U01.07.020 Torsades de pointes

Torsades de pointes (TdP) is a polymorphic ventricular tachycardia characterized by shifting sinusoidal waveforms on electrocardiogram (ECG). It can progress to ventricular fibrillation (VF) and lead to sudden cardiac death if not promptly treated.

Etiology

A prolonged QT interval predisposes individuals to TdP. The most common causes include:

Medications (Drug-induced long QT syndrome)
Electrolyte abnormalities (↓ K+, ↓ Mg²⁺, ↓ Ca²⁺)
Congenital long QT syndromes (genetic mutations affecting ion channels)

ECG Features

Polymorphic ventricular tachycardia
Sinusoidal waveform pattern with twisting QRS complexes
Prolonged QT interval preceding the arrhythmia

Causes of Drug-Induced Long QT Syndrome

The mnemonic “ABCDE” helps remember the drugs associated with QT prolongation:

Category	Examples
Antiarrhythmics	Class IA (quinidine, procainamide), Class III (amiodarone, sotalol)
Biotics (Antibiotics)	Macrolides (e.g., erythromycin, clarithromycin)
Cychotics (Antipsychotics)	Haloperidol, risperidone
Depressants (Antidepressants)	Tricyclic antidepressants (TCAs)
Emetics (Antiemetics)	Ondansetron

Treatment

First-line therapy: Magnesium sulfate (even if Mg²⁺ levels are normal)
Correct underlying causes:
- Stop offending drugs
- Normalize electrolyte imbalances (K+, Mg²⁺, Ca²⁺)
- Consider beta-blockers for congenital cases

Congenital Long QT Syndrome

Inherited disorders affecting myocardial repolarization due to ion channel mutations (most commonly K+ channel loss-of-function mutations). These conditions increase the risk of sudden cardiac death (SCD) due to torsades de pointes.

Types of Congenital Long QT Syndromes

Syndrome	Inheritance	Key Features
Romano-Ward Syndrome	Autosomal dominant	Pure cardiac phenotype (no deafness)
Jervell and Lange-Nielsen Syndrome	Autosomal recessive	Sensorineural deafness + cardiac arrhythmias

Key Takeaways

Torsades de pointes is a polymorphic ventricular tachycardia with a characteristic twisting pattern on ECG.
Prolonged QT interval is the primary risk factor, caused by drugs, electrolyte imbalances, or congenital conditions.
Magnesium sulfate is the first-line treatment.
Congenital long QT syndromes can be inherited in autosomal dominant or recessive patterns, with some associated with sensorineural deafness.

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