Acquired long QT syndrome: as risky as congenital long QT syndrome?

Abstract

This editorial refers to ‘Role of implantable cardioverter defibrillator therapy in patients with acquired long QT syndrome: A long-term follow-up’ by G. Monnig et al ., on page 396 Long QT syndrome (LQTS) describes a group of disorders characterized by QT interval prolongation secondary to delayed cardiac repolarization that may either be genetic (otherwise known as ‘congenital’) or acquired. The substrate of abnormal cardiac repolarization predisposes to development of torsades de pointes (TdP), the characteristic form of polymorphic ventricular tachycardia, and cardiac arrest. Congenital LQTS has a population prevalence of 1 in 2000 and is caused by mutations in genes coding for cardiac ion channels and their channel interacting proteins. Delayed cardiac repolarization results mainly from loss-of-function mutations affecting rectifying potassium currents (IKs, IKr, and IK1) or gain-of-function mutations affecting the inward sodium current and rarely the L-type calcium current. Acquired LQTS has traditionally been associated with exposure to QT prolonging drugs, with antiarrhythmic medications being the most common precipitant. The main mechanism of drug-induced LQTS involves the inhibition of IKr in a similar fashion to that seen in the LQT2 subtype of congenital LQTS which arises from loss-of-function mutations in human ether-a-go-go-related gene which encodes the alpha subunit of IKr.1,2Both are associated with pause-dependent TdP. Other acute causes include electrolyte imbalance (in particular, hypokalaemia), after reversion of atrial fibrillation and transient bradyarrhythmia. There are also established chronic predisposing factors such as structural and cardiac conduction disease, metabolic and endocrine abnormalities. There is, however, a growing body of …