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Acquired long QT syndrome

Authors
Charles I Berul, MD
Stephen P Seslar, MD, PhD
Peter J Zimetbaum, MD
Section Editors
John K Triedman, MD
Samuel Lévy, MD
Samuel Asirvatham, MD
Deputy Editor
Brian C Downey, MD, FACC

INTRODUCTION

The long QT syndrome (LQTS) is a disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram (ECG) (waveform 1) [1-3]. This syndrome is associated with an increased risk of a characteristic life-threatening cardiac arrhythmia, known as torsades de pointes (TdP) (waveform 2A-B) [4,5]. The primary symptoms in patients with LQTS include palpitations, syncope, seizures, and sudden cardiac death (SCD).

The long QT syndrome may be either genetic or acquired [6-9]. Acquired LQTS usually results from drug therapy, hypokalemia, or hypomagnesemia (table 1). As will be described below, hypokalemia, hypomagnesemia, and bradycardia can increase the risk of drug-induced LQTS. In addition, some patients with acquired LQTS have an underlying "forme fruste" of congenital LQTS. (See 'Mutations in LQTS genes' below.)

The pathophysiology, causes, and management of acquired LQTS will be reviewed here. The clinical manifestations of acquired LQTS are similar to those in congenital disease and are discussed elsewhere. (See "Clinical features of congenital long QT syndrome".)

NORMAL QT INTERVAL

The normal range for the rate-corrected QT interval is similar in males and females from birth until late adolescence (0.37 to 0.44 sec). In adults, females have slightly longer QT intervals than males. A corrected QT interval of more than 0.45 sec is considered prolonged in men; the normal range generally is extended to 0.45 to 0.47 seconds in women (table 2) [10]. (See 'Diagnosis' below.)

TORSADES DE POINTES

Torsades de pointes (TdP) is a form of polymorphic ventricular tachycardia (VT) that occurs in the setting of acquired or congenital QT interval prolongation [4,5]. Polymorphic VT is defined as a ventricular rhythm faster than 100 beats per min with frequent variations of the QRS axis, morphology, or both [5,6]. In the specific case of TdP, these variations take the form of a progressive, sinusoidal, cyclic alteration of the QRS axis (waveform 2A-B). The peaks of the QRS complexes appear to "twist" around the isoelectric line of the recording; hence the name torsades de pointes or "twisting of the points".

                         

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Literature review current through: Nov 2016. | This topic last updated: Tue May 05 00:00:00 GMT 2015.
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