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Home | Articles | Neurology | Transient Loss of Consciousness

Transient Loss of Consciousness

Last updated 13th June 2024

Causes vary from completely benign to life threatening. The commonest cause is probably syncope.

What is Syncope?

  1. Transient loss of consciousness and postural tone caused by abrupt decrease in cerebral perfusion with subsequent spontaneous recovery.

Pathophysiology of Syncope

  1. Consciousness is maintained by proper functioning of both cerebral hemispheres and the Reticular Activating System in the brain stem. This in turn depends on an adequate supply of oxygen and glucose. Syncope occurs when the supply of oxygen and glucose is interrupted.
  2. Note that carotid TIA and carotid territory strokes do not present with syncope because only one cerebral hemisphere is affected.


  1. Sixth commonest reason for hospital admission in adults >65 years
  2. Cause never determined in up to 50% of those who present to hospital
  3. Approximately 1/3 recur within three years.

Differential Diagnosis TLOC

This includes the causes of syncope and other causes of TLOC such as seizures. A useful approach is to ask:

  1. Is it a fit?
  2. Is it a faint (vasovagal or neurocardiogenic syncope)?
  3. Could it be cardiac (see below)?
  4. Could a drug have been responsible?
  5. Were they hypo?
  6. Do they have a GI bleed.
  7. Were they hyperventilating?

Ten Cardiovascular Causes

  1. Bradycardias especially intermittent complete heart block (Stokes-Adams attack), also sick sinus syndrome.
  2. Tachycardias especially paroxysmal VT but also occasionally AF and SVT.
  3. Obstructive lesions especially aortic stenosis but also hypertrophic cardiomyopathy.
  4. Orthostatic hypotension.
  5. Cardiovascular drugs eg anti-arrhythmics, antihypertensives.
  6. Acute coronary syndrome.
  7. Pulmonary embolus.
  8. Aortic dissection.
  9. Pericardial tamponade.
  10. Carotid sinus syndrome.

10 Questions to Ask Patient with TLOC

  1. Did They Lose Consciousness?
    1. Bear in mind that the elderly may have amnesia for LOC
    2. Ask if patient remembers hitting the floor.
  2. What Were They Doing at The Time?
    1. Pain, fear, anxiety, recent meal suggests vagal.
    2. Prolonged coughing or micturition suggests vagal.
    3. Supine indicates cardiac cause or seizure
    4. From supine to standing could be vagal or postural hypotension.
    5. During exertion raises possibility of aortic stenosis or HCM.
    6. If tight collar or shaving then consider carotid sinus syncope.
  3. What Symptoms Do They Recall Before Passing Out?
    1. Progressive light headedness, weakness and tunnelled vision suggests vagal or postural hypotension.
    2. No symptoms at all suggests cardiac cause or seizure.
  4. What Symptoms Do They Recall on Recovery?
    1. Tongue biting and confusion > 5 minutes favours seizure.
    2. Physical weakness favours vagal.
  5. Were There Any Witnesses?
    1. A witness account of the ONSET of attack is essential. There MUST be some evidence in notes that this question has been asked AND that an attempt has been made to contact. Use the telephone! Ask about: colour, whether floppy or rigid, clonic movements bearing in mind that patients who faint may have clonic movements for a few seconds, especially if propped up,duration of LOC and mental state on recovery.
  6. Has This Ever Happened Before?
    1. If so what was the result of cardiac cause or seizure work up.
  7. What Drugs Were They Taking?
    1. Antihypertensives.
    2. Anti arrhythmics.
    3. Anti anginal e.g. GTN syncope.
    4. Anti Parkinsonian.
    5. Anti diabetic drugs.
  8. What Illnesses Have They Had in The Past?
    1. LOC in diabetic is hypoglycaemia until proven otherwise.
    2. Cardiac disease makes a cardiac cause more likely.
    3. Recent surgery suggests PE.
  9. Is There a Family History of Sudden Death?
    1. Hypertrophic cardiomyopathy.
    2. Brugada syndrome – clue is coved ST elevation in V1/V2 with RBB
  10. Specifically Did They Experience?
    1. Chest pain – e.g. ACS, aortic dissection, PE.
    2. Breathlessness e.g. ACS in elderly, PE, tamponade.
    3. Palpitations – indicating dysrhythmia (though most patients with dysrhythmic LOC will not have palpitations).
    4. Headache before LOC e.g. subarachnoid.
    5. Leg pain or swelling suggests PE.
    6. Abdominal/low back pain e.g. ectopic, AAA.

Essential Examination (of Patient Who Has Recovered Fully)

  1. Heart rate.
  2. Blood pressure lying and standing.
  3. Listen for murmur of AS and HCM (louder with Valsalva).
  4. PR if anaemic.
  5. Evidence of tongue biting.

Essential Investigations

  1. Routine bloods – FBC, urea and electrolytes, glucose.
  2. ECG to exclude AV block, LVH, ACS, WPW, prolonged QT
  3. Overnight telemetry.
  4. Carotid sinus massage in selected cases.

Five Ps That Suggest Simple Faint

  1. Posture – prolonged standing or similar episodes that have been prevented by lying down
  2. Precipitating factors – eg pain or medical procedure
  3. Prodrome – such as sweating or feeling warm
  4. Pallor – though this can also occur with cardiac syncope
  5. Physical weakness – but not confusion

Tests That Do Not Usually Help

  1. 24 hour ECG if nothing picked up on telemetry.
  2. CT head scan unless LOC associated with severe headache.
  3. Echo unless has aortic murmur, ECG, LVH or recurrent syncope.
  4. Carotid doppler – carotid TIA causes focal neurological deficit without LOC whereas syncope causes LOC without focal neurological deficit.

When is it Safe Not to Admit?

  1. When vasovagal syncope much more likely than cardiac syncope:
    1. Patient less than 45 – 50 years.
    2. Clear precipitating event.
    3. No known or suspected heart disease.
    4. Normal ECG.

Advice on Driving

  1. No restriction on private drivers (Group 1) after first unexplained syncope unless absence of prodrome or syncope occurred while driving or severe structural heart disease
  2. Professional drivers (Group 2) should contact DVLA
  3. See Links section below for more advice.