Syncope: Risk Stratification and Red Flags

Syncope is a loss of consciousness. It is brief, it comes on fast, and the patient wakes up on their own because the brain got too little blood. The ED and EMS job is not to name the faint. Find the few whose cause can kill them within 30 days. Send the rest home safely.

• Reflex (neurally mediated): vasovagal syncope, carotid sinus hypersensitivity and situational events like micturition, defecation, prolonged standing or cough. This is the most common cause. Patients usually have a prodrome of nausea, diaphoresis or light-headedness.
• Orthostatic: postural hypotension with symptoms (SBP fall of 20 mmHg or more, or DBP fall of 10 mmHg or more, within 3 minutes of standing, or SBP under 90 mmHg on standing). Volume loss from poor intake or GI losses drives it. So do autonomic dysfunction and medications such as vasodilators and excessive diuretics. It is more likely in older adults and in pregnancy.
• Cardiac: bradyarrhythmia or tachyarrhythmia, channelopathy (Brugada, long QT, short QT) and structural disease (aortic stenosis, cardiomyopathy, tamponade). Framingham cohort: cardiac syncope carried a hazard ratio of 2.01 for death from any cause, compared with people without syncope. Vasovagal syncope, by contrast, was not associated with increased cardiovascular morbidity or mortality.
• Other serious causes: pulmonary embolism, hemorrhage (GI or internal), ectopic pregnancy and subarachnoid hemorrhage. Don't let these slip past you.

Typical and High-Risk Presentations

• Typical reflex event: a prodrome on standing. Warmth or pain. Pallor and sweating. Quick recovery, then a normal neurologic exam.
• Exertional syncope: it happens during exercise or exertion. Think aortic stenosis and arrhythmia.
• Syncope with injury or post-event focal deficit: A true syncope leaves a normal neurologic exam. A focal deficit or prolonged confusion means a stroke or seizure evaluation.

Red Flags

• Exertional or supine onset: it hits during exertion or while lying down.
• Sudden palpitations before the faint. Or chest pain, dyspnea or palpitations with the event.
• Known structural heart disease (aortic stenosis, hypertrophic or other cardiomyopathy), heart failure or a history of heart disease.
• Family history of sudden cardiac death, cardiomyopathy or inherited arrhythmia (channelopathy).
• Implanted pacemaker or ICD with an event: interrogate the device.
• Systolic BP <90 or >180 mmHg; hematocrit <30%.
• Troponin above the 99th percentile for the normal population.
• A focal neurologic deficit. Or suspicion of GI bleeding (melena, positive hemoccult).

ECG Red Flags

• Mobitz II, complete AV block, or sinus bradycardia under 40/min (awake) or pauses over 3 s.
• Brugada pattern, pre-excitation, or HCM or ARVC features (such as an epsilon wave).
• Long QT (QTc ≥500 ms on the E3 QT-interval page; the CSRS counts QTc over 480 ms) or short QT.
• QRS over 130 ms, or bifascicular block.
• Sustained or non-sustained VT, rapid atrial fibrillation, or ischemic changes.
• QT-prolonging drugs, or low potassium or magnesium. Correct it, then repeat the ECG.

