Vasovagal Syncope

Vasovagal (reflex or neurally mediated) syncope is a transient loss of consciousness caused by an abnormal autonomic reflex that produces sudden vasodilatation and relative or absolute bradycardia, leading to cerebral hypoperfusion. It is the commonest cause of fainting at all ages, with a first peak in adolescence and a second in older age, and is generally benign.

• Triggers: prolonged standing, heat, crowded places, emotional distress, pain, venepuncture or the sight of blood, fasting, dehydration, alcohol, illness, and exertion followed by sudden stopping.
• Situational variants: micturition, defecation, cough, swallow, and carotid sinus hypersensitivity (older men, neck pressure).
• Prognosis is good unless there is structural heart disease, in which case the syncope may be arrhythmic and carries risk of death.

• Prodrome lasting seconds to minutes: light headedness, nausea, warmth, sweating, pallor, blurred or tunnel vision, tinnitus, yawning, abdominal discomfort.
• Loss of consciousness for less than a minute, with brief myoclonic jerks possible, rapid recovery once supine, and no prolonged postictal confusion.
• Residual fatigue, nausea and pallor for minutes to hours.
• Occurs upright, relieved by lying flat, and often follows a recognisable trigger.
• Features pointing away from vasovagal cause (red flags): syncope during exercise or lying supine, chest pain, palpitations preceding the event, family history of sudden death under 40, known heart disease, heart failure signs, murmur, abnormal ECG, no prodrome, injury, age over 65 with new onset.
• Seizure features (tongue biting laterally, prolonged confusion, incontinence with prolonged jerking) suggest epilepsy.

• Diagnosis is clinical: a typical trigger, a prodrome and rapid recovery, with a normal examination and normal ECG.
• Examination: lying and standing blood pressure, pulse, cardiac auscultation, neurological examination.
• 12-lead ECG in all patients with syncope, looking for long or short QT interval, pre-excitation, Brugada pattern, conduction disease, ventricular hypertrophy, left bundle branch block, ischaemia, arrhythmogenic cardiomyopathy changes.
• Capillary glucose, haemoglobin and, when indicated, electrolytes and pregnancy test.
• Echocardiography and ambulatory ECG monitoring if features suggest heart disease or if the history is atypical.
• Tilt table testing is reserved for recurrent unexplained syncope when the diagnosis is uncertain, after specialist review.
• Carotid sinus massage (under monitoring) in patients older than 40 with unexplained syncope, after excluding carotid bruit and recent stroke.
• Differentials: orthostatic hypotension, arrhythmia, structural heart disease, seizure, hypoglycaemia, anxiety or panic, cataplexy, psychogenic non-epileptic events.

Immediate

• Lay the patient flat and raise the legs. Loosen clothing. Check airway, breathing, pulse and glucose. Reassure.
• Do not sit the patient up too early; allow 10 to 15 minutes of recovery lying before slow rise.

Education and non-pharmacological prevention (core treatment)

• Identify triggers and avoid them where possible, and recognise the prodrome.
• At the first warning, lie down, or sit with the head between the knees, or perform counter pressure manoeuvres: leg crossing with muscle tensing, handgrip squeezing for 2 minutes, arm tensing.
• Maintain fluid intake of 2 to 3 litres daily, with liberal salt (6 to 10 g daily) if blood pressure is normal or low and there is no heart failure or renal disease. A 500 mL water bolus can abort or reduce episodes.
• Avoid excessive alcohol, prolonged standing in heat, skipping meals.
• Tilt training (standing against a wall for progressively longer, building to 30 to 40 minutes daily) may help motivated patients.
• Review and reduce blood pressure medicines in those on antihypertensive therapy and with low or normal pressure.
• Driving: advise against driving until the cause is established and episodes are controlled, particularly if syncope occurred without warning, and advise professional drivers to seek specific licensing advice.

Pharmacological (only for frequent, injurious or refractory episodes; specialist initiated)

• Midodrine 2.5 to 10 mg orally three times daily (last dose at least 4 hours before bedtime) may reduce recurrence in younger patients with low blood pressure; monitor for supine hypertension and urinary retention.
• Fludrocortisone 0.1 mg orally once daily, up to 0.2 mg, with potassium and blood pressure monitoring.
• Beta blockers are not recommended routinely and should not be used for prevention in young patients.
• Pacing may be considered by cardiology in carefully selected older patients with documented cardio inhibitory (asystolic) syncope.

Special groups

• Children and adolescents: fluids, salt, counter manoeuvres, exclude cardiac disease with ECG; reassure.
• Pregnancy: avoid prolonged standing and lying flat on back, left lateral position; midodrine and fludrocortisone avoided unless advised by a specialist.
• Older adults: investigate more thoroughly, check for orthostatic hypotension, review drugs, consider carotid sinus hypersensitivity.

Follow up and referral

• Urgent cardiology referral for exertional syncope, abnormal ECG, structural heart disease, family history of sudden death, syncope without prodrome, or injury from syncope.
• Review at 4 to 6 weeks and again if recurrent.