Long QT syndrome (LQTS) is an inherited condition associated with delayed repolarization of the ventricles. It is important to recognise as it may lead to ventricular tachycardia/torsade de pointes and can therefore cause collapse/sudden death. The most common variants of LQTS (LQT1 & LQT2) are caused by defects in the alpha subunit of the slow delayed rectifier potassium channel. A normal corrected QT interval is less than 430 ms in males and 450 ms in females.
Causes of a prolonged QT interval:
| Congenital | Drugs* | Other |
|---|---|---|
| • Jervell-Lange-Nielsen syndrome (includes deafness and is due to an abnormal potassium channel) | ||
| • Romano-Ward syndrome (no deafness) | amiodarone, sotalol, class 1a antiarrhythmic drugs | |
| tricyclic antidepressants, | ||
| SSRIs (especially citalopram) | ||
| methadone | ||
| chloroquine | ||
| terfenadine^^ | ||
| erythromycin | ||
| haloperidol | ||
| Anti-emetics: ondanestron, metoclopramide, domperidone | Malnutrition & electrolyte imbalance: hypocalcaemia, hypokalaemia, hypomagnesaemia | |
| acute myocardial infarction | ||
| myocarditis | ||
| hypothermia | ||
| CNS: subarachnoid haemorrhage, ischaemic stroke |
Features
Management
^ the usual mechanism by which drugs prolong the QT interval is blockage of potassium channels. See the link for more details
^^ a non-sedating antihistamine and classic cause of prolonged QT in a patient, especially if also taking P450 enzyme inhibitor, e.g. Patient with a cold takes terfenadine and erythromycin at the same time
^^^ note sotalol may exacerbate long QT syndrome