of adverse event as Syncope
      2. Grossman (2012) Am J Emerg Med 30(1): 203-6 +PMID:21185670 [PubMed]

III. Epidemiology

  1. Up to one third of Syncope cases are idiopathic
  2. Common diagnosis
    1. Occurs in up to 40-50% of adults, and 75% over age 75
    2. Accounts for 1 to 1.5% of ER visits and up to 6% of admissions (250,000 admissions annually)

IV. Precautions

  1. Careful history (including from bystanders), exam, and ekg should direct limited diagnostics and disposition
  2. Always consider serious cause differential diagnosis (see rule of 15s below)
  3. Near-Syncope should be evaluated with the same thoroughness as Syncope (causes are the same)
    1. Bastani (2019) Ann Emerg Med 73(3): 274-80 [PubMed]

V. Pathophysiology

  1. Decreased global cerebral perfusion (usually on standing)
  2. Two key mechanisms
    1. Systemic vasodilation (Reflex Mediated Syncope)
    2. Decreased Cardiac Output (Cardiac Syncope, Orthostasis)

VI. Risk Factors

  1. Elderly
  2. Structural heart disease (e.g. Aortic Stenosis)
  3. Congestive Heart Failure
  4. Coronary Artery Disease

VII. Causes: Neural or Reflex Mediated Syncope (no Cardiovascular Risk, most common in all ages, 45% of cases)

  1. Vasovagal Syncope (Vasodepressor Syncope)
  2. Situational Syncope
    1. Micturition Syncope or with Defecation
    2. Cough Syncope (or sneezing)
    3. Valsalva (brass instrument playing, weight lifting)
    4. Hyperventilation
  3. Carotid Sinus Syncope
  4. Glossopharyngeal neuralgia (uncommon)
    1. Syncope occurs with Swallowing, talking, sneezing
  5. Trigeminal Neuralgia

VIII. Causes: Orthostatic Syncope (Orthostatic Hypotension Syncope, 10% of causes)

  1. See Orthostatic Hypotension
  2. Hypovolemia
    1. Acute Hemorrhage (Gastrointestinal Bleeding, Ectopic Pregnancy)
    2. Gastrointestinal losses (Vomiting, Diarrhea)
    3. Insufficient fluid intake
  3. Medication-related Syncope (Drug-Induced Syncope, responsible for 5-15% of Syncope causes)
    1. See Medication Causes of Orthostatic Hypotension
    2. See Medication Causes of Excessive Daytime Sleepiness
    3. See Bradycardia due to Medications
    4. See Prolonged QT Interval due to Medication
  4. Recreational drug use
    1. Alcohol
    2. Ecstasy (MDMA)
    3. Methamphetamine
  5. Postural Tachycardia Syndrome (POTS)
    1. Most common in female young women (associations with chronic Fatigue and Mitral Valve Prolapse)
  6. Autonomic failure
    1. See Autonomic Dysfunction
    2. See Diabetic Autonomic Neuropathy