Risk Tools

• Use and limits: Both tools support clinical judgment. Neither replaces it. In an individual patient data meta-analysis, the tools were not more accurate than clinical judgment for short-term serious outcomes.
• San Francisco Syncope Rule (SFSR): any one of these makes it high risk: history of congestive heart failure, hematocrit under 30%, abnormal ECG, shortness of breath, or systolic BP under 90 mmHg. In the derivation cohort it was 96% sensitive and 62% specific for serious outcomes within 7 days. The first number is how often it catches the dangerous ones. The second is how often it correctly clears the rest.
• Canadian Syncope Risk Score (CSRS): an ED tool that predicts 30-day serious adverse events: arrhythmia, MI, structural disease, PE, serious hemorrhage, procedural intervention, death. It uses nine predictors: vasovagal predisposition, heart disease, SBP <90 or >180 mmHg, troponin above the 99th percentile, abnormal QRS axis, QRS over 130 ms, QTc over 480 ms, and ED diagnoses of cardiac or vasovagal syncope. Scores run from −3 to 11. In derivation, 30-day risk climbed from 0.4% at −3 to 83.6% at 11. In validation, a threshold of −1 or higher had 97.8% sensitivity and 44.3% specificity for 30-day serious outcomes. Those two figures, 97.8% and 44.3%, belong to the −1 screening cut-off and no other. The source's discharge guidance for its very-low and low bands is separate. Band cut-offs are not given here, so apply the validated bands from the source and local protocol.

• Seizure: Look for tongue or cheek laceration, incontinence, prolonged post-event confusion or a witnessed convulsion. A true syncope does not carry a prolonged postictal state.
• Hypoglycemia: every patient with altered mental status after an event gets a glucose check.
• Stroke or TIA: any focal deficit means a stroke pathway. Not syncope.
• Hypovolemia and medication effect: GI losses, diuretics, vasodilators or sedatives. Orthostatic vitals help sort it out.
• Intoxication: alcohol, opioids or sedatives. Check glucose, and treat airway and breathing first.

1. Scene safety and ABCs: confirm the patient is breathing and perfusing; treat any injury.
2. Position: supine, with legs raised if hypotensive, per protocol. Do not let the patient stand or walk to test them.
3. Oxygen and monitor: titrate oxygen to saturation target per protocol; apply the cardiac monitor.
4. Take the history: prodrome, exertion or supine onset, chest pain, dyspnea, palpitations, duration, witnesses, seizure features, last oral intake and medications (vasodilators, diuretics, antiarrhythmics, insulin or sulfonylureas).
5. Glucose: check if the protocol allows; treat hypoglycemia per the BLS protocol.
6. Transport priority: any syncope with a red flag, abnormal ECG or injury is a transport decision; do not discharge at the scene.

Doses vary by protocol; follow local protocols and medical direction.

• Access and 12-lead ECG (Paramedic/RN/CCT): IV or IO access, cardiac monitor and 12-lead ECG. See 12-Lead ECG Acquisition. Any abnormal ECG is a high-risk feature.
• Symptomatic bradycardia: atropine 1 mg IV/IO, repeat every 3–5 min (max 3 mg). See Atropine. Atropine is unlikely to help Mobitz II or complete block: do not delay pacing. Caution: doses under 0.5 mg can cause paradoxical bradycardia; atropine is ineffective in a transplanted (denervated) heart; use caution in acute coronary ischemia or MI. See the Atropine page for the full list.
• Bradycardia that does not respond: epinephrine infusion as a bridge (see Epinephrine IV) or dopamine (see Dopamine), and transcutaneous pacing (Paramedic/RN/CCT) per Transcutaneous Pacing.
• Tachycardia with syncope: follow the Adult Tachycardia pathway, including synchronized cardioversion for unstable rhythms (Paramedic/RN/CCT, per local protocol).
• Symptomatic hypoglycemia (glucose under 70 mg/dL with altered mental status or symptoms): dextrose 10–25 g IV (for example D50W 25 g = 50 mL, or D10W 100 mL = 10 g). Give D50W through a patent large vein and confirm IV placement; concentrated dextrose causes extravasation and phlebitis. Recheck glucose about 15 min after each dose and repeat if it is still under 70 mg/dL or symptoms persist (see Dextrose).
• Hypotension from volume loss or reflex: isotonic crystalloid bolus with reassessment after each bolus (see Normal Saline); stop when lungs or oxygenation worsen.
• Pulseless rhythm or arrest: start the Adult Cardiac Arrest pathway.

