Preexcited Atrial Fibrillation
Definition and Mechanism
- Preexcited atrial fibrillation (AF) occurs when atrial impulses reach the ventricles through an antegrade-conducting accessory pathway, such as a bundle of Kent.
- The accessory pathway bypasses the normal filtering function of the atrioventricular (AV) node.
- Rapid, irregular ventricular activation can deteriorate into ventricular fibrillation (VF) and sudden cardiac death.
ECG Recognition
- Suspect preexcited AF when the rhythm is:
- Irregularly irregular
- Very rapid (fastest may >250~300/min)
- Wide complex
- Variable in QRS width and morphology from beat to beat
- A shortest preexcited R-R interval of less than 250 ms suggests a rapidly conducting pathway and increased risk of VF.
- A delta wave may be visible during sinus rhythm but may not be obvious during the acute tachyarrhythmia.
Immediate Management
- Assess hemodynamic stability immediately.
- If unstable:
- Perform immediate synchronized electrical cardioversion.
- If stable:
- Use intravenous procainamide or intravenous ibutilide for pharmacologic cardioversion.
- Maintain continuous cardiac and blood pressure monitoring.
- Prepare for synchronized cardioversion if the patient deteriorates or drug therapy fails.
Drugs to Avoid
- Do not administer AV nodal blocking drugs because AV nodal slowing can shift conduction toward the accessory pathway, accelerate the ventricular response, and precipitate VF.
- Contraindicated agents include:
- Adenosine
- Beta blockers
- Diltiazem
- Verapamil
- Digoxin
- Amiodarone
- A common error is treating this rhythm as ordinary AF with rapid ventricular response.
Diagnostic and Treatment Pearls
- An irregular wide-complex tachycardia should trigger consideration of preexcited AF.
- When the diagnosis is uncertain, avoid empiric AV nodal blockade until preexcitation has been excluded.
- Do not rely on ventricular rate control alone. The acute goal is restoration of sinus rhythm without accelerating accessory-pathway conduction.
- After stabilization, obtain cardiology or electrophysiology consultation. Catheter ablation of the accessory pathway is recommended to prevent recurrent preexcited AF and reduce the risk of VF.
Summary Takeaway
- Preexcited AF is a potentially lethal, very rapid, irregular wide-complex tachyarrhythmia.
- Unstable patient: immediate synchronized cardioversion.
- Stable patient: intravenous procainamide or ibutilide.
- Never use AV nodal blockers.
Reference
Joglar JA, Chung MK, Armbruster AL, et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation. Circulation. 2024;149:e1-e156. https://doi.org/10.1161/CIR.0000000000001193