IX. Causes: Cardiac Syncope (10-30% of causes, high risk conditions)

  1. Background
    1. Results from decreased Cardiac Output from Arrhythmia, structural heart disease or vascular event (e.g. Pulmonary Embolism)
    2. More likely in known cardiovascular disease (e.g. CAD, CHF, Atrial Fib), first episode after age 35 years
    3. Associated with no prodrome or prodromal Chest Pain or Shortness of Breath or Cyanosis
    4. Albassam (2019) JAMA 321(24): 2448-57 [PubMed]
  2. Predisposing cardiac conditions
    1. Wolff-Parkinson-White Syndrome (WPW Syndrome)
    2. Brugada Syndrome
    3. Hypertrophic Cardiomyopathy
    4. Arrhythmogenic Right Ventricular Dysplasia (ARVD)
    5. Prolonged QT Interval
  3. Arrhythmias
    1. Ventricular Tachycardia
    2. Sick Sinus Syndrome
    3. Supraventricular Tachycardia
    4. Atrioventricular Block (second or third degree)
    5. Pacemaker malfunction
  4. Valvular disorders
    1. Hypertrophic Cardiomyopathy (esp. young patients)
    2. Aortic Stenosis
    3. Acute Mitral Valve Regurgitation (i.e. acute MI with papillary Muscle rupture)
    4. Prosthetic Heart Valve complication (e.g. Thromboembolism, valvular obstruction)
  5. Vascular disorders
    1. Myocardial Infarction
    2. Aortic Dissection
    3. Abdominal Aortic Aneurysm rupture
    4. Pulmonary Embolism
    5. Pulmonary Hypertension
    6. Subarachnoid Hemorrhage
      1. Vermeulen (2007) Stroke 38(4): 1216-21 +PMID: 17322078 [PubMed]
    7. Subclavian Steal Syndrome
  6. Myocardial disorders
    1. Hypertrophic Cardiomyopathy
    2. Atrial Myxoma

XII. History: Preceeding or provocative event

  1. Prolonged standing
    1. Vasovagal Syncope
    2. Orthostatic Syncope
  2. Immediately on standing
    1. Orthostatic Hypotension
  3. While lying supine
    1. Cardiovascular Syncope (higher risk)
  4. With exertion (high risk for serious cause)
    1. See Exertional Syncope
    2. Aortic Stenosis
    3. Coronary Artery Disease or Coronary Artery Abnormalities
    4. Cardiomyopathy (e.g. Hypertrophic Cardiomyopathy, Myocarditis)
    5. Arrhythmia (e.g. ARVD, Long QT Syndrome, WPW Syndrome, Brugada Syndrome)
    6. Miscellaneous Causes (e.g. Heat Stroke, Hypoglycemia, Hyponatremia)
  5. After exertion in an athlete
    1. Vasovagal Syncope
  6. Valsalva (cough, Swallowing, eating, laughing, urinating or stooling)
    1. Reflex-mediated Syncope
  7. Neck rotation or pressure (e.g. tight collar)
    1. Carotid Sinus Hypersensitivity
  8. Use of arms
    1. Subclavian Steal Syndrome
  9. Stressful event
    1. Vasovagal Syncope

XIII. History: Associated symptoms during event

  1. Nausea, chills and sweats
    1. Vasovagal Syncope
  2. Aura
    1. Migraine Headache
    2. Seizure Disorder
  3. No prodromal symptoms (see below)
    1. Cardiovascular Syncope (higher risk)
    2. Although prodromal Dyspnea or Chest Pain also has been associated with Cardiac Syncope
  4. Slumping
    1. Coronary Artery Disease
    2. Arrhythmia
  5. Kneeling
    1. Orthostatic Hypotension
  6. Brief loss of consciousness (<30 to 60 seconds)
    1. Arrhythmia
  7. Loss of consciousness (>1 to 5 minutes)
    1. Seizure Disorder (esp. if postictal period)
    2. Neurologic, metabolic, or infectious cause
  8. Tonic-clonic movements
    1. Seizure Disorder
      1. Movements occur before fall and last longer than 30 seconds
      2. Followed by postictal period of confusion
    2. Syncope (esp. Vasovagal Syncope)
      1. Movements occur after syncopal fall in 90% of cases
      2. Appear as Myoclonic Jerks (but brief, <10 movements, and no postictal period)
  9. Focal neurologic deficits
    1. TIA or CVA (although LOC requires significant CNS involvement, for which resolution would be delayed)
    2. Todd's Paralysis (Seizure)
  10. Severe Thunderclap Headache
    1. Subarachnoid Hemorrhage
  11. Chest Pain
    1. Coronary Artery Disease
    2. Pulmonary Embolism
    3. Aortic Dissection
  12. Palpitations
    1. Possible Arrhythmia
  13. Incontinence of urine or stool
    1. Seizure Disorder
    2. Vasovagal Syncope (however, uncommon in Syncope)
  14. Severe Abdominal Pain or back pain
    1. Abdominal Aortic Aneurysm
    2. Aortic Dissection
  15. Pelvic Pain or Vaginal Bleeding
    1. Ectopic Pregnancy

