Collapse and syncope
Most faints are harmless. Your job is to find the few that are not: the heart, bleeding, PE, and the bleeding brain. A good story from a witness and an ECG find most of them.
A 24-year-old man collapsed suddenly while playing cricket and was "out" for about 20 seconds. He had no warning. He is now alert and wants to go home. Pulse 64, BP 124/76. His uncle died suddenly at 35.
Is this a simple faint?
- A to E and full observationsIncluding lying and standing BP.
- 12-lead ECGEvery patient. Look for the dangerous patterns.
- Blood sugarLow sugar causes collapse.
- A witness accountWhat happened before, during and after.
- BloodsCBC (hidden bleeding), electrolytes, creatinine. Troponin only if chest pain or ECG changes.
- Pregnancy testWomen of child-bearing age.
- Rectal examinationIf anaemic or melaena is possible.
- Decide the riskHigh-risk features: admit or cardiology review. Low risk: home with advice.
- Collapse during exercise or while lying down
- No warning, with injury
- Chest pain, breathlessness or palpitations with it
- Family history of sudden death under 40
- New murmur or abnormal ECG
- Low Hb or melaena
- Arrhythmia (heart block, VT, long QT, WPW, Brugada)
- Aortic stenosis or HOCM
- Pulmonary embolism
- Aortic dissection or ruptured AAA
- Hidden bleeding (GI, ectopic)
- Subarachnoid haemorrhage
| Low sugar | 10% dextrose 150–200 mL IV, then food |
| Postural drop | Systolic fall of 20 or more, or diastolic of 10 or more, within 3 minutes of standing |
| Exercise or lying down | Collapse during exertion or lying flat is cardiac until proven otherwise |
| ECG | Every patient, no exceptions |
| Family history | Sudden death under 40: high risk |
Check every dose against a current drug reference and your hospital protocol.
On this page
Faint, fit, or something else?
- Before: standing, hot, pain, light-headed, sweaty, vision greying
- During: brief, a few jerks possible
- After: quick recovery, pale
- Before: no trigger, aura
- During: stiff then rhythmic jerking, tongue bitten on the side, cyanosis
- After: confused for minutes to hours
- No warning, or palpitations or chest pain first
- During exercise or lying down
- Quick recovery but may be injured
A few jerks during a faint are common and do not mean a fit. A long period of confusion afterwards, a bitten side of the tongue and a known epilepsy history point to a seizure.
Causes
| Group | Causes |
|---|---|
| Reflex (vasovagal, situational) | Standing long, heat, pain, fear, coughing, passing urine. Most common. Harmless |
| Postural (orthostatic) hypotension | Dehydration, BP tablets, diuretics, diabetes, Parkinson's, alcohol, bleeding |
| Cardiac: arrhythmia | Heart block, VT, sick sinus, long QT, Brugada, WPW |
| Cardiac: structural | Aortic stenosis, hypertrophic cardiomyopathy (HOCM), PE, tamponade, dissection |
| Not syncope | Low sugar, seizure, stroke or TIA (rarely causes collapse), subarachnoid haemorrhage, intoxication |
The ECG you must read
- Heart block: Mobitz II, complete heart block, or bifascicular block.
- Long QT (QTc above 470 ms in men, 480 in women) or short QT.
- Pre-excitation (WPW): short PR and a delta wave.
- Brugada pattern: coved ST elevation in V1–V2.
- Signs of HOCM: large voltages, deep narrow Q waves.
- Ischaemia, or a new arrhythmia.
- Very slow sinus rate (below 40) or pauses when awake.
Use the QTc calculator if unsure.
High risk or low risk?
- Collapse during exertion or lying down
- No warning, with injury
- Chest pain, palpitations, breathlessness
- Abnormal ECG
- Heart disease or new murmur
- Family history of sudden death under 40
- Low Hb, low BP that does not recover
- Typical faint with clear trigger and warning
- Normal examination and ECG
- Young, no heart disease
- Advice and follow-up as needed
Investigations
| Test | Why |
|---|---|
| ECG | Every patient |
| Lying and standing BP | Postural hypotension |
| Blood sugar | Low sugar |
| CBC | Hidden bleeding |
| Electrolytes, creatinine | Dehydration, potassium, magnesium |
| Pregnancy test | Ectopic |
| Troponin | Only with chest pain or ischaemic ECG |
| Echo | Murmur, abnormal ECG, exertional syncope |
| Holter or longer monitoring | Suspected arrhythmia |
| CT head | Only if head injury, focal signs, or SAH suspected. Not routinely for syncope |
Advice for a simple faint
- Recognise the warning signs. Sit or lie down with legs up straight away.
- Drink enough fluid, especially in summer.
- Avoid standing still for long in heat.
- Review BP tablets and diuretics in older patients.
- Driving: no restriction after a simple faint with a clear trigger while standing. Seek advice for anything else.
Common mistakes
- Calling every collapse a "vasovagal" without an ECG.
- Missing exertional syncope in a young athlete with a family history.
- Ordering a CT head for every faint.
- Calling a few jerks a seizure and starting epilepsy medicine.
- Missing melaena or an ectopic.
- Forgetting the lying and standing BP in an elderly patient on many tablets.
Frequently asked questions
What are the red flags in syncope?
Collapse during exercise or lying down, no warning with injury, chest pain or palpitations, an abnormal ECG, heart disease or a new murmur, family history of sudden death under 40, and signs of bleeding.
