Syn; together, kopein; to cut (Greek) – referring to a block in blood supply from the body to the brain, most often due a drop in systemic blood pressure<span class="su-quote-cite">From the Greek</span>


Defined as:

  1. Temporary and transient
  2. A form of loss of consciousness (floppy body – loss of postural tone)
  3. Related to global cerebral hypoperfusion (in contrast, focal cerebral hypoperfusion occurs in TIAs for example)
  4. Rapid onset, short duration, spontaneous recovery, length of loss of consciousness is usually less than a minute
  • It is a symptom, not a disease. Therefore your assessment should focus on what caused the syncopal episode.
  • Also sometimes heard as ‘fainting’, ‘passing out’, ‘black-out’, ‘losing consciousness’. But these terms should not be interchangeably used with syncope because there are non-syncopal causes of loss of consciousness.
  • Pre-syncopal changes (prodrome) can occur depending on the cause: such as going pale, clammy, chest pain, or none in some cases of cardiac causes.
  • Be aware that “presyncope” is a feeling that a person may faint but is not associated with complete loss of postural tone or loss of consciousness.

Syncopal causes of loss of consciousness: (most common to less common)

Reflex Vasovagal (neurocardiogenic)Due to reflex bradycardia +/- peripheral vasodilationProvoked by emotion, pain, fear, stress. Normal investigations +/- postural drop, reduced HR, dilated pupils. Most common in young patients
CardiacReduction in CO (arrhythmias, outlet obstruction, AS, HOCM),+/- chest pain, palpitations, SOB, fast, slow or irregular pulse, ECG key +/- cardiac markers. Keep in mind the possibility of PE and aortic dissection. Most common in middle-aged patients. May need a cardiac monitor as can be high risk of further episodes.
OrthostaticSudden drop in BP from lying/sitting to standing (a drop defined as >or=20mmHg systolic or >or=10mmHg diastolic)Hypovolaemia will cause this due to dehydration or shock and responds usually to IV fluids. Alternatively, can be caused by drugs (e.g. anti-hypertensives) or autonomic neuropathy in Parkinson’s syndromes or diabetes mellitus. Most common in the elderly.
SituationAction relatedMicturition (elderly men at night), defecation, cough, effort (post-exercise syncope MUST be ix further to rule out cardiac structural abnormality)
Carotid sinus sensitivityHypersensitive baroreceptors causing excessive reflex bradycardiaSubtle movements e.g. when shaving or head-turning
CerebrovascularNon-cardiac structural causes of reduced cerebral perfusione.g. vertebrobasilar insufficiency / subclavian steal syndrome often presenting with unilateral arm symptoms or intermittent neurology (vertigo, visual loss and others)

Seizure or Syncope?

  • Both seizures and syncope can present similarly i.e. sudden loss of consciousness and +/- convulsions
  • Syncope is more likely to have “warning signs” and will usually be shorter than 1 minute (however people can be very poor at reporting the timing of such events due to their stress)
  • Both will need a full workup and if the LOC is longer than a minute, it is possibly a seizure
A thorough history is important
  • Remember as with falls history: before, during & after the event
  • Collateral history is key! A video is even better.
  • Precipitant (action induced?), warning symptoms (nausea, sweating, blurred vision)
  • Is the patient dehydrated? What did they have to eat or drink during the day?
  • Positioning – did the patient get up suddenly?
  • Speed of recovery
  • Of course, not forgetting past medical history, drug history (any medication changes?), social history, family history (all to rule out other causes)
  • A-E assessment especially listening for any cardiac murmurs/pulse
  • Make sure to conduct a neurological examination
  • May be unremarkable but important for thorough examination CVS/RS/GI/Neuro to rule out other worrying causes
  • Check blood glucose by bedside
  • Send off a full set of bloods incl. Hb and electrolytes to check for any underlying causes
  • If any concerns of trauma/fall examine hips/painful joints etc. as per your Post-Falls review (incl. neurological observations and CT if your patient is showing neurology deficits or has hit their head)
  • Full set of up to date observations including lying/standing BP (be careful if you suspect an orthostatic cause when checking BP)
  • Bloods to rule out other underlying causes of ‘blackouts’ such as anaemia, electrolyte imbalances, things which may cause arrhythmias and don’t forget glucose!
  • ECG – Always compare with previous and remember, a normal ECG does not rule out cardiac cause if the arrhythmia is intermittent! May need a 24-hour tape.
  • If QT is prolonged, identify any drugs which could cause this and discuss with your seniors
Concerning features
  • Underlying structural cardiac disease
  • Family history of sudden death
  • Abnormal ECG (particularly bradycardia or prolonged QRS or abnormal QT intervals)
  • Occurring at rest or on exercise or in concerning situations such as driving
  • Absence of warning features


  • Those with vasovagal or situational triggers can be educate to avoid these triggers. If symptoms do occur they can be taught at the first warning of potential collapse, to lie down with the legs bent or raised or sit down on the ground with their head tucked between their knees.
  • Orthostatic hypotension is again managed as above, with particular attention to dehydration or medications. If symptoms continue to be troubling or are persistent, compression stockings or medications (e.g. fludrocortisone) can be considered providing there are no contraindications
  • Cardiac or cerebrovascular syncope management will be as per the specialist team

Final Notes

  • Different types of syncope can co-exist.
  • A good thorough history will help you to rule out concerning causes.
  • Examinations and investigations can be unremarkable but important to rule out any other diseases or conditions. Your immediate investigations might not reveal a cause but be prepared to investigate further.
  • Discuss with seniors if any concerns or further investigations required.
  • As with a lot of things during F1/2, escalate at any point you feel concerned, better to be safe than sorry if concerned!

References & Further Reading

Dr Jessica Emerson (FY3)
Dr Mohmedshahid Patel (FY1)

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