Measurement of the<unk>  interval with normal and prolonged<unk>  intervals left Diagnosing<unk>  is challenging. Whilst the hallmark of<unk>  is prolongation of the<unk>  interval, the<unk>  interval is highly variable among both those who are healthy and those who have<unk> . This leads to overlap between the<unk>  intervals of those with and without<unk> . 2.5% of those with genetically proven<unk>  have a<unk>  interval within the normal range. Conversely, given the normal distribution of<unk>  intervals, a proportion of healthy people will have a<unk> er<unk>  interval than any arbitrary cutoff. Other factors beyond the<unk>  interval should therefore be taken into account when making a diagnosis, some of which have been incorporated into scoring systems. Electrocardiogram Characteristic ECG patterns associated with the three major subtypes of inherited<unk> <unk>  is principally diagnosed by measuring the<unk>  interval corrected for heart rate <unk> c) on a 12-lead electrocardiogram (ECG).<unk>  is associated with a prolonged<unk> c, although in some genetically proven cases of<unk>  this prolongation can be hidden, known as concealed<unk> . The<unk> c 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<unk> c is<unk> er 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 inherited<unk>  are associated with specific ECG features.<unk> 1 is typically associated with broad-based T-waves, whereas the T-waves in<unk> 2 are notched and of lower amplitude, whilst in<unk> 3 the T-waves are often late onset, being preceded by a<unk>  isoelectric segment. Schwartz score T-wave alternans in an individual with<unk>  The Schwartz score has been proposed as a method of combining clinical and ECG factors to assess how likely an individual is to have an inherited form of<unk> . The table below lists the criteria used to calculate the score. + Schwartz score to aid diagnosis of inherited<unk> . Corrected<unk>  interval <unk> c) ≥ 480 ms 3 points<unk> c defined according to Bazett's correction 460–470 ms 2 points 450 ms and male gender 1 point Torsades de pointes 2 points T-wave alternans 1 point Notched T-waves in at least 3 leads 1 point Low heart rate for age (children) 0.5 points Syncope with stress 2 points Cannot receive points both for syncope and Torsades without stress 1 point Congenital deafness 0.5 points Family history Other family member with confirmed<unk>  1 point Same family member cannot be counted for<unk>  and sudden death Sudden cardiac death in immediate family member aged <30 0.5 point Score: 0–1 : low probability of<unk> ; 2–3 : intermediate probability of<unk> ; ≥ 4 : high probability of<unk>  Other investigations In cases of diagnostic uncertainty, other investigations may be helpful to unmask a prolonged<unk> . In addition to prolonging the resting<unk>  interval,<unk>  may affect how the<unk>  changes in response to exercise and stimulation by catecholamines such as adrenaline. Provocation tests, in the form of exercise tolerance tests or direct infusion of adrenaline, can be used to detect these abnormal responses. These investigations are most useful for identifying those with concealed congenital Type 1<unk>  1 <unk> 1) who have a normal<unk>  interval at rest. While in healthy persons the<unk>  interval shortens during exercise, in those with concealed<unk> 1 exercise or adrenaline infusion may lead to paradoxical prolongation of the<unk>  interval, revealing the underlying condition. Guideline cutoffs International consensus guidelines differ on the degree of<unk>  prolongation required to diagnose<unk> . The European Society of Cardiology recommends that, with or without symptoms or other investigations,<unk>  can be diagnosed if the corrected<unk>  interval is<unk> er than 480ms. They recommend that a diagnosis can be considered in the presence of a<unk> c of greater than 460 ms if unexplained syncope has occurred. The Heart Rhythm Society guidelines are more stringent, recommending<unk> c cutoff of greater than 500 ms in the absence of other factors that prolong the<unk> , or greater than 480 ms with syncope. Both sets of guidelines agree that<unk>  can also be diagnosed if an individual has a Schwartz score of greater than 3 or if a pathogenic genetic variant associated with<unk>  is identified, regardless of<unk>  interval.
Long QT syndrome
Brugada syndrome
Short QT syndrome
Arrhythmogenic cardiomyopathy
Catecholaminergic polymorphic ventricular tachycardia
Opitz G/BBB syndrome
Jervell and Lange-Nielsen syndrome
Familial atrial fibrillation