The normal range of QT intervals in the normal population and in those with<unk>  Characteristic T-wave patterns in the 3 major subtypes of<unk> <unk>  is principally diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG).<unk>  is associated with a prolonged QTc, although in some genetically proven cases of<unk>  this prolongation can be hidden, known as concealed Long QT syndrome. The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females.<unk>  is suggested if the QTc is longer than these cutoffs. However, as 5% of normal people also fall into this category, some suggest cutoffs of 470 and 480 ms for males and females respectively, corresponding with the 99th centiles of normal values. The major subtypes of<unk>  are associated with specific ECG features. LQT1 is typically associated with broad-based T-waves, whereas the T-waves in LQT2 are notched and of lower amplitude, whilst in LQT3 the T-waves are often late onset, being preceded by a long isoelectric segment. Other factors beyond the QT interval should be taken into account when making a diagnosis, some of which have been incorporated into scoring systems such as the Schwartz score. These factors include a history of characteristic abnormal heart rhythms (Torsades de Pointes), unexplained blackouts (syncope), and a family history of confirmed LQT syndrome. Other investigations that may suggest a diagnosis of the LQT1 form of<unk>  include paradoxical lengthening of the QT interval in response to exercise (QTc >470 ms at 2–4 minutes of recovery) or during an artificial infusion of adrenaline (lengthening of the absolute QT interval >30 ms during low dose adrenaline).
Romano–Ward syndrome
Brugada syndrome
Witteveen–Kolk syndrome
Andersen–Tawil syndrome
Townes–Brocks syndrome
Laugier–Hunziker syndrome
Baggio–Yoshinari syndrome
Morgagni Stewart Morel syndrome