Pre‑Excited Atrial Fibrillation
Overview
Pre‑excited atrial fibrillation (AF with an accessory pathway, e.g. Wolff‑Parkinson‑White) occurs when atrial fibrillation conducts to the ventricles partly or wholly via an accessory pathway. The ECG shows an irregularly irregular, often very fast, broad‑complex tachycardia with beat‑to‑beat variation in QRS morphology.
It is potentially life‑threatening because interventions that slow or block the AV node can paradoxically increase conduction down the accessory pathway, producing extreme ventricular rates, haemodynamic collapse or ventricular fibrillation.
Guidance sources
- UK national AF guidance (NICE NG196) covers AF diagnosis and referral, but acute ED recognition and immediate management of pre‑excited AF are best guided by Resuscitation Council UK ALS/tachycardia teaching and RCEMlearning ECG resources.
- Consult local cardiology protocols for specific drug dosing and local availability.
Pathophysiology - why it is dangerous
- In AF the atria fire chaotically and irregularly.
- The AV node normally limits ventricular response because of its longer refractory period.
- An accessory pathway (often an atrioventricular bypass tract) may have a shorter refractory period and can conduct rapid atrial impulses to the ventricles.
- If AV nodal conduction is slowed or blocked (for example by drugs or vagal manoeuvres), a greater proportion of impulses may travel via the accessory pathway.
- This can produce very fast ventricular rates (>200 bpm) and increases the risk of degeneration to ventricular fibrillation.