Syncope & transient loss of consciousness
Separate reflex syncope from cardiac syncope — echo finds the obstructive and arrhythmic substrates.
Echo approach, step by step
Transient loss of consciousness (TLOC) is syncope, an epileptic seizure, psychogenic, or a rare cause. Syncope is TLOC from cerebral hypoperfusion [196]. The ESC recommends echo when structural heart disease is suspected [196]. Echo is diagnostic in severe AS, obstructive tumours, tamponade, aortic dissection and some congenital anomalies [196].
- Aortic valveVmax, mean gradient, AVA: is AS severe? [5]
- LVOTHypertrophy and SAM, the resting gradient, and Valsalva or standing gradient. Exercise echo for exertional syncope [13,28].
- LVLVEF, scar and aneurysm (substrate for VT) [38].
- RV and PA pressurePE, PH (exertional syncope in PAH), ARVC [8,124,145].
- MassesLA myxoma prolapsing into the mitral valve [176].
- Pericardium and aortaTamponade, dissection [9,149].
- Coronary originsIn young athletes with exertional syncope, look at the origins of the coronaries in PSAX-AV for an anomalous course [150].
- ValvesMS, prosthetic valve obstruction [6,167].
- AV gradient and area
- LVOT gradient (rest and provoked)
- LVEF, scar
- RV, PASP
- Mass
- Pericardium, aorta
- Coronary origins (young, exertional)
Causes & echo clues
| Cause | Echo clue | Next step |
|---|---|---|
| Reflex (vasovagal, situational) | Normal echo | History; tilt test if unclear [196] |
| Orthostatic hypotension | Normal echo; small IVC if hypovolaemic | Standing BP; medication review [196] |
| Bradyarrhythmia | Often normal; conduction disease with amyloid or sarcoid | ECG monitoring, pacing [205] |
| Ventricular tachycardia | Low EF, scar, HCM, ARVC | EP study, ICD [38] |
| Severe aortic stenosis | Calcified valve, Vmax ≥4 m/s | AVR [6] |
| Obstructive HCM | SAM, LVOT gradient on provocation | Treat obstruction; assess SCD risk [13] |
| Pulmonary embolism | RV dilatation and dysfunction | CT pulmonary angiography [124] |
| Pulmonary hypertension | High TR velocity, RV dysfunction | Right-heart catheterisation [8] |
| Atrial myxoma | Mobile LA mass | Surgery [176] |
| Tamponade / dissection | Effusion, flap | Emergency management [9,149] |
Clinical pathway to the diagnosis
- Is it syncope?Complete loss of consciousness, short duration, spontaneous full recovery, loss of postural tone. Exclude seizure, fall and metabolic causes [196].
- Initial evaluationHistory (prodrome, posture, exertion, palpitations), examination with lying and standing BP, and a 12-lead ECG [196].
- Risk stratificationClassify the patient as low or high risk by the ESC features. High-risk patients need ED monitoring or admission [196].
- Targeted testsEcho when structural disease is suspected; ECG monitoring (in-hospital, Holter, loop recorder); carotid sinus massage in patients over 40; tilt test; exercise test for exertional syncope; EP study in selected patients [196].
- Treat the causePacing for bradycardia, ICD or ablation for VT, AVR for AS, and so on [6,38,196,205].
Clinical pearls & pitfalls
PitfallSyncope during exertion is cardiac until proved otherwise. Think of AS, HCM, anomalous coronary artery, PAH and catecholaminergic VT [196].
- Convulsive movements are common in syncope (brief myoclonus). Tongue biting on the side and prolonged confusion favour epilepsy [196].
- Severe AS + syncope is an indication for AVR [6].
- Reduced LVEF + unexplained syncope → evaluate for VT and ICD [38].
- Resting gradient low in HCM? Always provoke. Exertional syncope with a gradient on exercise is treatable [13].
- Old patient, carotid sinus hypersensitivity: pauses >3 s with carotid massage reproduce symptoms [196].
- Echo is low-yield when history, examination and ECG are all normal. Do not use it as a routine screening test [196].
Red flags
- Syncope during exertion or when supine [196]
- Sudden palpitations immediately before the event [196]
- Known structural heart disease or reduced LVEF [196]
- Family history of sudden death under 40 [196]
- Abnormal ECG (conduction disease, pre-excitation, QT, Brugada, ischaemia) [196]
- Chest pain, dyspnoea or new murmur [196]