Ventricular Tachycardia
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Direct answer
Ventricular tachycardia is three or more consecutive ventricular beats, sustained beyond 30 seconds or requiring termination for instability. In any patient with structural heart disease — particularly prior infarction — a broad-complex tachycardia is ventricular tachycardia until proven otherwise. An unstable patient receives synchronised direct-current cardioversion; a stable monomorphic tachycardia is treated with intravenous amiodarone or procainamide; polymorphic tachycardia with a long QT interval is torsades de pointes, treated with intravenous magnesium and correction of the precipitant. Survivors with structural disease need an implantable defibrillator.
What you must remember
- The cardinal rule: mislabelling ventricular tachycardia as supraventricular tachycardia with aberrancy and giving verapamil can precipitate collapse — in structural heart disease, treat as ventricular until proven otherwise; adenosine is acceptable diagnostically in a stable regular broad-complex tachycardia.
- Acute management ladder: pulseless — defibrillation with CPR; unstable with a pulse — synchronised cardioversion under sedation; stable monomorphic — procainamide or amiodarone; correct potassium and magnesium throughout.
- Torsades de pointes: polymorphic tachycardia with twisting axis on a prolonged QT; intravenous magnesium sulphate 1–2 g, stop QT-prolonging drugs, correct electrolytes, and overdrive pacing for bradycardia-dependent episodes; congenital long QT is managed with beta-blockers first.
- Idiopathic ventricular tachycardias: outflow tract tachycardia — left bundle branch block morphology with inferior axis, adenosine-sensitive, excellent ablation outcomes; fascicular tachycardia — right bundle branch block with superior axis, verapamil-sensitive; both in structurally normal hearts.
- Structural substrates: post-infarction scar is the commonest; arrhythmogenic right ventricular cardiomyopathy gives left bundle branch block morphology tachycardia and exercise-related events; bundle branch re-entry in dilated hearts is curable by ablation.
- Electrical storm: three or more episodes in 24 hours — beta-blockade with amiodarone, deep sedation, treat ischaemia and electrolytes, catheter ablation; sympathetic blockade is a rescue option.
- Device and long-term decisions: secondary-prevention defibrillator for sustained tachycardia or arrest with structural disease; primary prevention by ejection fraction criteria; ablation for refractory recurrences.
Common confusion
Pre-excited atrial fibrillation is the great imposter: irregular, broad and very rapid, with AV-nodal blockers contraindicated — cardiovert unstable patients. Torsades must be separated from ischaemic polymorphic tachycardia, which has a normal QT and mandates coronary assessment. Fusion and capture beats, AV dissociation and concordance support ventricular origin, but their absence never proves supraventricular origin.
Exam-focused takeaway
Stems describe a broad-complex tachycardia with a prior infarct and ask either the diagnosis or the first drug; the verapamil distractor is always present. Scenario questions test synchronised versus unsynchronised shock, magnesium for torsades, and verapamil sensitivity for fascicular tachycardia. Post-arrest questions test defibrillator implantation and, in young patients with structurally normal hearts and inferior-axis tachycardia, catheter ablation of an outflow tract focus. Learn the morphology pairs: left bundle with inferior axis for outflow tract, right bundle with superior axis for fascicular.
Frequently asked questions
How should a stable monomorphic broad-complex tachycardia be treated?
With intravenous amiodarone or procainamide while preparing for cardioversion; verapamil and diltiazem are contraindicated because the rhythm is usually ventricular.
How is torsades de pointes managed acutely?
Intravenous magnesium sulphate 1–2 g, withdrawal of QT-prolonging drugs, potassium and magnesium correction, and overdrive pacing for bradycardia-dependent forms.
Why is adenosine acceptable in broad-complex tachycardia?
As a diagnostic agent in a stable regular rhythm — it terminates genuine supraventricular tachycardia with aberrancy and transiently reveals the underlying rhythm without collapsing the patient.
Which idiopathic ventricular tachycardia responds to verapamil?
Fascicular (left posterior fascicle) tachycardia — right bundle branch block morphology with superior axis in a structurally normal heart.
What defines electrical storm and its management?
Three or more ventricular arrhythmia episodes in 24 hours, managed with combined beta-blocker and amiodarone, sedation, ischaemia and electrolyte correction, and catheter ablation at experienced centres.