See also Falls

Transient loss of consciousness due to transient global cerebral hypoperfusion characterised by rapid onset, short duration and spontaneous complete recovery

Syncope is one of several potential syndromes that cause a ‘transient loss of consciousness’.



  • What happened/happens?
    • Prior to the loss of consciousness
      • Is there any triggering event?  What was the patient doing?
        • Syncope following/during exertion is a red flag and requires urgent referral to a cardiologist, particularly if there is no known underlying cause
        • In a crowded and/or hot environment? Hydration/nutrition status (i.e. had they had breakfast?)?
        • Standing up quickly?  Change of head position?
      • Any prodromal features?
        • Pre-syncope
          • Dizzy, light-headed, sweaty, nauseous, visual disturbance (vision ‘closing-in’): all usually vasovagal cause
        • Palpitations
          • consider cardiac cause (see below)
        • Absence behaviour/abnormal movements
    • The loss of consciousness (usually witness history is more useful)
      • How long?  Any abnormal movements?
        • Jerking movements are not necessarily due to seizures- hypoxic jerks are commonly ‘mild’ and generalised 
          • make sure to get a good description if possible
        • See epilepsy for movements seen in seizure attacks
          • any tongue biting; any incontinence?
    • After the loss of consciousness
      • How quickly did the patient recover?  Were they themselves?  
      • Any residual symptoms e.g. palpitations, jerks, visual disturbance, weakness, etc
  • Any previous attacks?
  • Take a full medical history
    • Heart conditions/disease?
    • Drugs
  • Family history – cardiac and epilepsy?
  • Social History-
    • Alcohol intake (?XS)
    • Sleep pattern and diet could be relevant
    • (smoking)
    • Home circumstances- who found the patient?  who is at home with the patient?  do they have care packages?
    • Occupation/driving


  • Complete cardiorespiratory examination


  • FBC; U&Es
  • ECG- this is very important- all patients with a history of syncope should have an ECG test
    • Ambulatory ECG (e.g. Holter monitoring; event loop recorder etc) may be appropriate
  • Echocardiogram may be useful if there are signs on the ECG
  • Exercise testing/Adenosine triphosphate (stress) test
  • see below for tests for vasovagal syncope


  • Depends on the cause and type of syncope
  • The mainstay of management is education: avoidance of predisposing factors e.g. dehydration, stress, alcohol, extremely warm environments etc; anxiety management; reassurance
  • Drug treatments may be used – but are not recommended until an underlying cause is identified.  If no underlying cause is identified and the patient is having recurrent symptoms, consider a beta blocker, alpha blocker or SSRI (the effectiveness of these is not proven).
    • Pacemakers can be considered for patients with recurrent syncope caused by carotid sinus stimulation; minimal carotid sinus pressure induces ventricular asystole of > 3 s duration in the absence of any drug that depresses the sinus node or atrioventricular conduction
  • Tilt training is rarely offered as it has a low compliance and little proven efficacy

Types of syncope

There are three main classifications of syncope.  It is particularly helpful also to differentiate between cardiac and neuronally mediated syncope, as the former requires more intensive investigation and management, and can have a worse prognosis.

