Syncope (vasovagal, orthostatic hypotension, cardiac) !

A brief faint from a short drop in blood flow to the brain, with full, quick recovery. Most are harmless; some warn of heart disease.

Updated 2026-11-01

Structures involved

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In the clinical exam

Orthostatic vital signs

Why it happens

What it is

Syncope is a transient loss of consciousness and postural tone caused by global cerebral hypoperfusion, with rapid onset, short duration and spontaneous, complete recovery. It is grouped as reflex (neurally mediated, including vasovagal), orthostatic hypotension, and cardiac (arrhythmic or structural). Orthostatic hypotension, a sustained fall in blood pressure on standing, is also a leading cause of dizziness and falls in older adults.

Who gets it

One of the most common reasons for emergency visits worldwide; a large share of people faint at least once in life. Vasovagal syncope peaks in adolescents and young adults, while orthostatic and cardiac causes rise steeply with age. In Colombia and Latin America, Chagas cardiomyopathy with conduction block or ventricular arrhythmia is an important cardiac cause in people from endemic rural areas.

Causes

Reflex (vasovagal): triggered by pain, fear, the sight of blood, prolonged standing or heat; situational forms with coughing, micturition, defecation or swallowing; carotid sinus hypersensitivity in older men
Orthostatic hypotension: volume depletion (dehydration, bleeding, diarrhoea), drugs (antihypertensives, diuretics, alpha-blockers, nitrates, antidepressants, antipsychotics), autonomic failure (diabetes, Parkinson disease, multiple system atrophy, pure autonomic failure), alcohol and prolonged bed rest
Cardiac arrhythmic: sinus node disease, high-degree AV block, ventricular tachycardia, inherited channelopathies (long QT, Brugada), pre-excitation, pacemaker malfunction
Cardiac structural: aortic stenosis, hypertrophic obstructive cardiomyopathy, massive pulmonary embolism, pulmonary hypertension, tamponade, atrial myxoma, aortic dissection

Risk factors

Older age, multiple drugs (especially antihypertensives and diuretics) and dehydration
Known structural heart disease, heart failure or previous myocardial infarction
Diabetes and neurodegenerative disease (autonomic neuropathy)
Family history of sudden death at a young age
Prolonged standing, heat, fasting and alcohol (reflex syncope)

Pathophysiology

Consciousness is lost when cerebral blood flow falls abruptly for several seconds. Blood pressure equals cardiac output times peripheral resistance, so syncope arises when either falls. In vasovagal syncope a trigger causes vagally mediated bradycardia (cardioinhibitory) and withdrawal of sympathetic tone with vasodilation (vasodepressor). In orthostatic hypotension, about half a litre of blood pools in the legs and abdomen on standing and the baroreflex fails to restore pressure because of low volume, drugs or autonomic failure. In cardiac syncope a very slow or very fast rhythm, or a fixed obstruction to outflow, prevents cardiac output from rising.

Classification

Reflex (neurally mediated): vasovagal, situational, carotid sinus syncope
Orthostatic hypotension: classic (fall of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing), initial, delayed; drug-induced, volume depletion, neurogenic
Cardiac: arrhythmic (brady- or tachyarrhythmia) and structural (outflow obstruction, pulmonary embolism, tamponade)

Symptoms and signs

Prodrome in reflex syncope: lightheadedness, warmth, sweating, nausea, pallor, blurred or tunnel vision
Brief loss of consciousness, usually under a minute, with a fall and limp body; a few myoclonic jerks may occur
Rapid recovery with clear orientation, often with fatigue afterwards
Orthostatic hypotension: dizziness, blurred vision or weakness on standing up, after meals or in the morning, sometimes neck and shoulder ache («coat-hanger» pain)
Cardiac syncope: little or no warning, palpitations just before, or fainting during exertion or when lying down

