Epidemiology

Historically, only the most severe cases of LQTS were detected and reported, suggesting that the condition was extremely rare.[9] However, it is currently estimated that at least 1 in 2000 to 1 in 2500 people worldwide are affected with congenital LQTS, although its observed prevalence has increased as awareness and screening for the condition has improved.[4][5][11]​​​​​​ Untreated LQTS has an annual rate of sudden cardiac death of <0.5% in asymptomatic patients, which rises to approximately 5% in patients who have a history of syncope.[2] LQTS is thought to be responsible for approximately 3000 sudden deaths in the US annually.[11][12][13][14]​​​​​ The 10-year mortality rate in untreated, symptomatic index cases is approximately 50%.[5]

The mean age of patients at presentation is 14 years.[2]​ Few data are available to suggest worldwide racial or ethnic variation in prevalence, but this has not been widely studied. LQTS is more commonly diagnosed in women, which may be a spurious observation resulting from the higher upper limit for the corrected QT interval (QTc) in postpubertal females than in males (460 ms and 450 ms, respectively), although one report suggests a slightly higher incidence in women on the basis of genetics.[15] About 70% to 85% of patients with LQTS have an identifiable genetic mutation.[2][5]​​ The LQT1, LQT2, and LQT3 subtypes of the condition constitute over 90% of cases for which a gene can be identified, with LQT4 to LQT15 accounting for the remainder. KCNQ1 mutations, which lead to LQT1, account for up to 35% to 45% of genotyped patients and are the most commonly identified mutations in these patients, followed by KCNH2 mutations, which lead to LQT2.[16] Romano-Ward syndrome is the most common form of LQTS and has an autosomal dominant form of inheritance, as opposed to the Jervell and Lange-Nielsen syndrome, which is a rare autosomal recessive form of LQTS.[8]

The overall incidence and prevalence of acquired LQTS is not known and is difficult to estimate. In one retrospective review of hospital admissions, 0.7% of patients had a corrected QT interval >500 ms.[17] In another case-control study from a cohort of hospitalised cancer patients, 1.5% had a corrected QT interval >500 ms.[18]

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