Irregular broad‑complex tachycardia (IBCT)
Irregular broad‑complex tachycardia is an ECG pattern, not a single diagnosis. It most commonly reflects one of three emergencies that require different treatments: pre‑excited atrial fibrillation (AF with an accessory pathway, e.g. WPW), torsade de pointes (polymorphic VT on a prolonged QT), or AF with bundle branch block/aberrancy.
When the mechanism is uncertain, treat as ventricular tachycardia (VT) - VT is the immediately life‑threatening rhythm you must not miss (Resuscitation Council UK adult tachyarrhythmia algorithm).
Immediate priorities
- Rapidly assess haemodynamic stability. Life‑threatening features include shock or hypotension, syncope, ongoing ischaemia, acute pulmonary oedema, severe breathlessness, altered conscious level, or immediate post‑ROSC.
- If unstable, perform synchronised cardioversion immediately. Do not delay for drugs. Sedate if there is time and it is safe; follow local ALS energy and synchronisation protocols (RCUK ALS).
- If stable, rapidly characterise the rhythm (ECG pattern, comparison with prior ECGs, history of WPW/AF, rate, onset, medications, electrolytes).
- Therapy is subtype‑specific; if doubt remains, treat as VT.
Distinguishing the common causes - practical ECG clues
- Pre‑excited AF (AF with accessory pathway, e.g. WPW)
- Rhythm is irregularly irregular with very rapid ventricular rates (often >180-200 bpm).
- QRS morphology and width are variable because conduction alternates between the AV node and the accessory pathway; classic delta waves may be absent during AF.
- Short RR intervals and very...