Torsades de pointes overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Torsade de pointes, in French means "Twisting of the Points". It is characterized by a polymorphic ventricular tachycardia and can occur in the congenital long QT syndromes, electrolyte abnormalities (hypomagnesemia, hypokalemia), usage of certain drugs like antiarrhythmic (quinidine), nonsedating antihistamines (terfenadine); antibiotics (erythromycin) and neuroleptics (thioridazine).
Historical Perspective
The term "torsade de pointes" was first described by Dessertenne in 1966, based on the characteristic "twisting" pattern of ventricular tachycardia seen on EKG.
Pathophysiology
Torsade de pointes is characterized by constantly changing rhythm amplitude. The changing rhythm amplitudes comes from the ventricular depolarizing waves constantly shifting its axis. The underlying mechanism is thought to be triggered activity arising as a consequence of early after-depolarizations. Torsade de pointes is typically initiated by a short-long-short interval. A ventricular extrasystole (first beat: short) is followed by a compensatory pause. The following beat (second beat: long) has a longer QT interval. If the next beat follows shortly thereafter, there is a good chance that this third beat falls within the QT interval, resulting in the R on T phenomenon and subsequent Torsade de pointes. During Torsade de pointes the ventricles depolarize in a circular fashion resulting in QRS complexes with a continuously turning heart axis around the baseline (hence the name Torsade de Pointes).
Causes
Common causes for torsades de pointes include hypomagnesemia and hypokalemia. It is commonly seen in malnourished individuals and chronic alcoholics. Drug interactions such as erythromycin or Avelox, taken concomitantly with inhibitors like nitroimidazole, diarrhea, dietary supplements, and various medications like methadone, lithium, tricyclic antidepressants or phenothiazines may also contribute to causing torsades de pointes.
Risk Factors
Long QT syndrome is a risk factor for developing torsades de pointes, and can either be inherited as congenital mutations of ion channels carrying the cardiac impulse/action potential, or acquired as a result of drugs that block these cardiac ion currents. Other risk factors include electrolyte abnormalities, heart failure, left ventricular hypertrophy, female gender or renal and liver failure. Being on certain medications also pose a risk for developing torsades de pointes.
Natural History, Complications and Prognosis
Although Torsades de Pointes (TdP) is a rare ventricular arrhythmia, it can degenerate into ventricular fibrillation, leading to death without rapid medical intervention.
Treatment
An understanding of the pathophysiology has led to development of treatment modalities like pacing, isoproterenol and drugs like magnesium and beta blockers.