Torsades de pointes

Background

• Form of polymorphic VTach
  • Gradual change in the amplitude of QRS complexes and twisting around isoelectric line
• Associated with congenital or acquired prolonged QT

Common Causes

POINTES mnemonic:

• Phenothiazines
• Other medications (ie TCAs)
• Intracranial bleed
• No known cause (idiopathic)
• Type I anti-arrhythmics (quinidine, procainamide, disopyramide)
• Electrolyte abnormalities (hypoK & hypoMag)
• Syndrome of Prolonged QT (aka Long QT Syndrome)

Clinical Features

• Syncope
• Dizziness
• Lightheadedness
• Palpitations
• Sudden Cardiac Death

Evaluation

Workup

• ECG
• BMP, Mg, Phos

Diagnosis

Classic torsades in 12-lead

Torsades de Pointes (TdP) in patient with a potassium of 2.4 mmol/L and a magnesium of 1.6mg/dL.

• ECG in which the QRS complexes “twist” around the isoelectric line

Differential Diagnosis

• Drug induced
• Congenital long QT
• Hypocalcemia
• Hypomagnesemia
• Hypokalemia
• Hypothermia
• POINTES as above

Management

Increasing HR decreases QT interval

1. Magnesium sulfate - decreases calcium influx
   • 1-2gm IV over 1-2 min, repeat in 5-15min; then 1-2gm/hr (3-10mg/min) drip
     • Danger of hypermagnesemia → depressed neuromuscular function and respiratory drive, so monitor closely
     • Supplement with K+
2. Isoproterenol - Increases HR / AV conduction
   • 2-8 mcg/min
   • Target HR > 90 bpm
3. Overdrive Pacing - Atrial > Ventricular pacing
   • Goal HR 90-120
   • Note: Not a treatment for TdP, but useful in maintaining sinus rhythm
4. Defibrillation / synchronized cardioversion - Patient in extremis
5. AVOID amiodarone and procainamide, which may worsen prolonged QT
6. Lidocaine (a class Ib antiarrhythmic drug) shortens the QT interval and may be effective especially for drug-induced torsades de pointes.

See Also

• Tachycardia (Wide)
• ACLS (2010 Guidelines)