Presyncope

Presyncope is the sensation of impending loss of consciousness, with lightheadedness, visual dimming and weakness, without actual loss of consciousness. It shares causes with syncope and warrants careful risk stratification.

• Causes: reflex (vasovagal, situational), orthostatic hypotension, cardiac arrhythmia, structural heart disease (aortic stenosis, hypertrophic cardiomyopathy), anaemia, hypoglycaemia, dehydration, medications, hyperventilation.
• Cardiac causes carry the highest risk of sudden death.

Gradual dimming or tunnelling of vision, sweating, pallor, nausea, ringing in ears, weakness, relieved by lying flat.

• Triggered by standing, heat, pain, venepuncture, prolonged standing, micturition, cough, or exertion.
• Palpitations or chest pain point to arrhythmia or ischaemia; exertional onset points to obstruction.
• Differential diagnosis: vestibular disease, anxiety, hypoglycaemia, anaemia, pulmonary embolism, seizure, hypotension from sepsis or haemorrhage, hyperventilation, medication effect.
• Complications: syncope with injury, falls, driving accidents, sudden cardiac death in structural or arrhythmic disease, anxiety and activity restriction.

History, orthostatic blood pressure and 12 lead ECG are the core assessment.

• Lying and standing blood pressure at 1 and 3 minutes; heart rate; cardiac auscultation.
• ECG for rhythm, QT, pre excitation, Brugada pattern, conduction block; glucose; haemoglobin; urea, electrolytes; pregnancy test.
• Echocardiography for murmur, abnormal ECG or heart failure; ambulatory ECG monitoring (24 hour to 14 day) for suspected arrhythmia; exercise testing for exertional symptoms; tilt testing for recurrent unexplained reflex episodes.

Treat the cause and prevent progression to syncope.

• Supportive: lie down or sit with head between knees at onset; leg crossing and hand grip counterpressure manoeuvres; avoid prolonged standing and heat; fluid 2 to 3 litres daily and salt 6 to 10 g daily if no hypertension or heart failure; avoid alcohol and abrupt standing.
• Pharmacological: stop or reduce offending antihypertensives, diuretics, alpha blockers and nitrates. Correct anaemia with iron or transfusion by cause. For orthostatic or reflex types unresponsive to measures: fludrocortisone 0.05 to 0.1 mg daily, or midodrine 2.5 to 10 mg three times daily during daytime (last dose 4 hours before bed). Beta blocker not effective for reflex presyncope in young adults.
• Procedures: pacemaker for documented bradyarrhythmia, catheter ablation for tachyarrhythmia, valve replacement for severe aortic stenosis, implantable defibrillator for high risk cardiomyopathy.
• Special groups: pregnancy, left lateral position and fluids; elderly, review medicines, treat carotid sinus hypersensitivity, falls prevention; athletes, cardiology review before return to sport.
• Red flags: exertional presyncope, chest pain, dyspnoea, abnormal ECG, family history of sudden death under 50 years, heart failure, murmur, recurrent episodes with injury, severe anaemia, occult bleeding.
• Follow-up: review at 2 to 4 weeks with results; advise on driving; repeat orthostatic readings after medicine changes.