13th March 2024

Pathophysiology

Long QT syndrome (LQTS) can be congenital or acquired and is characterised by a prolonged QT interval on electrocardiogram (ECG) as a result of prolonged ventricular repolarisation. 

The QT interval on an ECG can be adjusted to estimate the QT interval at a heart rate of 60 beats per minute; this is known as the corrected QT (QTc) and is used to measure QT length. QTc is prolonged if > 440 ms in men or > 460ms in women.

Acquired LQTS can be due to medications or electrolyte abnormalities as well as due to forms of bradyarrhythmia. However, the focus of this section is on congenital LQTS.

Congenital LQTS occurs in around 1 in 2000 people worldwide and results from genetic mutations coding for ion channels responsible for prolonging myocardial repolarisation, which in turn prolongs QT interval. A prolonged QT interval or corrected QT (QTc) can result in arrhythmias, most commonly a form of polymorphic ventricular tachycardia called torsades de pointes. Although multiple genes have been identified in congenital LQTS, three genes account for as many as 80-95% of cases, which are shown below.