⚡ Key rule: Any regular broad-complex tachycardia should be treated as VT until proven otherwise. If the patient is unstable, act first (shock) and diagnose later.

📖 Broad-Complex Tachycardia (BCT)

Broad QRS = QRS duration >120 ms (>3 small squares).
BCT = tachycardia with broad QRS complexes. The big fork in the road is regular vs irregular.
Why it matters: VT can rapidly deteriorate into VF/cardiac arrest, so early, safe decision-making is crucial.

📊 Causes of BCT (regular vs irregular)

Pattern	Likely causes	High-risk “don’t miss”
Regular BCT	Monomorphic VT (commonest) SVT with aberrancy (pre-existing BBB or rate-related BBB) Atrial flutter with fixed conduction + aberrancy Antidromic AVRT (WPW) (rare)	VT (assume VT until proven otherwise)
Irregular BCT	AF with aberrancy Pre-excited AF (WPW) Polymorphic VT / torsades de pointes	Pre-excited AF (WPW) (can degenerate into VF) Torsades (QT-related, can deteriorate)

🩺 First 30 seconds: assess stability

Unstable features: shock, syncope, ongoing chest pain/MI features, acute heart failure/pulmonary oedema, severe hypotension.
If unstable with a pulse: synchronised DC cardioversion (sedate if conscious and time allows).
If pulseless VT/VF: follow ALS cardiac arrest (defibrillation + CPR).

🔎 ECG clues that favour VT

ECG/clinical clue	Why it points to VT	What you do with it
AV dissociation (P waves “march through” independently)	Atria and ventricles are being driven by different pacemakers	Treat as VT; urgent senior/cardiology input
Capture beats (a single narrow QRS during BCT)	Occasional supraventricular impulse conducts to ventricle amid VT	Strong VT support
Fusion beats (hybrid QRS morphology)	Simultaneous ventricular activation from sinus + ventricular focus	Strong VT support
Known structural heart disease / prior MI	Scar-related re-entry VT is common in this group	Lower your threshold to shock / treat as VT

🧪 Investigations (don’t delay treatment if unstable)

12-lead ECG (if stable) + continuous monitoring.
Bloods: U&E, Mg, Ca, glucose, FBC, troponin (if ACS possible) ± ABG/VBG if unwell.
Echo later to assess LV function/structural disease (especially if VT suspected).

⚕️ Management table (Resus Council UK–aligned approach)

Scenario	Immediate action	Key “don’ts”
Unstable BCT with a pulse	Synchronised DC cardioversion (urgent) Correct reversible causes (K/Mg/ischaemia, drug toxicity)	Don’t “watch and wait” Don’t delay cardioversion for prolonged diagnostics
Stable regular BCT	Treat as VT unless strong evidence otherwise Consider amiodarone IV 300 mg over 20–60 min, then infusion if needed (local protocol) Adenosine may be used diagnostically/therapeutically only in regular rhythms where SVT with aberrancy is plausible and expert support is available	Do not use adenosine in irregular broad-complex tachycardia
Stable irregular BCT	Think: AF with aberrancy vs pre-excited AF vs torsades Get senior/cardiology help early; treat reversible causes	Avoid AV-nodal blockers if pre-excited AF suspected (risk of VF)
Torsades de pointes (polymorphic VT + prolonged QT)	Correct causes: stop QT-prolonging drugs, correct K/Mg IV magnesium (commonly 2 g over ~10 min, then reassess; local policy) If unstable: DC cardioversion	Don’t ignore QT prolongation (it’s the mechanism)

🧠 Rhythm snapshots (high-yield)

Monomorphic VT: usually regular, broad QRS, often post-MI scar-related; can present with palpitations, syncope, or shock.
VF / pulseless VT: cardiac arrest rhythms → ALS shockable pathway (defib + CPR).
Pre-excited AF (WPW): irregularly irregular, very fast, varying QRS morphologies; avoid AV-nodal blockers and seek urgent expert help.

🌟 Clinical teaching point: The danger in BCT is mislabelling VT as “SVT with BBB” and giving the wrong therapy. When myocardium is ischaemic or scarred, re-entry circuits make VT more likely; the longer it runs, the more likely it becomes haemodynamically unstable. That’s why UK algorithms prioritise stability → shock if needed → antiarrhythmic strategy, rather than perfect rhythm diagnosis first. :contentReference[oaicite:8]{index=8}

📚 References (UK + core)

Resuscitation Council UK: Tachycardia (with pulse) algorithm (peri-arrest guidance, cardioversion/antiarrhythmic approach).
Resuscitation Council UK: Peri-arrest arrhythmias (ALS educational material).
ESC: 2022 guidelines on ventricular arrhythmias & sudden cardiac death prevention (context for VT risk in structural heart disease). :contentReference[oaicite:11]{index=11}

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Broad Complex Tachycardia