• Cardiac: telemetry, serial troponin and transthoracic echocardiogram when the ECG is abnormal or structural heart disease is suspected. Cardiology or electrophysiology consult for Mobitz II, complete block, sustained VT or severe aortic stenosis.
• Neuroimaging and EEG: Skip routine head CT, carotid imaging and EEG in uncomplicated syncope without a focal deficit or head trauma (2017 ACC/AHA/HRS).
• Anticoagulated patients and head injury after a fall: keep your threshold for head imaging low. The injury may be occult.
• Possible PE: follow the Pulmonary Embolism pathway.
• Possible aortic dissection: follow the Aortic Dissection pathway, per local protocol.
• Possible bleeding: repeat hematocrit, type and screen, GI consult for melena or positive hemoccult. See Hemorrhagic Shock if unstable.
• Disposition: Pair the CSRS or SFSR result with the ECG and troponin. In the 2020 validation, very-low and low CSRS risk patients could generally be discharged. High risk warrants monitoring. Brief hospitalization may be considered.

• Destination: pick a monitored ED with cardiology and pacing available for any bradyarrhythmia, abnormal ECG or hypotension. Transport to the nearest appropriate facility per local protocol.
• In transit: continuous rhythm monitoring. Pads on for symptomatic bradycardia. Reassess pulse, BP, glucose and mental status at each interval.
• Handoff: ECG copy, glucose, orthostatic vitals, medications given with times and doses, the event history (prodrome, exertion, duration), and the red flags present.
• Equipment: atropine, epinephrine infusion and pacing pads ready (Paramedic/RN/CCT).

• Pediatrics: most pediatric syncope is reflex. Red flags in children: exertional syncope, congenital or structural heart disease, family history of sudden death, and an abnormal ECG (long or short QT, Brugada pattern, pre-excitation). For bradycardia with poor perfusion, oxygenate and ventilate first. Start compressions if HR stays under 60/min despite this. Epinephrine IV/IO 0.01 mg/kg (0.1 mL/kg of 1:10,000, every 3–5 min) is first line (see Epinephrine IV). Use atropine 0.02 mg/kg IV/IO (minimum 0.1 mg, maximum 0.5 mg per dose, may repeat once) for increased vagal tone or primary AV block (see Atropine). Work from Weight-Based Dosing and Vital Signs. Follow the AHA 2025 PALS guidance and local protocol, and consult pediatric cardiology per local protocol.
• Pregnancy: In pregnancy, orthostatic syncope is more likely. After about 20 weeks, supine hypotensive syndrome (aortocaval compression) is a common cause of hypotension and syncope: put the patient in left lateral position, or move the uterus to the left by hand. Every woman of childbearing age with syncope gets a pregnancy test. A positive test with pain or bleeding needs urgent evaluation for ectopic pregnancy, placental abruption and hemorrhage, with OB and fetal assessment. Treat hypotension per protocol. Standard resuscitation drugs and doses apply in pregnancy. Don't withhold them.
• Older Adults: In older adults, orthostatic syncope is more likely. Check orthostatic vitals and review vasodilator, diuretic and sedative use. Falls and head injury get a separate trauma assessment.

• Error: calling it vasovagal with no 12-lead ECG and no troponin. Get the ECG first. Then assign the reflex label.
• Error: waiting on atropine in Mobitz II or complete heart block. Pace. Atropine may not help.
• Error: giving atropine to a heart transplant recipient, or making it the first drug in pediatric bradycardia with poor perfusion. Ventilate and oxygenate first. In children, epinephrine is first line.
• Error: blaming a focal deficit or prolonged confusion on syncope. Treat it as stroke or seizure until excluded.
• Error: anchoring on reflex syncope when there are exertional symptoms or a murmur. Keep the cardiac causes open.
• Error: missing PE, GI bleeding or ectopic pregnancy because the patient is now well. Recovering hemodynamically does not rule out a serious cause.
• Error: discharging a high-risk patient on normal vitals alone. Apply the SFSR and CSRS inputs. Document them.