Elsevier

The Lancet

Volume 354, Issue 9190, 6 November 1999, Pages 1625-1633
The Lancet

Seminar
Long QT syndromes and torsade de pointes

https://doi.org/10.1016/S0140-6736(99)02107-8Get rights and content

Summary

In the long QT syndromes (LQTS), malfunction of ion channels impairs ventricular repolarisation and triggers a characteristic ventricular-tachyarrhythmia: torsade de pointes. Symptoms in the LQTS (syncope or cardiac arrest) are caused by this arrhythmia. In congenital LQTS, mutations in the genes encoding for ion chanels cause this channel malfunction. Six genotypes (LQT1 to LQT6) have been identified, and attempts are being made to correlate different mutations with clinical signs and specific therapy. In acquired LQTS, channel malfunction is caused by metabolic abnormalities or drugs. The list of drugs that may impair ion-channel function expands continuously. Moreover, attributes that increase the risk for drug-induced torsade (eg, female sex, recent heart-rate slowing, or hypokalaemia) and electrocardiographic “warning signs” are recognised. Recent data suggest that patients with an acquired LQTS have some underlying predisposition to proarrhythmia. Mutations causing “silent” forms of congenital LQTS, in which the patient remains free of arrhythmias until exposed to drugs that further impair repolarisation, are now recognised.

Section snippets

Acute identification of torsade de pointes

Two electrocardiographic features of torsade de pointes that help to establish a diagnosis are its typical mode of onset and its morphology.

Almost all arrhythmias caused by an acquired LQTS,24, 25 and most arrhythmias caused by congenital LQTS (at least in adults),26, 27 are preceded by pauses (figure 2). The pauses that lead to torsade de pointes may be due to sinus arrhythmia or sinus arrest. More commonly, these are “post-extrasystolic pauses”24, 25, 26 (figure 2). In a typical escalating

Emergency therapy for torsade de pointes

Torsade de pointes that degenerates to ventricular fibrillation requires DC shock for termination. However, torsade de pointes is not sustained in most cases, and even prolonged arrhythmias may terminate spontaneously. Since the stress caused by DC shocks may trigger recurrent arrhythmias, shock delivery should be withheld until the patient loses consciousness or is sedated. More challenging is the prevention of immediate recurrence of torsade de pointes. Urgent measures include: removal of any

Long-term management of congenital LQTS

Two forms of familial LQTS have long been known: the Jervell and Lange-Nielsen syndrome (with congenital deafness and malignant arrhythmias in infancy); and the Romano-Ward syndrome (with normal hearing and autosomal-dominant inheritance). The first form is very rare. Hence, gene mutations were first identified for families with normal hearing. In the Jervell-Lange-Nielsen syndrome the cardiac malfunction (involving IKs channels) is of autosomal-dominant inheritance, whereas deafness is

Bradyarrhythmia-induced torsade de pointes

The slower the heart rate, the longer the repolarisation will be. Even short-lasting bradycardia, such as that caused by adenosine injection, may rarely culminate in torsade de pointes.49 However, bradyarrhythmia-induced torsade de pointes is primarily seen during complete atrioventricular block. Additional risk factors (panel 3) increase the risk of torsade de pointes during bradyarrhythmias. Hypokalaemia must be prevented in patients with bradyarrhythmias. Nevertheless, the most important

Is acquired LQTS really “acquired”?

Several lines of evidence suggest that patients with acquired LQTS have some underlying predisposition to proarrhythmia. The QT measured before drug exposure tends to be longer in patients who eventually develop drug-induced torsade de pointes than in patients who receive the same drug safely.20, 21, 70 Patients with drug-induced torsade de pointes are at high risk of recurrent arrhythmias if exposed to a second antiarrhythmic drug.21 Among patients with heart block, the QT interval (rather

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