Long-QT syndrome and channelopathies — branching viva

Examiner opening (Examiner)

You are the general paediatric registrar in the emergency department. A nine-year-old girl is brought in after collapsing during a school swimming carnival. She was pulled from the pool unconscious, jerked briefly, and recovered fully within two minutes. Her twelve-lead ECG shows a QTc of 520 milliseconds, and her mother mentions she has fainted "all her life." The team is arranging a CT head and an EEG. Talk me through your assessment and management. [1]

Exemplar opening (Candidate)

This child has high-probability long-QT syndrome, and the team is misdirecting the workup toward a neurological cause when this is a cardiac arrhythmia. The QTc of 520 milliseconds is diagnostic of long-QT syndrome regardless of symptoms — a QTc above 500 milliseconds confers high risk of arrhythmic events. The collapse during swimming is the classic trigger for LQT1 (KCNQ1 mutation), and the maternal history of fainting is a family history clue suggesting an inherited arrhythmia syndrome. The seizure-like movements are the cerebral hypoxia of a transient arrhythmia — torsades de pointes that self-terminated — not epilepsy. My immediate plan is to admit her for cardiac monitoring, stop any QT-prolonging medications, check and correct electrolytes (particularly potassium above 4.0), restrict her from swimming and sport, and refer urgently to the inherited cardiac conditions service for genetic testing and definitive management. The CT head and EEG are not the priority. [1] [2]