Congenital Long QT Syndrome Type 2: Delayed Diagnosis After a Decade of Seizure-Like Episodes.

BACKGROUND

Congenital long QT syndrome (LQTS) is typically diagnosed in youth. Recognition in advanced age is rare and may be delayed when arrhythmic syncope mimics epilepsy.

CASE SUMMARY: A 93-year-old man with recurrent convulsive syncope presented with marked QT prolongation, notched T waves, and pause-dependent torsades de pointes/pulseless ventricular tachycardia initiated by premature ventricular contractions. Four years earlier, torsades de pointes had been attributed to mild hypokalemia and famotidine, although QTc interval remained prolonged after correction. Genetic testing identified a pathogenic KCNH2 frameshift variant, confirming congenital LQTS type 2. Advanced age, chronic kidney disease, and bradyarrhythmia likely reduced repolarization reserve. An implantable cardioverter-defibrillator was discussed but not pursued after a goals-of-care discussion; leadless pacing was used to reduce pauses, and beta-blocker therapy continued.

DISCUSSION: Congenital LQTS may remain occult into advanced age when acquired factors reduce repolarization reserve.

TAKE-HOME MESSAGE: Persistent QT prolongation after reversible factors are corrected should prompt consideration of congenital LQTS regardless of age.