Long QT syndrome

To the Editor: Levine and colleagues have done an excellent review of congenital long QT syndrome.¹ I would like to emphasize that there are significant differences in risk between children and adults with long QT syndrome. According to a recent registry study,^2,3 the following are salient differences.

In children²:

• A prolonged corrected QT interval (QTc) (ie, > 500 ms) seems to predict risk of sudden cardiac death in boys.
• Syncope predicts aborted cardiac arrest or sudden cardiac death in both boys and girls, with recent syncope carrying a higher risk than a remote history of syncope.
• Although 63% of the sample in the registry consisted of girls, who also had longer baseline QTc intervals than boys, only 1% of girls had events, compared with 5% of boys.
• Family history of sudden cardiac death does not predict risk of cardiac events during childhood regardless of genotype.

In adults³:

• Event rates were similar regardless of QTc interval in men, whereas women with longer QTc intervals had more events than those without significantly prolonged QTc intervals.
• Recent syncope carries a tenfold increased hazard ratio for serious adverse events.
• A prolonged QTc interval predicts a substantial risk of aborted cardiac arrest or sudden cardiac death in people older than 40 years.
• The combination of a family history of sudden cardiac death and the LQT3 (long QT syndrome type 3) mutation carries a significant mortality rate.