Long-QT syndrome and channelopathies

Overview & Definition

Picture the eight-year-old girl brought to the emergency department after collapsing during a school swimming carnival — she was pulled from the pool unconscious, briefly stiffened, and recovered fully within minutes. Her mother, who has fainted "all her life," wonders whether this was a fit. The triage label says "vasovagal or seizure — query epilepsy." That child carries the whole story of long-QT syndrome: an arrhythmic collapse triggered by exertion, mislabelled as a seizure or a faint, in a family with a heritable tendency to sudden death. One twelve-lead ECG, read for the QT interval, would have changed everything. [1] [2]

Long-QT syndrome is the commonest inherited cardiac arrhythmia syndrome, with a prevalence of about one in two thousand individuals. It is defined by prolongation of the corrected QT interval on the surface electrocardiogram, reflecting delayed repolarisation of the ventricular myocardium. The delayed repolarisation creates a vulnerable window in which early afterdepolarisations can arise, triggering the characteristic polymorphic ventricular tachycardia known as torsades de pointes, which may terminate spontaneously as a faint or progress to ventricular fibrillation and sudden cardiac death. [2] [10]

The clinical importance of LQTS rests on three facts. It is treatable: beta-blockers reduce events by roughly two-thirds and more aggressive therapy is available for the high-risk subset. It is under-diagnosed: syncope during exertion or emotion is routinely mislabelled as vasovagal or epileptic, and the first presentation in a family is sometimes the proband's sudden death. And it is heritable in an autosomal dominant pattern, so a diagnosis in one person carries implications for first-degree relatives who may be asymptomatic but at risk. [1] [6]