XIV. Symptoms: Prodromal

XV. Exam

  1. Vital Signs
    1. Temperature
    2. Blood Pressure
    3. Orthostatic Blood Pressure (low yield)
      1. Frequently abnormal in healthy subjects and a majority of the elderly
      2. However, in elderly, Orthostatic Hypotension may alter disposition and management
      3. Evaluate patient for symptoms reproduced on standing (more important than measurements)
  2. General
    1. Pallor
      1. Orthostatic Hypotension due to Anemia
    2. Tongue bitten
      1. Seizure
    3. Ear Exam
    4. Dix-Hallpike Maneuver
  3. Cardiovascular examination
    1. Carotid Bruit (poor Test Sensitivity and Specificity)
    2. Heart Murmur (evaluate new murmurs associated with Syncope)
      1. Aortic Stenosis
      2. Hypertrophic Cardiomyopathy
    3. Asymmetric Pulses
      1. Aortic Dissection
      2. Aortic Coarctation
      3. Subclavian Steal Syndrome
      4. Takayasu Arteritis
    4. Carotid massage (rarely performed in the acute setting)
      1. Avoid in Cerebrovascular Disease or Carotid Bruit!
      2. Used in neurally mediated Syncope to diagnose Carotid Sinus Hypersensitivity
    5. Congestive Heart Failure findings
      1. Left-sided Heart Failure (Pulmonary Rales, S3 Gallop Rhythm)
      2. Right-sided Heart Failure (Jugular Venous Distention, Edema)
  4. Abdomen and Pelvis Exam
    1. Pulsatile mass and decreased femoral pulses (Abdominal Aortic Aneurysm)
    2. Pelvic Pain in a young woman (e.g. Ectopic Pregnancy)
    3. Rectal Exam (gastrointestinal Hemorrhage)
  5. Neurologic Exam
    1. Post-event Confusion (Seizure Disorder)
    2. Focal neurologic deficit
      1. Perform a careful Neurologic Exam to identify subtle deficits
  6. Red flags suggestive of ongoing active cardiovascular or Syncope-plus cause
    1. Diaphoresis
    2. Tachycardia
    3. Dyspnea
    4. Significant pain
  7. Evaluate for injury related to syncopal fall
    1. See Trauma Evaluation
    2. Exclude head or neck injury
    3. Exclude Extremity Injury

XVI. Differential Diagnosis: Serious Causes

  1. Arrhythmia
    1. May be misdiagnosed as Seizure
    2. Wolff-Parkinson-White Syndrome (WPW Syndrome)
    3. Brugada Syndrome
    4. Prolonged QTc >500 ms
    5. Ventricular Tachycardia
  2. Structural heart defects and vascular conditions
    1. Hypertrophic Cardiomyopathy (esp. young patients)
    2. Aortic Stenosis
    3. Acute Mitral Valve Regurgitation
      1. Typically from acute Myocardial Infarction with papillary Muscle rupture
    4. Prosthetic Heart Valve complication (e.g. Thromboembolism, valvular obstruction)
  3. Acute catastrophic disorders (Rule of 15s: Each condition has a 15% Incidence as syncopal presentation)
    1. Aortic Dissection
    2. Ruptured Abdominal Aortic Aneurysm
    3. Ruptured Ectopic Pregnancy
    4. Subarachnoid Hemorrhage
    5. Acute Coronary Syndrome
    6. Pulmonary Embolism
      1. Consider if Leg Edema, Tachypnea, Dyspnea, Tachycardia or VTE Risk factors
      2. One study found high Incidence of PE in elderly, ill patients admitted for first-time Syncope
        1. Prandoni (2016) N Engl J Med 375(16): 1524-31 +PMID:27797317 [PubMed]

