Daytime benign, nocturnal lethal: Diagnostic challenges and fatal delays in phenotypic type 3 long QT syndrome: A case report

Background: Congenital long QT syndrome (LQTS) is an inherited channelopathy that predisposes to torsade de pointes (TdP) and sudden cardiac death (SCD). Arrhythmic syncope is frequently misattributed to vasovagal or psychogenic causes, and this misdiagnosis delays appropriate management. In high-risk patients, implantable cardioverter-defibrillator (ICD) implantation provides the most effective protection against fatal nocturnal arrhythmic events. Case Presentations: A previously healthy 17-year-old female was referred after one year of recurrent nocturnal syncope, which two previous clinicians had attributed to a psychogenic cause. The episodes occurred only during sleep and were preceded by palpitations; there were no auditory or emotional triggers. Family history, physical examination, serum electrolytes, and echocardiography were unremarkable. The electrocardiogram showed sinus arrhythmia, prolonged ST segments, late-onset and bifid T waves, and a QTc of 520 to 583 ms. Tilt-table testing was negative. Holter monitoring during sleep captured self-terminating polymorphic ventricular tachycardia with torsade de pointes morphology. A modified Schwartz score of 7.5 indicated a high probability of congenital LQTS, consistent with the LQT3 phenotype. Beta-blocker therapy was initiated, and ICD implantation was scheduled; genetic testing and mexiletine were not available. At the family's request, the procedure was postponed completing a national university examination. Before the rescheduled implantation, she developed nocturnal palpitations, lost consciousness, and died. Conclusions: Nocturnal syncope in adolescents requires thorough assessment of the QT interval and T-wave morphology. Once high-risk LQTS is established, ICD implantation should not be deferred because of symptom control with beta-blocker therapy alone: breakthrough torsade de pointes during sleep can still be fatal.