Atrial fibrillation with bundle‑branch block (irregular broad‑complex tachycardia)
An irregular broad‑complex tachycardia may represent atrial fibrillation (AF) with a coexisting bundle‑branch block (BBB) or transient ventricular aberrancy, pre‑excited AF via an accessory pathway (WPW), or ventricular tachycardia. Rapid recognition, assessment of haemodynamic stability and early appropriate escalation are essential.
Presentation
- AF with a coexisting fixed BBB or with transient ventricular aberrancy produces an irregularly irregular rhythm with broad QRS complexes.
- Pre‑excited AF (accessory pathway / WPW) can mimic polymorphic VT and may degenerate to ventricular fibrillation (VF).
- Symptoms range from palpitations and breathlessness to syncope, chest pain or haemodynamic collapse.
- Examination typically shows an irregularly irregular pulse.
Pathophysiology (concise)
- AF: chaotic atrial activity with an irregular ventricular response determined by conduction pathways.
- Fixed BBB: intraventricular conduction delay widens QRSs; morphology is usually consistent across beats.
- Ventricular aberrancy: rate‑dependent conduction delay (e.g., Ashman phenomenon) produces intermittent broad complexes.
- Pre‑excited AF: an accessory pathway conducts impulses to the ventricles, bypassing AV nodal rate‑limiting properties → very rapid, irregular, often polymorphic wide QRS complexes with high risk of VF.