Statistics

Cutoff

Physics

Clinical psychology

QT interval

Cardiology

Quantum mechanics

Mathematics

Percentile

Internal medicine

Psychometrics

Long QT syndrome

Medicine

Cohort

Intraclass correlation

Confidence interval

Circulation

Background: Long QT syndrome (LQTS) is associated with potentially fatal arrhythmias. Treatment is very effective, but its diagnosis may be challenging. Importantly, different methods are used to assess the QT interval, which makes its recognition difficult. QT experts advocate manual measurements with the tangent or threshold method. However, differences between these methods and their performance in LQTS diagnosis have not been established. We aimed to assess similarities and differences between these 2 methods for QT interval analysis to aid in accurate QT assessment for LQTS. Methods: Patients with a confirmed pathogenic variant in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3) genes and their family members were included. Genotype-positive patients were identified as LQTS cases and genotype-negative family members as controls. ECGs were analyzed with both methods, providing inter- and intrareader validity and diagnostic accuracy. Cutoff values based on control population’s 95th and 99th percentiles, and LQT...

Determination and Interpretation of the QT Interval