How is a faint different from a seizure?
A faint usually has a trigger and warning (light-headedness, sweating), lasts seconds, and recovery is quick. A seizure often has no trigger, stiffness then rhythmic jerking, a bitten side of the tongue, and confusion lasting minutes or longer.
Does every patient with syncope need a CT head?
No. CT is only needed with head injury, focal neurological signs, or suspected subarachnoid haemorrhage.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 24-year-old collapsed without warning while playing cricket. His uncle died suddenly at 35. What is the best plan?
Answer: ECG, echo and cardiology. Syncope during exertion or with a family history of sudden death suggests cardiac causes such as cardiomyopathy or channelopathy.
- CT head: Not the priority.
- Discharge as a simple faint: Exertional syncope with family history is high risk.
- EEG: Not the first test.
- Reassure and advise fluids: Not enough.
2. An ECG after a collapse shows a short PR interval and a slurred upstroke of the QRS. What is it?
Answer: Pre-excitation (WPW). A delta wave and short PR indicate an accessory pathway. Refer to cardiology.
- Brugada pattern: Different.
- First-degree heart block: PR is long in that.
- Left bundle branch block: Different pattern.
- Long QT: Not this.
3. A collapse was followed by 30 minutes of confusion and the patient bit the side of the tongue. What is likely?
Answer: Seizure rather than syncope. Prolonged post-ictal confusion and lateral tongue biting suggest a seizure.
- Cardiac arrhythmia: Usually quick recovery.
- Hypoglycaemia only: Possible, check sugar, but the features suggest seizure.
- Vasovagal syncope: Recovery is quick.
- Orthostatic hypotension: Quick recovery.
4. A 20-year-old student faints while standing in a hot crowded assembly, after feeling nauseated, sweaty and light-headed. She recovers within a minute with no confusion. ECG is normal. What is the diagnosis?
Answer: Vasovagal syncope. Reflex (vasovagal) syncope: triggered by prolonged standing, heat, pain, emotion; prodrome of nausea, sweating, pallor, light-headedness; brief loss of consciousness with rapid recovery. Normal ECG and examination → reassurance, education (avoid triggers, counter-pressure manoeuvres, hydration). Red flags for cardiac syncope: exertional, chest pain/palpitations, family history of sudden death, abnormal ECG (long QT, Brugada, WPW, heart block), structural heart disease.
- Epileptic seizure: A seizure causes prolonged post-ictal confusion.
- Cardiac arrhythmia: Arrhythmia causes exertional syncope or syncope without warning.
- Hypoglycaemia: Hypoglycaemia recovers slowly and needs glucose.
5. An 80-year-old has syncope. ECG shows P waves at 80/min and regular broad QRS complexes at 35/min with no relationship between them. What is the definitive treatment?
Answer: Permanent pacemaker. Third-degree (complete) heart block: AV dissociation with a slow escape rhythm. Broad escape (ventricular) is unstable. Acute: atropine 500 µg (up to 3 mg), isoprenaline/adrenaline infusion, transcutaneous pacing; definitive treatment is a permanent pacemaker. Causes: degeneration (Lenègre/Lev), inferior MI (often transient), drugs (beta-blockers, digoxin), Lyme, infiltrative disease. Mobitz II also needs pacing.
- Repeated atropine doses: Atropine is a temporary measure.
- Beta-blocker: Beta-blockers worsen bradycardia.
- Observation on the ward: Complete heart block with syncope carries a high risk of asystole.
6. A young athlete collapses and dies during exercise. Autopsy shows asymmetric septal hypertrophy with myocyte disarray. What is the diagnosis?
Answer: Hypertrophic cardiomyopathy. HCM is usually autosomal dominant (β-myosin heavy chain, myosin-binding protein C mutations): asymmetric septal hypertrophy, myofibre disarray, dynamic LV outflow obstruction (murmur increases with Valsalva, decreases with squatting), diastolic dysfunction and sudden death in young athletes. Dilated cardiomyopathy: dilated chambers, systolic failure (alcohol, viral, peripartum, genetic).
- Dilated cardiomyopathy: Dilated, thin walls.
- Restrictive cardiomyopathy: Stiff walls (amyloid).
- Arrhythmogenic RV cardiomyopathy: Fibrofatty RV.
- Viral myocarditis: Inflammatory infiltrate.
7. A 72-year-old has exertional chest pain and fainted while climbing stairs. He has a slow-rising pulse and an ejection systolic murmur radiating to the carotids. Why does exertion cause syncope?
Answer: Fixed outflow cannot raise output. In severe aortic stenosis the narrowed valve limits stroke volume. During exercise, muscle vasodilatation lowers systemic resistance, but cardiac output cannot rise enough, so blood pressure falls and brain perfusion drops, causing syncope. The thick ventricle needs more oxygen while coronary perfusion is reduced, causing angina. Symptomatic severe aortic stenosis needs valve replacement.
- Mitral valve prolapses: Not the lesion.
- Coronary arteries dilate too much: Not the mechanism.
- Pulmonary pressure falls: Not the mechanism.
- Heart rate falls during exercise: Heart rate rises.
References and dose sources
- ESC 2018 guidelines on syncope
- NICE CG109: Transient loss of consciousness in over 16s
- NICE NG158 — VTE
- NICE NG156 — AAA
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.