Reflex (neurally-mediated) syncope

  • Pathophysiology
    • A group of conditions in which neuronal reflexes of the cardiovascular system (normally important in controlling BP and circulation) become intermittently inappropriate, resulting in vasodilation and/or bradycardia in response to a trigger
    • Can either be classified based on the autonomic system that is dysfunctional or by the ‘trigger’
      • Autonomic classification
        • cardioinhibitory is used when over stimulation by parasympathetic system causes bradycardia +/- asystole
        • vasodepressor is used when under stimulation by the sympathetic system causes peripheral vasodilation and hypotension
      • Trigger
        • Vasovagal syncope (VVS)
          • ‘common faint’- mediated by emotion or orthostatic stress.  Usually preceded by a pre-syncopal phase (sweating, pallor, nausea)
        • Situational syncope (associated with a specific trigger- see below)
        • Carotid sinus hypersensitivity
          • an exaggerated response to carotid sinus baroreceptor stimulation
          • it can be diagnosed by carotid sinus massage (see below)
  • Presentation
    • May occur after fear, pain, distress or unpleasant physical sensation; with prolonged standing, often in crowded and hot places; after coughing, sneezing, eating (post-prandial syncope) or micturition; with head rotation, or with pressure on the carotid sinus (e.g. tight collars); following exertion
    • Often associated with nausea and/or vomiting
    • Patients may be entirely normal on examination- though findings on examination may provide evidence to exclude the diagnosis
  • Investigations
    • Carotid sinus massage
      • Should be done with ECG and BP monitoring and with full resuscitation equipment immediately available as there is a risk it can precipitate stroke or VF (i.e. should be done in a hospital)
        • Contraindicated in patients with MI; previous cerebrovascular event in the last 3 months; carotid artery occlusion (a bruit is a relative contraindication); history of VT/VF; previous reaction to massage
      • In the supine position, the carotid artery is massaged for 5-10secs at the anterior margin of the SCM muscle at the level of the cricothyroid cartilage.  If no response, the procedure is performed on the opposite side.  If there is a response, the procedure can be repeated after a dose of atropine (so to check if a vasodepressor response hasn’t been masked by a cardioinhibitory response).
        • A vasodepressor response is a drop in BP >50mmHg SBP
        • A cardioinhibitory response is asystole for >3 secs
    • Tilt-testing
      • It is only really used for confirming a diagnosis of reflex syncope in patients in whom the diagnosis has not been confirmed by initial evaluation (rare); differentiating between cardiac and reflex syncope; and in confirming syncope over epilepsy.
      • It can also aid in the diagnosis of delayed orthostatic hypotension
      • A response is classed in the same way as CSM but the diagnosis will be more certain if reproduction of syncope (t-LOC) is also found
      • Indicated in
        • recurrent syncope or a single syncopal episode accompanied by physical injury or motor vehicle crash or occurring in a high risk setting (for example, pilot, surgeon, commercial vehicle driver) and no evidence of structural cardiovascular disease; or presence of structural cardiovascular disease but other causes of syncope ruled out by diagnostic testing
        • Syncope induced by or associated with exercise
        • Further evaluation of patients in whom an apparent specific cause of syncope has been established (for example, asystole, high atrioventricular block) but susceptibility to neurocardiogenic syncope may affect treatment plan
      • Contraindicated in
        • Syncope with severe left ventricular outflow obstruction (for example, aortic stenosis)
        • Syncope in presence of severe mitral stenosis
        • Syncope in setting of known critical proximal coronary artery disease
        • Syncope in setting of known critical cerebrovascular disease
  • Management
    • Reassurance and education
      • avoidance of potential triggers
      • action at first signs of syncope (pre-syncope) e.g. lie down; squatting down
    • Active treatment is rarely required (only if very frequent/unpredictable/potentially dangerous attacks)
      • Tilt training
      • Counterpressure manoeuvres e.g. leg crossing
      • Indications for a cardiac pacemaker
        • If the patient has frequent cardioinhibitory carotid sinus hypersensitivity syncope, a pacemaker may be inserted

Orthostatic Hypotension

Cardiogenic Syncope

This can largely be split via distinct mechanisms:

  • Arrhythmias
    • Particularly bradycardic rhythms e.g. heart block, sick sinus syndrome
    • More rarely, tachycardic rhythms e.g. SVTs and VT can cause syncope (more frequently causes palpitations)
  • Valvular disease
    • Stenotic disease (particularly aortic stenosis) can cause syncope- commonly on exertion or after medications for BP/heart rate e.g. beta-blockers.
  • Myopathic disease
    • hypertrophic cardiomyopathy (e.g. seen in heart failure) can also reduce blood flow to the brain and cause syncope
  • Inherited syndromes
    • Prolonged QT and brugada’s syndrome
  • Acute coronary disease or cardiac failure 

One thought on “Syncope”

  1. Nice post. Syncope is a difficult problem to evaluate and manage. I would like to say that I have posted a clinical approach to syncope

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