Long QT syndrome

Definition

An inherited disorder of ventricular repolarization marked by abnormal prolongation of the heart-rate-corrected QT interval (QTc). Under the 2022 ESC guideline it is diagnosed at a QTc of 480 ms or more on repeated 12-lead ECGs or with an LQTS (Schwartz) diagnostic score above 3, and it is considered at a QTc of 460 to 479 ms in a patient with arrhythmic syncope when no secondary cause of QT prolongation is present; the 2013 HRS/EHRA/APHRS consensus used a QTc of 500 ms or more, or 480 to 499 ms with unexplained syncope, in each case in the absence of a secondary cause. Over 92 percent of genetically confirmed cases involve KCNQ1 (LQT1), KCNH2 (LQT2) or SCN5A (LQT3), ion-channel genes whose variants prolong repolarization. Prolonged repolarization allows early afterdepolarizations, which can trigger polymorphic ventricular tachycardia of the torsades de pointes type.

Clinical noteA high Schwartz risk score or an unequivocal pathogenic mutation can establish the diagnosis even when the QTc is not markedly prolonged.