Congenital Long QT Syndrome: Diagnostic Criteria and Management

Definition and Epidemiology

The European Society of Cardiology defines Congenital Long QT Syndrome (LQTS) as a hereditary cardiac channelopathy characterized by prolonged ventricular repolarization, predisposing patients to life-threatening ventricular arrhythmias, particularly torsades de pointes, leading to syncope, cardiac arrest, and sudden cardiac death 1
The prevalence of LQTS is approximately 1 in 2,000 to 1 in 2,500 live births, with a mean age at presentation of 14 years, though 4% of sudden deaths occur in the first year of life 1, 2
Annual mortality in untreated patients is 0.3-0.9% for sudden cardiac death and 5% for syncope 1

The European Society of Cardiology 2015 guidelines establish diagnostic criteria, including QTc ≥480 ms on repeated ECGs, or a Schwartz score >3, which establishes clinical diagnosis 1, 6
QTc ≥500 ms is considered unequivocal LQTS regardless of family history or symptoms 1, 4
For neonates with QTc >440 ms, a comprehensive diagnostic workup is necessary, including serial 12-lead ECGs, detailed multi-generation family history, and T-wave morphology analysis 2, 3, 4

The highest risk features for sudden cardiac death include cardiac arrest survivors, QTc ≥500 ms, symptomatic patients, T-wave alternans, and 2:1 AV block secondary to QT prolongation 1, 5, 6
Genotype-specific risk varies significantly, with LQT2 females with QTc >500 ms being a particularly high-risk group 1, 5, 6

Beta-blockers are the cornerstone of treatment and must be initiated in all diagnosed patients, even if asymptomatic, with efficacy showing an 80% reduction in recurrent events in symptomatic patients 2, 3, 10
Lifestyle modifications, including avoiding QT-prolonging medications, correcting electrolyte abnormalities, restricting strenuous exercise, and avoiding genotype-specific triggers, are essential 4, 5, 10
ICD implantation is recommended in cardiac arrest survivors and patients with recurrent syncope despite adequate beta-blocker therapy 1, 6

Comprehensive family evaluation is mandatory, with all first-degree relatives requiring ECG screening and genetic counseling and testing being a Class I recommendation for probands 4, 10