🎯 Pathology

• transient loss of consciousness due to global cerebral hypoperfusion followed by spontaneous recovery

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💡 Causes

• cardiac disorders

  • cardiac arrhythmias (e.g. tachyarrythmias and bradyarrythmias)

  • valvular heart diseases (e.g. aortic stenosis)

  • structural heart diseases (e.g. hypertrophic obstructive cardiomyopathy, atrial myxoma)

• disorders of vascular tone

  • vasovagal syncope

  • carotid sinus syncope

  • vertebrobasilar insufficiency

  • orthostatic hypotension

  • situational syncope

• conditions that mimic syncope

  • seizures

  • hypoglycaemia

  • factitious blackouts (e.g. Munchausen’s syndrome, pseudoseizures)

  • cataplexy

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🕵️‍♂️ Assessment

• full thorough history

  • double-check if the patient is on medications that promote orthostatic hypotension

• full cardiovascular and neurological examination

• to rule out cardiovascular disorders

  • ECG +/- 24-hour Holter monitor (to check for arrhythmias)

  • echocardiogram (to rule out structural and valvular causes)

• to rule out postural hypotension

  • lying and standing BP

    • postural hypotension is positive if the blood pressure drops more than >20/10 mmHg

  • tilt table test

• neurological disorders

  • CT/MRI head

  • EEG

  • CT angiogram for vertebrobasilar insufficiency

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🧩 Differential diagnosis of syncope

 

Vasovagal syncope

• common faint, accounting for more than 50% of cases of syncope

• triggered by emotion and stress

• preceded by prodromal symptoms such as blurred vision, dizziness, nausea and sweating

• unlike seizures, there is no post-ictal phase, although rarely, patients may jerk their limbs

 

Orthostatic hypotension

• “a brief episode of dizziness from lying down to standing”

• the blood pressure drops more than >20/10 mmHg with standing up

• potential causes:

  • impaired vascular tone due to autonomic failure

    • primary causes: Parkinson’s disease

    • secondary causes: diabetic mellitus (diabetic neuropathy)

  • loss of blood volume

    • e.g. haemorrhage, diarrhoea

  • medications

    • e.g. diuretics, vasodilators

 

Carotid sinus syndrome

• the baroreceptors in the carotid sinus are hypersensitive, triggering the activation of the parasympathetic nervous system leading to bradycardia and brief loss of consciousness

  • triggered by activities such as shaving, tying a tie, neck turning

 

Vertebrobasilar insufficiency

• decreased flow of blood to the posterior circulation

• the patient passes out with neck extension

• no prodromal period

• best test: CT angiogram

 

Situational syncope

• activities that increase vagal tone (parasympathetic activity) lead to syncope

  • possible triggers: coughing, micturition, defaecation

 

Seizures

• stages of a seizure:

  • prodromal phase (e.g. aura) —> loss of consciousness —> tonic phase (limbs are stiff) —> clonic phase (jerking of the limbs) —> post-ictal phase

• tongue biting and urinary/faecal incontinence can occur

• the post-ictal phase can last up to 30 minutes, where the patient may experience amnesia, drowsiness and muscle weakness (Todd’s palsy)

 

Hypoglycaemia

• neuroglycopenic symptoms occur when the concentration of blood glucose in the blood is less than 2.8 mmol/L causing symptoms such as:

  • loss of consciousness

  • seizures

  • coma

 

Factitious blackouts

• the patient is faking a blackout

 

Cataplexy

• loss of muscle tone following intense emotional stimuli

• individuals may close their eyes

• affects patients with narcolepsy

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🧲 High-yield tips

• drugs that precipitate orthostatic hypotension

  • ​diuretics

  • ACE-inhibitors

  • nitrates

  • anti-cholinergics

  • anti-depressants

  • L-Dopa

  • nitrates