Torsades de Pointes

Snapshot

• A 15-year-old girl presents with palpitations and dizziness. She has had similar episodes in the past but has never needed to go to a hospital. Her family history includes sudden cardiac death in her father and congenital sensorineural deafness in multiple family members. An echocardiogram reveals a sinusoidal waveform concerning for torsades de pointes. (Jervell and Lange-Nielsen syndrome)

Introduction

• Clinical definition
  • a polymorphic ventricular tachycardia characterized by sinusoidal and cyclic alterations on electrocardiogram (ECG)
• Epidemiology
  • demographics
    • female > male
      • women have longer QT intervals
  • risk factors 
    • hypomagnesemia
    • hypokalemia
• Etiology
  • familial
  • drugs (ABCDE)
    • class IA Antiarrhythmics (quinidine, procainamide, and disopyramide) due to ↑ QT interval
    • class III Antiarrhythmics (sotalol and ibutilide) 
    • antiBiotics 
    • antipsyChotics
    • antiDepressants
    • antiEmetics
• Pathogenesis
  • torsades de pointes is thought to result from prolonged repolarization and early afterdepolarizations
    • when early afterdepolarizations reach the threshold potential and depolarize the cell membrane, triggered activity occurs, resulting in additional action potentials
      • the triggered activity can produce torsades de pointes in susceptible patients
• Associated conditions
  • congenital long QT syndrome
    • Jervell and Lange-Nielsen syndrome 
      • autosomal recessive
      • congenital sensorineural deafness 
    • Romano-Ward syndrome 
      • autosomal dominant
      • no sensorineural deafness
• Prognosis
  • usually preceded by a period of long QT intervals
• typically resolves spontaneously, but may degenerate into ventricular fibrillation and death

Presentation

• Symptoms
  • palpitations
  • dizziness
  • syncope
  • symptoms may be triggered by stress
  • sudden cardiac death
• Physical exam
  • tachycardia
• pallor

Studies

• Labs
  • serum electrolytes (magnesium and potassium)
• Electrocardiogram (ECG) 
  • if in sinus rhythm
    • prolonged QT interval
    • pathological U waves
  • if in an episode 
    • change in polarity of QRS around the isoelectric line
    • a sinusoidal waveform 
• Making the diagnosis
• based on clinical presentation and electrocardiogram

Differential

• Supraventricular tachycardia
  • distinguishing factor
• non-sinusoidal waveforms on electrocardiogram

Treatment

• Conservative
  • discontinue all QT prolonging drugs
    • indication
      • for all patients
    • outcomes
      • torsades de pointes due to drugs typically do not recur after withdrawal of the drug
• Medical
  • magnesium sulfate
    • indications
      • for all patients
    • mechanism of action
      • suppresses early afterdepolarizations to terminate the arrhythmia
      • magnesium decreases influx of calcium and lowers the amplitude of the early afterdepolarizations
  • β-antagonists
    • indications
      • long-term therapy for patients with congenital long QT syndrome
      • only for those without bradycardia
    • drugs
      • propranolol
      • esmolol
• Operative
  • pacing
    • indication
      • long-term therapy for patients who are symptomatic despite pharmacologic treatment
• typically for patients with congenital long QT syndrome

Complications

• Ventricular fibrillation