Torsade de Pointes (TdP)
Definition and recognition
- Torsade de Pointes (TdP) is a form of polymorphic ventricular tachycardia classically associated with a prolonged QT interval.
- On monitor or 12‑lead ECG the QRS morphology changes rapidly and appears to “twist” around the baseline.
- TdP may cause syncope, haemodynamic collapse, or degenerate into ventricular fibrillation and can be mistaken for VF when very rapid (Resuscitation Council UK).
Pathophysiology
- Prolonged ventricular repolarisation (long QT) predisposes to early after‑depolarisations (EADs) and triggered activity, which can initiate runs of polymorphic VT.
- Bradycardia, low serum potassium or magnesium, drugs that block repolarising potassium currents, and congenital long QT syndromes all increase risk.
Common causes and precipitants
- Congenital long QT syndromes (channelopathies).
- Acquired QT prolongation in common ED contexts:
- QT‑prolonging drugs (examples: some antiemetics such as IV ondansetron; macrolide antibiotics; some fluoroquinolones; many antipsychotics and some antidepressants - e.g. citalopram/escitalopram dose limitations; domperidone; hydroxyzine; high‑dose/overdose loperamide; methadone). Check MHRA drug safety updates for drug‑specific guidance (MHRA).
- Electrolyte disturbance: hypokalaemia, hypomagnesaemia, and sometimes hypocalcaemia.
- Bradycardia, pauses, or advanced AV block.
- Acute ischaemia and toxicological overdoses (RCEM).