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.

Can be associated with CAV3 mutation

Causes of a prolonged QT interval:

• 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

• may be picked up on routine ECG or following family screening
• Long QT1 - usually associated with exertional syncope, often swimming
• Long QT2 - often associated with syncope occurring following emotional stress, exercise or auditory stimuli
• Long QT3 - events often occur at night or at rest
• sudden cardiac death

Management

• avoid drugs which prolong the QT interval and other precipitants if appropriate (e.g. Strenuous exercise)
• beta-blockers
• implantable cardioverter defibrillators in high risk cases

^ 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