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 which may be secondary to medications

Common Causes

POINTES mnemonic:

• Phenothiazines
• Other medications (ie TCAs)
• Intracranial bleed
• No known cause (idiopathic)
• Type I antiarrhythmics (quinidine, procainamide, disopyramide)
• Electrolyte abnormalities (hypoK & hypoMg)
• Syndrome of Prolonged QT (aka Long QT Syndrome)
• Other causes:
  • Organophosphate toxicity
  • Hydrocarbon toxicity
  • Chloral hydrate toxicity
  • Hypothermia

Clinical Features

• Syncope
• Dizziness, lightheadedness
• Palpitations
• Sudden cardiac arrest

Differential Diagnosis

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

Wide-complex tachycardia

Assume any wide-complex tachycardia is ventricular tachycardia until proven otherwise (it is safer to incorrectly assume a ventricular dysrhythmia than supraventricular tachycardia with abberancy)

• Regular
  • Monomorphic ventricular tachycardia
  • PSVT with aberrant conduction:
    • PSVT with bundle branch block^
    • PSVT with accessory pathway
    • Atrial flutter with bundle branch block^
  • Sinus tachycardia with bundle branch block^
  • Accelerated idioventricular rhythm (consider if less than or ~120 bpm)
  • Metabolic
    • Hyperkalemia
    • Digoxin toxicity
    • Severe metabolic acidosis
• Irregular
  • Atrial fibrillation/atrial flutter with variable AV conduction AND bundle branch block^
  • Atrial fibrillation/atrial flutter with variable AV conduction AND accessory pathway (e.g. WPW)
  • Atrial fibrillation + hyperkalemia
  • Polymorphic ventricular tachycardia
    • Torsades de pointes
    • Nonsustained ventricular tachycardia

^Fixed or rate-related

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 showing the QRS complexes “twisting” around the isoelectric line

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
   • Lidocaine 1 mg/kg bolus, followed by 0.5-4 mg/min, titrated to rhythm response
   • Inpatient may monitor plasma lidocaine levels, with goal < 6 mcg/mL

Disposition

• Admit

See Also

• Tachycardia (Wide)
• ACLS (2010 Guidelines)
• In-Training Exam Review