torsades de pointes

Introduction

• Torsades de pointes (twisting of the points) is a characteristic form of ventricular tachycardia (VT) that displays gradual alteration in the amplitude & direction of electrical activity
• it occurs in the setting of QT prolongation.

Etiology

• congenital long QT syndromes
• end-stage cardiomyopathy
• bradycardia
• 3rd degree AV block or AV dissociation
• drug-induced prolongation of the QT interval (most common cause)
• electrolyte disturbances
  • hypokalemia
  • hypomagnesemia
• endocrine disorders
  • hypothyroidism
  • hypoparathyroidism
  • pheochromocytoma
  • hyperaldosteronism
• intracranial disorders
  • subarachnoid hemorrhage
  • stroke
  • encephalitis
  • head trauma

Epidemiology

• 70% of cases NOT associated with congenital long QT syndromes occur in women

Clinical manifestations

• intermittent & recurrent
• transient hemodynamic compromise
  • lightheadness
  • syncope or near-syncope
• complete hemodynamic collapse may occur

Diagnostic procedures

• electrocardiogram:
• prolongation of the QT interval prior to onset of torsades
• initiation of torsades is triggered by long-short sequences:
  • coupled premature ventricular complexes (PVCs)
  • ventricular bigeminy
• QRS complexes undergo gradual change in amplitude & axis

Differential diagnosis

• monomorphic ventricular tachycardia
  • due to structural heart disease, old myocardial infarction
  • intravenous amiodarone, procainamide or lidocane for hemodynamically stable patient

Management

• DC cardioversion if hemodynamically unstable
• discontinue offending agents
• MgSO4 1-2 g IV push followed by infusion of 2-20 mg/min
• increase heart rate to eliminate long-short sequence:
  • isoproterenol 2-10 ug/min
    • avoid in patients with: ischemia, severe coronary artery disease
  • temporary pacing at 80-120/min
• congenital long QT syndrome
  • beta-adrenergic receptor antagonists
• some patients may respond to:
  • lidocaine
  • phenytoin
  • bretylium
• avoid pharmacologic agents that increase the QT interval
  • class Ia & III antiarrhythmic agents

More general terms

• polymorphic ventricular tachycardia

Additional terms

• drug-induced prolongation of the QT interval
• long QT syndrome
• QT interval