Diagnosis

Clinical: A careful history from the patient and witnesses is the key step: posture, trigger, prodrome, duration, recovery and drugs. Orthostatic vital signs (lying, then at 1 and 3 minutes standing) confirm orthostatic hypotension. Seizure is suggested by tongue biting on the side, head turning, prolonged confusion afterwards; syncope by brief loss with quick recovery.
Tests: A 12-lead ECG in every patient. Glucose, haemoglobin and electrolytes when suggested; pregnancy test in women of childbearing age; troponin and D-dimer only when ischaemia or embolism is suspected. Ambulatory ECG monitoring (Holter, event recorder or implantable loop recorder) for recurrent unexplained episodes; tilt-table test for suspected reflex syncope or delayed orthostatic hypotension; carotid sinus massage in older adults under monitoring; exercise testing for exertional syncope.
Imaging: Echocardiography when structural heart disease is suspected (murmur, heart failure, abnormal tracing). Brain imaging is not routine and is reserved for focal neurological signs or head injury.

Differential diagnosis

Epileptic seizure
Hypoglycaemia
Transient ischaemic attack or vertebrobasilar ischaemia (rarely causes loss of consciousness)
Psychogenic pseudosyncope
Mechanical fall without loss of consciousness
Intoxication (alcohol, drugs)

Goal of treatment

Identify high-risk cardiac causes quickly, prevent recurrence and injury, and treat the specific cause (stop or adjust offending drugs, correct volume, pace or ablate arrhythmias, relieve obstruction).

Treatment

Acute: During an episode: lay the patient flat and raise the legs, protect the airway, check pulse and glucose, and treat any injury; patients with high-risk features are admitted for monitoring.
Lifestyle: Reflex syncope: education about triggers and early warning symptoms, physical counter-pressure manoeuvres (leg crossing, hand gripping, squatting), adequate fluid and salt intake unless contraindicated.
Lifestyle: Orthostatic hypotension: review and withdraw or reduce culprit drugs, rise slowly in stages, sit on the bed edge before standing, raise the head of the bed, compression stockings or abdominal binder, smaller meals and limited alcohol.
Medical: Selected refractory orthostatic hypotension or reflex syncope: volume-expanding mineralocorticoid (fludrocortisone) or alpha-agonist (midodrine), with monitoring for supine hypertension.
Procedure: Cardiac syncope: permanent pacemaker for symptomatic bradycardia or AV block, implantable cardioverter-defibrillator or catheter ablation for ventricular arrhythmias, and valve replacement for severe aortic stenosis.
Follow-up: Nursing: orthostatic vital signs, fall-risk assessment and precautions (call bell, assisted mobilisation, non-slip footwear), intake and output, and cardiac monitoring when a cardiac cause is suspected.

Complications

Injury from falls (fractures, head trauma), especially in older adults
Sudden cardiac death in untreated cardiac syncope
Fear of falling, loss of independence and reduced quality of life
Accidents while driving or operating machinery

Prognosis

Reflex syncope has an excellent prognosis though episodes may recur. Orthostatic hypotension in older adults is linked to falls, cognitive decline and higher mortality, largely through its causes. Cardiac syncope carries a significant risk of sudden death unless the cause is treated.

Prevention

Recognising and avoiding personal triggers and acting at the first warning symptom
Regular medication review in older adults, especially antihypertensives, diuretics and psychotropics
Staying well hydrated, mainly in hot weather and during illness
Treating the underlying heart disease and screening relatives in inherited arrhythmia syndromes

Test yourself

Think of the answer, then tap the question to see it.

How is classic orthostatic hypotension defined?

A fall in systolic pressure of at least 20 mmHg or diastolic of at least 10 mmHg within 3 minutes of standing.

Which test should every patient with syncope have?

A 12-lead ECG.

Which features suggest cardiac rather than reflex syncope?

Syncope during exertion or supine, palpitations or no warning, known structural heart disease, abnormal ECG and a family history of sudden death.

Which valvular lesion classically causes exertional syncope?

Severe aortic stenosis (with angina and heart failure).

Which nursing priority applies to an older adult with orthostatic hypotension?

Measure orthostatic vital signs and apply fall precautions, helping the patient rise slowly in stages.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Fainting (MedlinePlus, US National Library of Medicine, 2026); Low blood pressure (MedlinePlus, US National Library of Medicine, 2026).

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Sinoatrial (SA) node highlighted on the Durgical 3D model