Last Updated on by frcemuser

Causes of Syncope

  • Neurally – mediated reflex syncopal syndromes – Vasovagal (emotional reactions) or Valsalva (micturition, cough, straining etc)
  • Orthostatic – orthostatic drop of >20mm systolic blood pressure or >10 mm diastolic blood pressure volume depletion from dehydration or haemorrhage or to venodilatation caused by medications or Primary autonomic failure syndromes (eg as occurs in Parkinsons Disease), Secondary autonomic failure syndromes (e.g. diabetic neuropathy, amyloid neuropathy)
  • Cardiac –  arrhythmias, cardiac failure, ventricular dysfunction (eg. hypertrophic obstructive cardiomyopathy HOCM) and valvular heart disease
  • Neurological / Cerebrovascular – basilar artery migraine, vestibular dysfunction and vertebrobasilar ischaemia, Vascular steal syndromes
  • Psychiatric syncope-  anxiety, depression

Differential Diagnosis

  • Metabolic disorders, including hypoglycaemia (not true syncope as not spontaneously reversible), hypoxia, hyperventilation with hypocapnia
  • Epilepsy
  • Intoxications
  • Vertebro-basilar transient ischaemic attac

Clinical assessment


  1. Circumstances: what lead up to the episode?
  2. Duration: how long was the period of loss of consciousness?
  3. Associated symptoms: was there chest pain, breathlessness or palpitations? Was there a prodrome?
  4. Position: was the patient supine, sitting or standing?
  5. Activity: did the episode occur at rest; after a change in posture; during or after exercise; during or after urination, defecation, cough or swallowing?
  6. Predisposing factors: was this in a crowded or warm place; after prolonged standing; or after a meal. Were there precipitating events?
  7. Post recovery symptoms: was there nausea or vomiting? Was there incontinence or tongue biting? Was there a confusional state?

Other factors which are important to establish in the history:

  • A witness account is often critical in helping to determine a cause: was there cyanosis or pallor? Were there movements suggestive of a fit? If so did it occur before or after the collapase?
  • Relevant comorbid diseases: particularly previous cardiac disease, diabetes, Parkinsons disease, etc.
  • Relevant family history: is there a family history of sudden death (could indicate underlying arrhythmic disorder eg. Brugada syndrome)?
  • Relevant drug History: specifically ask about cardiovascular drugs (eg. beta blockers, ACE inhibitors, nitrates, calcium antagonists, digoxin, diuretics, antiarrythmics) and other drugs (eg. phenothiazines, insulin).



  • FBC (anaemia?)
  • UEC
  • glucose
  • blood gas (venous often sufficient)
  • Consider D-dimers if pulmonary embolism is suspected
  • ECG for causes of sudden collapse
  • HCG
  • Lying standing BP
  • Echocardiography

CT brain:

  • if suspected first seizure
  •  if secondary trauma sustained during the syncopal episode (“trauma above the clavicle”)
  • if suspected TIA or stroke
  • if neurological deficit or ongoing altered conscious state / confusion
  • if Age >65
  • if sudden onset headache
  • if patients on warfarin (coumadin)

Risk stratification tools

OESIL Score 

  • age over 65 years;
  • previous history of cardiovascular disease;
  • syncope without prodrome and
  • abnormal ECG

The score predicts 12 month mortality which rises from under 1% for patients with no risk factors to over 50% in patients with all 4 risk factors.

The San Francisco Rule 

  • History of congestive cardiac failure
  • Haematocrit < 30%
  • Abnormal ECG
  • Complaint of shortness of breath
  • Systolic Blood Pressure <90 mm Hg

The presence of any factor is considered sufficient for the patient to be high risk.

The EGSYS Score


Predictor Score
Palpitations preceding syncope 4
Syncope during effort 3
Heart disease/ abnormal ECG 3
Syncope while supine 2
Precipitating/ predisposing factors -1
Autonomic prodromes -1

This specifically identified cardiac syncope with a score of 3 or more being 99% sensitive and 65% specific for identifying cardiac syncope (positive and negative predictive values 33% and 99%).

Discharge criteria

Patients can usually be discharged if:

  • They do not have significant clinical risk factors, including:
    • abnormal ECG
    • CVS risk factors
    • Initial hypotension
    • Initial history of shortness of breath
    • Witnessed seizure activity or a history of seizures, especially when the event is unwitnessed
    • Observations and clinical findings are normal
    • Medications reviewed
    • Safe home environment (especially the elderly)


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