XVII. Differential Diagnosis: Non-Traumatic Transient Loss of Consciousness causes

  1. Seizure Disorder (2%)
    1. Not associated with preceding Nausea or diaphoresis
    2. Seizure activity precedes a fall
    3. Postictal period
  2. Neurovascular and other neurologic syndromes
    1. Transient Ischemic Attacks: 1-7%
    2. Vertebrobasilar Insufficiency
    3. Subclavian Steal Syndrome
    4. Dizziness or Vertigo (no loss of consciousness)
    5. Drop Attacks (No loss of consciousness, no aura)
  3. Systemic causes
    1. Muscle Weakness
    2. Metabolic Disorders
  4. Mental health disorders
    1. Acute Intoxication
    2. Cataplexy
    3. Psychogenic pseudosyncope
  5. Images
    1. DizzinessDDx.png


  1. Approach
    1. Targeted blood testing based on history and exam
  2. Basic Chemistry Panel (Serum Electrolytes including Glucose) Indications
    1. Low yield in young patients (age <40 years old) without other risk factors
      1. Bedside Glucose alone may be sufficient in these patients
    2. Patients warranting chemistry panel
      1. Patients over age 40 years old
      2. Prolonged QTc (include Serum Magnesium, Serum Calcium, Serum Potassium)
      3. Gastrointestinal losses (Vomiting or Diarrhea)
      4. Diabetes Mellitus
      5. Chronic Kidney Disease
      6. Diuretic use
      7. Dietary restrictions
  3. Hemoglobin or Hematocrit Indications
    1. Blood loss (e.g. Menorrhagia, GI Bleed)
    2. Comorbidity (HIV, cancer, Renal Failure)
    3. Signs (pallor, weakness)
  4. Pregnancy Test (urine HCG) Indications
    1. Have low threshold to obtain in women of child bearing age (risk of Ectopic Pregnancy)
    2. Abdominal Pain
    3. Vaginal Bleeding
  5. Fecal Occult Blood Test Indications
    1. Anemia
    2. Associated gastrointestinal symptoms
  6. Troponin I
    1. Associated with a significantly worse outcome if elevated
    2. However Syncope is a rarely due to ACS or Myocardial Infarction (3% of cases)
      1. Arrhythmia is a more likely cause of Syncope
      2. Troponin Is positive in only 1.4% of Syncope patients
      3. Patients with Syncope due to ACS/MI should still appear ill at evaluation
    3. Indications
      1. Chest Pain, Shortness of Breath or other cardiopulmonary symptoms
      2. EKG with ischemic changes
    4. References
      1. Reed (2010) Emerg Med J 27(4): 272-6 +PMID:20385677 [PubMed]
  7. Brain Natriuretic Peptide (BNP)
    1. Non-specific and unlikely to affect management or disposition
    2. Earlier studies demonstrated an association with cardiac cause of Syncope
      1. Tanimoto (2004) Am J Cardiol 93:228-30 [PubMed]
  8. D Dimer Indications
    1. Significant venous Thromboembolism Risk Factors
    2. Shortness of Breath
    3. Pleuritic Chest Pain
    4. Tachypnea
    5. Hypoxia

