Syncope: Causes and Diagnosis

• Syncope is a transient loss of consciousness due to global cerebral hypoperfusion, with rapid onset, short duration, and spontaneous recovery.
• Diagnostic criteria include loss of consciousness with loss of postural tone, transient nature, and cause of low blood pressure.
• Key features include rapid onset, short duration (≤20 seconds), and complete recovery.

Syncope vs Seizure

• Syncope often has triggers like emotion or pain, a prodrome of dizziness or nausea, brief unconsciousness, and no post-ictal state.

Causes of Syncope

• SNAP mnemonic helps classify syncope: Structural, Neurally mediated, Arrhythmic, and Postural.

Neurally Mediated Syncope

• Common due to an inappropriate autonomic reflex (e.g., vasovagal, situational, carotid sinus hypersensitivity).
• Also known as reflex syncope

Vasovagal Syncope

• Most common type, often in young individuals, following emotional response or prolonged standing.

Situational Syncope

• Occurs consistently after a specific trigger like post-micturition, cough, swallow, defecation, prandial, or exercise.
• Post-exercise syncope requires investigation to rule out structural cardiac cause.

Carotid Sinus Hypersensitivity

• Syncope after mechanical manipulation of the carotid sinus.

Neurally Mediated Syncope: History

• Inquire about precipitants, warning symptoms (nausea, sweating, feeling faint), and position (usually standing for vasovagal).

Neurally Mediated Syncope: Investigations

• Includes lying and standing blood pressure, tilt table testing, and carotid sinus massage (with specific protocol/contraindications).

Postural Syncope

• Caused by orthostatic hypotension; common causes include drugs, hypovolaemia, autonomic failure.
• Syncope is dependent on standing up and results from insufficiency of the baroreceptor response.

Orthostatic Hypotension: Causes

• Autonomic nervous failure secondary to drugs (antihypertensives, diuretics, antidepressants, alcohol).
• Hypovolaemia: may have a sinister underlying cause such as a gastrointestinal bleed.
• Primary autonomic nervous failure: usually present to some degree in the spectrum of disorders which includes Parkinson’s disease, Lewy body dementia and multi-system atrophy.
• Secondary autonomic nervous failure: occurs secondary to other conditions such as diabetes, uraemia and spinal cord lesions

Postural Syncope: History

• Includes position (association with standing), prodrome (may be prolonged), drug history, causes for hypovolaemia, and past medical history (diabetes).

Postural Syncope: Investigations

• Includes lying and standing blood pressure and tilt table testing.

Arrhythmic Syncope

• Caused by bradyarrhythmias (sick sinus syndrome, AV block) or tachyarrhythmias (VT, long QT syndrome); check for family history.
• Bradyarrhythmias are more likely to cause syncope than tachyarrhythmias.
• Evaluate family history of sudden death.

Bradyarrhythmias

• Can include sick sinus syndrome, second-degree atrioventricular block or third-degree atrioventricular block.
• Reduction in blood pressure during long pause (>3 secs) between impulse conduction failure and ectopic escape mechanism causes syncope.
• Pacemaker dysfunction should be considered as a cause of syncope if the patient already has a pacemaker.

Tachyarrhythmias

• Ventricular tachycardia (VT) is much more likely to cause syncope than supraventricular tachyarrhythmias.
• Torsades de pointes, a type of VT, can occur due to long QT syndrome, which can be caused by genetic mutations or medications.

Structural Syncope

• Mechanical obstruction in the heart (e.g., aortic stenosis, hypertrophic cardiomyopathy), usually during exertion.
• Compensation during exertion does not happen if obstruction to outflow and exertional syncope occurs due to blood pressure reduction during exercise.

Structural Syncope: Causes

• Can include valvular disease, cardiac masses, cardiomyopathy, pericardial disease, pulmonary embolism, or aortic dissection.

Arrhythmic and Structural Syncope: History

• Includes palpitations, cardiac symptoms, no prodromal warning, onset when sitting/lying/exercising, previous heart disease, drug history, family history of sudden cardiac death.

Arrhythmic and Structural Syncope: Investigations

• Includes resting 12-lead ECG, ECG monitoring (ambulatory or loop recorders), and echocardiography.

Syncope History: Mnemonics

• The five Ps: Precipitant, Prodrome, Position, Palpitations and Post-event phenomena.
• The five Cs: Colour, Convulsions, Continence, Cardiac problems and Cardiac death family history.