ConditionHeart & circulation
Syncope (Fainting)
Syncope is the medical term for fainting: a brief loss of consciousness caused by a temporary drop in blood flow to the brain, with full recovery within a minute or two. It is very common, and most faints are vasovagal (triggered by standing, heat, pain or the sight of blood) or due to low blood pressure on standing. Less often, syncope is a sign of a heart rhythm problem or structural heart disease, which can be dangerous. Fainting during exercise, while lying down, or with chest pain needs urgent evaluation.
Also called: Fainting, passing out, blackout, vasovagal syncope, reflex syncope
At a glance
- What it is
- Brief loss of consciousness from reduced brain blood flow, with quick, full recovery.
- Most common types
- Vasovagal (reflex), orthostatic (on standing), situational (coughing, urinating).
- Dangerous types
- Cardiac syncope from arrhythmias or heart disease.
- Red flags
- Faint during exercise or lying down, with chest pain or palpitations, heart disease, family history of sudden death.
- Tests
- History, blood pressure lying and standing, ECG; sometimes heart monitoring, echocardiogram, tilt test.
- Treatment
- Depends on cause: fluids, salt, counter-pressure maneuvers, medicine changes, pacemaker or other heart treatment.
When to get help
Call 911 or go to the ER
- Fainting during exercise, while lying down, or without any warning
- Fainting with chest pain, palpitations, shortness of breath or a severe headache
- Not waking up within a minute or two, confusion that persists, or weakness, numbness or trouble speaking afterward
- Fainting with a serious injury, or vomiting blood or black stools
- Fainting in someone with known heart disease, a pacemaker or ICD, or a family history of sudden death under 50
- In pregnancy with belly pain or bleeding
See a doctor within a day or two
- A first faint in someone over 60
- Repeated faints, or fainting with new medicines (especially blood pressure medicines)
- Fainting with a racing or very slow heartbeat noticed beforehand
Book a routine appointment
- Occasional faints with clear triggers (standing a long time, heat, blood draws) and warning signs, in young healthy people
Usually safe to manage at home
- Feeling faint with known triggers: lie down with legs raised until it passes
What to do if someone faints
- Lay the person flat on their back and raise their legs about 30 cm (12 in) to help blood return to the brain.
- Check breathing. If they are not breathing normally, call 911 and start CPR.
- Loosen tight clothing and give fresh air.
- Let them rest lying down for 10 to 15 minutes after waking, then sit up slowly.
- Do not give food or drink until fully alert.
- Call 911 if they do not wake within 1 to 2 minutes, are injured, have chest pain, or any red flags above.
If you feel faint: sit or lie down immediately, put your head between your knees or raise your legs, or use counter-pressure maneuvers (crossing your legs and tensing them, or gripping your hands and pulling your arms apart).
Types and causes
| Type | Mechanism | Clues |
|---|---|---|
| Vasovagal (reflex) | Sudden drop in heart rate and blood pressure from an exaggerated nerve reflex | Triggers: prolonged standing, heat, pain, fear, blood; warning signs like nausea, sweating, tunnel vision |
| Situational | Reflex triggered by a specific action | Coughing, urinating, swallowing, straining |
| Carotid sinus | Pressure on the neck | Tight collars, turning the head; older men |
| Orthostatic hypotension | Blood pressure drops on standing | Dehydration, blood pressure medicines, diabetes, Parkinson's, older age |
| Cardiac: arrhythmia | Heart beats too slow or too fast | Sudden faint with little warning, palpitations, faint while lying down |
| Cardiac: structural | Heart cannot increase output | Faint on exertion; aortic stenosis, hypertrophic cardiomyopathy |
| Other serious | Reduced output or blood volume | Pulmonary embolism, internal bleeding, aortic dissection |
Cardiac causes in more detail
- bradycardia and heart block
- ventricular tachycardia
- inherited rhythm disorders: long QT syndrome, Brugada syndrome
- heart muscle disease, heart failure, previous heart attack
Syncope vs seizure vs other blackouts
| Syncope | Seizure | |
|---|---|---|
| Warning | Lightheaded, sweaty, nauseated, vision fading | Aura possible, or none |
| Color | Pale | Often flushed or blue |
| Movements | Brief jerks possible (under 15 seconds) | Prolonged rhythmic jerking |
| Tongue bite | Uncommon, tip of tongue | Side of tongue, common |
| Recovery | Quick, alert within a minute or two | Confusion and drowsiness for minutes to hours |
Low blood sugar, intoxication, head injury and functional (psychogenic) episodes can also cause blackouts.
Evaluation
Every person who faints should have:
- A detailed history from the person and witnesses: triggers, position, warning signs, duration, recovery, medicines, family history.
- Examination, including blood pressure lying and standing.
- An ECG.
Further tests depend on the findings:
- blood tests: blood count, electrolytes, blood sugar, pregnancy test
- echocardiogram for suspected structural heart disease
- heart rhythm monitoring: Holter (24 to 48 hours), patch monitors (up to 2 weeks), event monitors, or an implantable loop recorder for infrequent episodes
- exercise stress test for faints during exertion
- tilt table test for suspected reflex syncope
- EEG or brain imaging only if a seizure or neurological cause is suspected
Treatment
Vasovagal and orthostatic syncope
- recognize and avoid triggers
- drink plenty of fluids (about 2 to 3 liters a day unless restricted) and, if advised, increase salt intake
- counter-pressure maneuvers at the first warning signs
- stand up slowly; avoid prolonged standing
- review medicines that lower blood pressure
- compression stockings or abdominal binders
- medicines such as fludrocortisone or midodrine in selected cases
Cardiac syncope
- pacemaker for slow heart rhythms
- implantable cardioverter-defibrillator (ICD) or catheter ablation for dangerous fast rhythms
- valve replacement for severe aortic stenosis
- treatment of the underlying heart disease
Driving
Many places restrict driving after unexplained syncope or cardiac syncope until the cause is treated. Ask your doctor about local rules.
Frequently asked questions
What is syncope?
Syncope is the medical term for fainting: a short loss of consciousness caused by temporarily reduced blood flow to the brain. The person falls, then wakes within about a minute and recovers fully. It has many causes, from harmless reflexes to heart problems.
What is the most common cause of fainting?
The most common cause is vasovagal syncope, a reflex that drops heart rate and blood pressure in response to triggers like standing for a long time, heat, pain, stress or seeing blood. It is usually harmless.
When should I worry about fainting?
Seek urgent care if fainting happens during exercise or while lying down, without warning, with chest pain, palpitations or breathlessness, after a head injury, in someone with heart disease, or with a family history of sudden death at a young age.
How is the cause of syncope found?
Doctors start with a detailed history, physical exam, blood pressure lying and standing, and an ECG. Depending on the findings, they may order blood tests, an echocardiogram, heart rhythm monitoring, an exercise test or a tilt table test.
How can I stop myself from fainting?
At the first warning signs, lie down with your legs raised or sit with your head low. Cross your legs and tense your muscles, or clench your fists. Drink plenty of fluids, avoid triggers, and stand up slowly. See a doctor to confirm the cause.
Sources
This guide was written from current patient and clinical guidance, including:
- American College of Cardiology, American Heart Association and Heart Rhythm Society: Guideline for the evaluation and management of patients with syncope
- European Society of Cardiology: Guidelines for the diagnosis and management of syncope
- MedlinePlus: Fainting
- NHS: Fainting
- American Academy of Family Physicians (AAFP): Syncope, evaluation and differential diagnosis