XIX. Diagnostics

  1. Electrocardiogram (EKG)
    1. See Electrocardiogram in Syncope
    2. Obtain in all Syncope patients
      1. However, significant findings in only 5% overall, and 0-3% in those under age 40 years old
    3. Identify VT, Brugada Syndrome, WPW (short PR), Prolonged QTc >500, Hypertrophic Cardiomyopathy, ischemia
    4. May assist in distinguishing Seizure and Syncope
    5. EKG is low yield in syncopal patients under age 40 years old
      1. Sun (2008) Ann Emerg Med 51(3): 240-6 +PMID:17559972 [PubMed]
  2. Continuous cardiac monitoring (outpatient)
    1. Indications: Greatest benefit cases
      1. Cardiovascular disease
      2. Abnormal baseline EKG
      3. Syncopal event with associated cardiopulmonary symptoms
      4. Family History of Sudden Cardiac Death
    2. Devices
      1. Holter Monitor (24 to 48 hours of monitoring)
        1. Consider for daily symptoms
      2. External Event Monitor (4 to 8 weeks of monitoring)
        1. Consider for infrequent symptoms (weekly to monthly)
      3. Patch Monitor such as Zio Monitor (3 to 14 days of continuous monitoring via patch on upper left chest)
        1. Consider for weekly symptoms
      4. Implantable loop recorder (may remain implanted for up to 3 years)
        1. Consider for severe but infrequent symptoms
  3. Additional tests to consider
    1. Cardiac stress testing
      1. Indicated for Exertional Syncope or Angina
    2. Head-Up Tilt Test
      1. Indicated for suspected neurally mediated Syncope (distinguishing from Orthostatic Hypotension)
      2. Hypotension and Bradycardia indicate a positive provocative test

XX. Imaging: General

  1. Chest XRay
    1. Low yield test (positive in <0.6% of Syncope patients)
    2. Abnormal findings (e.g. Mediastinal Widening, Pneumonia, Pneumothorax) are unlikely without physical findings
    3. Obtain if Chest Pain, Dyspnea, increased Respiratory Rate or Hypoxia
  2. Echocardiogram
    1. Consider in suspected acute valvular cause of Syncope (especially if associated with new murmur)
    2. Consider if status-post prosthetic Valve Replacement (evaluate for significant valvular dysfunction, obstruction)
    3. Obtain for EKG consistent with Hypertrophic Cardiomyopathy (High voltage, deep narrow Q Waves)
    4. Evaluate for Hypertrophic Cardiomyopathy (HOCM), Aortic Stenosis, MI with acute Mitral Regurgitation
  3. Other imaging to consider
    1. CT chest with contrast (if Pulmonary Embolism is suspected)
    2. Imaging related to injuries sustained in a Syncope-related fall

XXI. Imaging: CT Head

  1. Efficacy: Low
    1. Head CT is very low yield in Syncope and not recommended unless indications below
    2. Goyal (2001) Intern Emerg Med 1(2):148-50 [PubMed]
    3. Grossman (2007) Intern Emerg Med 2(1):46-9 +PMID:17551685 [PubMed]
  2. Indications
    1. Trauma above the clavicles
    2. Persistent neurologic deficit
    3. Dizziness
    4. Sudden onset Headache (Thunderclap Headache of Subarachnoid Hemorrhage)
    5. Age over 65 years
    6. Warfarin use
    7. First Seizure

XXII. Evaluation: Reassuring findings suggestive of non-Cardiac Syncope (low risk Syncope, outpatient evaluation)

  1. Age <40 to 50 years old
  2. No cardiac history
  3. Chronic history of Syncope
  4. Normal evaluation findings (normal Vital Signs, normal Electrocardiogram, normal Troponin and BNP biomarkers)
  5. Findings most consistent with non-Cardiac Syncope (neuro-mediated Syncope, Orthostatic Syncope)
  6. Triggered by specific stimulus
    1. Noxious smell, sound, sight, pain or other specific trigger (e.g. Cough Syncope, micturation Syncope)
    2. Prolonged standing, crowded place, heat
    3. Orthostasis (occurs on standing from supine or seated position)
    4. Nausea or Vomiting
    5. Post-meal
    6. Rotation of head or tight collar, shaving
    7. Post-exertion

