Tuesday, September 9, 2008

What is Torsades de Pointes?

Torsades de pointes, or simply torsades is a French term that literally means "twisting of the points". It was first described by Dessertenne in 1966 and refers to a specific variety of ventricular tachycardia that exhibits distinct characteristics on the electrocardiogram (ECG).

Torsade de pointes is a distinctive polymorphic ventricular tachycardia in which the QRS amplitude varies and the QRS complexes appear to twist around the baseline. Torsade de pointes is associated with a prolonged QT interval, which may be congenital or acquired. It is usually not sustained and terminates spontaneously but frequently recurs unless the underlying cause is corrected and may degenerate into sustained ventricular tachycardia or ventricular fibrillation. Torsade is a life-threatening arrhythmia and may present as sudden cardiac death in patients with structurally normal hearts.

  • The corrected QT interval is longer in the white population than in the black population, and longer in females than males. Therefore torsade de pointes is more common in white races and in females.
  • Torsade occurs at any age. If it occurs at an early age, the cause is usually due to congenital long QT syndrome. In later years, the cause is usually due to acquired long QT syndrome.

Risk factors

  • Episodes of torsade in patients with congenital long QT syndromes may be triggered by stress, fear or physical exertion.
  • Patients with torsade usually present with recurrent episodes of palpitations, dizziness, and syncope. Sudden cardiac death can occur with the first episode.
  • Nausea, pallor, cold sweats, shortness of breath and chest pain also may occur.
  • Physical findings depend on the rate and duration of tachycardia and the degree of cerebral hypoperfusion. Findings include rapid pulse, low or normal blood pressure or transient or prolonged loss of consciousness.
  • Other physical signs depend on the cause of torsade, e.g. features of a congenital disorder.
Differential diagnosis
  • Polymorphic ventricular tachycardia
  • Monomorphic ventricular tachycardia
  • Supraventricular tachycardia with aberrant conduction
  • Other causes of syncope or sudden cardiac death
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  • ECG:
    • Paroxysms of 5-20 beats, with a heart rate faster than 200 beats per minute. Sustained episodes are occasionally seen.
    • Progressive change in polarity of QRS about the isoelectric line occurs with complete 180 degree twist of QRS complexes in 10-12 beats.
    • Usually, a prolonged QT interval and pathological U waves are present, reflecting abnormal ventricular repolarisation. The most consistent indicator of QT prolongation is a QT of 0.60 s or longer or a QTc (corrected for heart rate) of 0.45 s or longer.
    • A short-long-short sequence between the R-R interval occurs before the trigger response.
  • Electrolytes; hypokalaemia, hypomagnesaemia and hypocalcaemia.
  • Cardiac enzymes; rule out myocardial ischaemia.
  • Chest x-ray and echocardiography; rule out structural heart disease if any clinical suggestion is present.

Short-term treatment

  • Resuscitation
  • Defibrillation:
    • Although torsade frequently is self-terminating, it may degenerate into ventricular fibrillation, which requires defibrillation.
    • In an otherwise stable patient, DC cardioversion is kept as a last resort because torsade is paroxysmal in nature and frequently recurs after cardioversion.
  • Discontinuation of any offending agent and correction of any underlying cause such as hypokalaemia, hypomagnesaemia and bradycardia.
  • Suppression of early after depolarisations:
    • Intravenous magnesium is the drug of choice for torsades de pointes. Magnesium is effective even in patients with normal magnesium levels.
    • Acceleration of the heart rate can be achieved by using beta 1-adrenergic agonists such as isoproterenol or overdrive electrical pacing.
    • Isoproterenol is used as an interim treatment until overdrive pacing can be started:
      • Can be used in bradycardia-dependent torsade that is usually associated with acquired long QT syndrome. It is given as a continuous IV infusion to keep the heart rate faster than 90 beats per minute.
      • Isoproterenol accelerates AV conduction and decreases the QT interval by increasing the heart rate and reducing temporal dispersion of repolarisation.
      • Beta-adrenergic agonists are contraindicated in the congenital form of long QT syndrome.
    • Temporary transvenous pacing:
      • Pacing can be effective in terminating torsade by increasing the heart rate and so reducing the QT interval.
      • Atrial pacing is the preferred mode because it preserves the atrial contribution to ventricular filling. In patients with AV block, ventricular pacing can be used to suppress torsade.

Long-term treatment

  • Patients without syncope, ventricular tachyarrhythmia or a family history of sudden cardiac death can be observed without starting any treatment.
  • Congenital long QT syndrome:
    • Beta-adrenergic antagonists are used as a first-line long-term therapy in congenital long QT syndrome. Propranolol is has been the most extensively used.
    • Beta-blockers are contraindicated in acquired cases because bradycardia produced by these agents can precipitate torsade. They should also be avoided in those congenital cases in which bradycardia is a prominent feature.
    • Permanent pacing benefits patients who remain symptomatic despite receiving the maximally tolerated dose of beta-blockers and can be used in addition to beta-blockers.
    • High left thoracic sympathectomy is effective in patients who remain refractory to beta-blockade and pacing.
    • Implantable cardioverter-defibrillators (ICDs) are useful in rare instances when torsade still continues despite all of these treatments. Beta-blockers should be used along with ICDs because shock can further precipitate torsade by adrenergic stimulation.
  • Acquired long QT syndrome:
    • Long-term treatment in acquired cases is usually not required because the QT interval returns to normal once the predisposing factor has been corrected.
    • Pacemaker implantation is effective in cases that are associated with heart block or bradycardia.
    • Implantable cardioverter-defibrillators are indicated in cases that cannot be managed by avoidance of any specific precipitating factor.
  • Monomorphic ventricular tachycardia
  • Ventricular fibrillation
  • Sudden cardiac death
  • Patients may revert spontaneously or convert to a non-polymorphic ventricular tachycardia or ventricular fibrillation.
  • Torsade is a life-threatening arrhythmia and may present as sudden cardiac death in patients with structurally normal hearts. In congenital long QT syndrome, the mortality rate for untreated patients is 50% in 10 years, which can be reduced to 3-4% with treatment.
  • In acquired long QT syndrome, the prognosis is excellent once any precipitating factor has been removed.
  • Avoid offending drugs that prolong the QT interval.
  • Prevent predisposing conditions such as hypokalaemia, hypomagnesaemia, and hypocalcaemia, especially in patients shown to have long QT interval.
  • Screen families of patients with torsade for whom the cause for prolonged QT is suggested to be congenital.