SN5 SHORT NOTE 5M

Write a short note on syncope.

General Medicine · Final Professional

Definition

Syncope is a transient loss of consciousness due to global cerebral hypoperfusion, characterised by rapid onset, short duration and spontaneous complete recovery. The definition excludes other causes of transient loss of consciousness — seizure, hypoglycaemia, intoxication and psychogenic attacks — which is why the mechanism is part of the definition.

Classification and Causes

Type	Mechanism	Examples
Reflex (neurally mediated) — commonest	Inappropriate autonomic reflex causing vasodilatation and/or bradycardia	Vasovagal (emotion, pain, prolonged standing, heat, venepuncture); situational (micturition, defecation, cough, swallow); carotid sinus hypersensitivity (tight collar, head turning — in the elderly)
Orthostatic hypotension	Failure to maintain blood pressure on standing (fall ≥ 20 mmHg systolic or ≥ 10 mmHg diastolic within 3 minutes)	Drugs (antihypertensives, diuretics, nitrates, alpha-blockers, antidepressants), volume depletion, autonomic failure (diabetes, Parkinson's disease, amyloidosis), adrenal insufficiency
Cardiac — the dangerous group	Arrhythmia	Bradyarrhythmia — sick sinus syndrome, complete heart block; tachyarrhythmia — VT, SVT, long QT syndrome, Brugada syndrome
Structural	Aortic stenosis, hypertrophic obstructive cardiomyopathy, massive pulmonary embolism, cardiac tamponade, atrial myxoma, aortic dissection

Clinical Distinction — the Critical Task

The essential job is to identify cardiac syncope, which carries a substantially increased risk of sudden death, and separate it from benign reflex syncope.

Feature	Reflex (vasovagal)	Cardiac
Trigger	Emotion, pain, standing, heat, crowded room	Exertion, or none; may occur supine
Prodrome	Nausea, sweating, pallor, greying of vision, warmth	Absent or very brief — "sudden collapse"
Posture	Almost always upright	Any, including lying down
Palpitations	Uncommon	Common before the event
Recovery	Rapid but with lingering nausea and fatigue	Rapid and complete
Age and history	Young, recurrent since adolescence	Older; known heart disease; family history of sudden death
Injury	Uncommon	More common

Red flags mandating urgent cardiac evaluation and usually admission: syncope during exertion or while supine, associated chest pain or palpitations, abnormal ECG, known structural heart disease or heart failure, family history of sudden cardiac death under 40, and syncope causing significant injury.

CLINICAL PEARL

Syncope on exertion is aortic stenosis or hypertrophic obstructive cardiomyopathy until proved otherwise, and both can cause sudden death. Examine specifically for an ejection systolic murmur, slow-rising pulse and displaced apex, and obtain an urgent echocardiogram. "Fainted while playing" is never a benign history in a young person.

Differentiation from Seizure

Reflex syncope may be accompanied by a few brief myoclonic jerks (convulsive syncope) as cerebral perfusion falls, and this is frequently misdiagnosed as epilepsy. Distinguishing features favouring syncope are the upright posture, autonomic prodrome, brief duration, absence of lateral tongue biting, and rapid complete recovery without prolonged confusion.

Investigations

History from the patient AND an eyewitness — the single most valuable investigation.
Full examination including lying and standing blood pressure, cardiac auscultation, and neurological examination.
12-lead ECG in every patient — looking for conduction disease, long or short QT, Brugada pattern, delta wave (WPW), pathological Q waves, and left ventricular hypertrophy.
Bloods: haemoglobin (anaemia and occult bleeding), glucose, electrolytes; pregnancy test where relevant.
Echocardiography where structural disease is suspected or the ECG is abnormal.
Ambulatory rhythm monitoring — Holter, external loop recorder, or implantable loop recorder for infrequent unexplained episodes with suspected arrhythmia.
Tilt-table testing for recurrent unexplained reflex syncope; carotid sinus massage in the elderly (avoid with carotid bruit or recent stroke).
Exercise testing for exertional syncope; electrophysiological study in selected cases.
EEG and neuroimaging are NOT indicated in typical syncope — they are over-ordered and low-yield unless the history suggests seizure or there are focal neurological signs.

Management

Reflex syncope:

Reassurance and education — explain the mechanism and its benign prognosis; identify and avoid triggers.
Recognise the prodrome and act: lie down and elevate the legs immediately.
Physical counter-pressure manoeuvres — leg crossing with tensing, handgrip, arm tensing — abort many attacks.
Adequate salt and fluid intake; avoid prolonged standing, heat and dehydration; review and reduce hypotensive drugs.
Midodrine or fludrocortisone in selected refractory cases; pacing only for documented severe cardioinhibitory syncope.

Orthostatic hypotension: withdraw or reduce culprit drugs (the most effective single measure), increase salt and fluid, compression stockings and abdominal binders, sleep with the head of the bed elevated, rise slowly in stages, and use midodrine or fludrocortisone if measures fail.

Cardiac syncope: treat the underlying cause — permanent pacemaker for bradyarrhythmia and heart block, antiarrhythmics or ICD for ventricular arrhythmia and inherited channelopathies, valve replacement for aortic stenosis, and management of hypertrophic cardiomyopathy. Advise on driving restrictions until the cause is treated.

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