XXIII. Management: Hospitalization or Observation Indications (high risk Syncope)

  1. Abnormal San Francisco Syncope Rule (CHESS Criteria) or Canadian Syncope Risk Score
  2. Syncopal episode occurring during Exercise or exertion
  3. Family History of sudden death
  4. Severe Orthostatic Hypotension or low systolic Blood Pressure <90 mmHg
  5. Abnormal Vital Signs
  6. Severe Anemia (e.g. Hematocrit <30%, gastrointestinal Hemorrhage)
  7. Significant Electrolyte abnormalities
  8. Chest Pain or Shortness of Breath with episode
  9. Sudden onset of Palpitations prior to Syncope
  10. Advanced age
  11. Significant underlying cardiac disease
    1. Congestive Heart Failure
    2. Severe structural heart disease
    3. Coronary Artery Disease
    4. Cardiac Arrhythmia or suspected Arrhythmia
  12. Abnormal Electrocardiogram
    1. See Electrocardiogram in Syncope
    2. Prolonged QTc >500 ms (risk of Torsades de Pointes)
    3. Type 1 Brugada pattern and new onset Syncope
    4. Mobitz II AV Block or Third Degree Heart Block
    5. Persistent significant Bradycardia (Heart Rate <40 bpm not due to fitness)
  13. Syncope WITHOUT prodrome
    1. Arrhythmia is more likely if absent prodrome (e.g. Vision dimming, Light Headedness, Nausea, diaphoresis)
    2. However prodromal Dyspnea or Chest Pain also has been associated with Cardiac Syncope
  14. References
    1. Brignole (2001) Eur Heart 22:1256-306 [PubMed]

XXIV. Management: Outpatient

  1. Approach
    1. Emergency department discharge is indicated in the absence of high risk criteria (as above)
    2. Emergency department evaluation identifies 80% of causes
      1. Additional inpatient telemetry is unlikely to be diagnostic without high risk criteria
      2. Probst (2019) Ann Emerg Med 74(2): 260-9 [PubMed]
  2. Echocardiogram indications
    1. See imaging above
  3. Cardiac Event Monitoring (e.g. 7 to 14 day Zio patch monitor) indications
    1. Palpitations immediately prior to Syncope
    2. Prodrome absent prior to Syncope
  4. Tilt Table testing (and cardiology Consultation)
    1. Frequent Vasovagal Syncope episodes
  5. Exercise Stress Testing indications
    1. Not typically indicated in Syncope
    2. Consider in suspected coronary syndrome related history or findings (typically admit these cases)

XXV. Prognosis

  1. See San Francisco Syncope Rule (CHESS Criteria) or Canadian Syncope Risk Score
    1. Predicts short-term risk of serious outcome
  2. Short-term mortality is relatively low (0.7% at 10 days, 1.6% at 30 days)
  3. Long-term mortality is however, much higher (8-10% at 6-12 months, esp. Cardiac Syncope)
    1. Recurrence of Syncope is common (25% in 2 years)
    2. D'Ascenzo (2013) Int J Cardiol 167(1): 57-62 [PubMed]
    3. Soteriades (2002) N Engl J Med 347:878-85 [PubMed]

XXVI. References

  1. Joshi and Dermark (2016) Crit Dec Emerg Med 30(8):3-12
  2. Orman and Mattu in Herbert (2016) EM:Rap 16(3): 9-11
  3. Orman and Mattu in Herbert (2018) EM:Rap 18(6): 10-11
  4. Schauer et al. (2016) Crit Dec Emerg Med 30(9):13-9
  5. Bayard (2023) Am Fam Physician 108(5): 454-63 [PubMed]
  6. Brignole (2001) Eur Heart J 22:1256-306 [PubMed]
  7. Kapoor (2000) N Engl J Med 343:1856-62 [PubMed]
  8. Miller (2005) Am Fam Physician 72:1492-500 [PubMed]
  9. Runser (2017) Am Fam Physician 95(3): 303-12 [PubMed]
  10. Sheldon (2011) Can J Cardiol 27(2): 246-53 [PubMed]

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