7 Mutations in proteins associated with ion channels but not part of the channels themselves can also cause LQTS. LQTS affects an estimated 1 in 2500 people 4 and is understood to be a collection of genetically distinct arrhythmogenic disorders resulting from genetic mutations in (primarily) cardiac potassium and sodium ion channels, termed “cardiac channelopathies”. 4 Torsades de pointes can precipitate syncope, seizures or sudden death, depending on whether the heart rhythm spontaneously reverts to normal rhythm or if the patient is defibrillated to normal rhythm before death occurs. 1– 3 The trademark event for the symptomatic LQTS patient is the potentially lethal ventricular dysrhythmia called torsades de pointes. The current guideline recommendations for the athlete with LQTS are also summarised.Ĭongenital long QT syndrome (LQTS) was first described clinically as Jervell and Lange-Nielsen syndrome and Romano Ward syndrome in the late 1950s and early 1960s. This review discusses the components of accurate QTc measurement and diagnosis, re-examines what is known about factors affecting QT interval measurement, and clarifies current recommendations regarding diagnosis of so-called “borderline” QT interval prolongation. However, the 12-lead ECG remains the universal initial diagnostic test in the evaluation of LQTS and is subject to miscalculation, misinterpretation and mishandling. Indeed, genetic testing exerts significant diagnostic, prognostic and therapeutic implications.
Although a normal QT interval imparts a much lower risk of life-threatening events, it does not preclude a patient from nevertheless harbouring a potentially lethal LQTS-causing genetic mutation. Whereas someone exhibiting marked prolongation of the QT interval with QTc exceeding 500 ms who was just externally defibrillated from torsades de pointes while swimming poses negligible diagnostic challenge as to the unequivocal probability of LQTS, the certainty is considerably less for the otherwise asymptomatic person who happens to host a QTc value coined “borderline” (QTc ≥440 ms). Congenital long QT syndrome (LQTS) affects an estimated 1 in 2500 people and typically presents with syncope, seizures or sudden death.
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