Guidelines for the diagnosis and management of familial long QT syndrome.

1.1 Definition and prevalence Long QT syndrome (LQTS) is a familial condition causing syncope and sudden death through rapid ventricular tachycardia (torsade de pointes), which can deteriorate to ventricular fibrillation, in otherwise fit and healthy young people. Prevalence is approximately 1 in 2,500. 1 Clinical diagnosis is made from a combination of suspicious history, family history and the twelve lead ECG, which typically reveals a heart-rate corrected QT interval (QT//R-R interval=QTc) of greater than 0.46 in women and 0.45 in men. QT interval behaviour after exercise testing is often helpful in making the diagnosis.