A 14-year-old competitive swimmer experiences sudden cardiac arrest during a swimming race. He is successfully resuscitated. His older brother died suddenly at age 17. ECG shows QTc of 530 ms. Genetic testing reveals KCNQ1 mutation. This condition predisposes primarily to which arrhythmia?
- A Catecholaminergic polymorphic ventricular tachycardia (CPVT)
- B Wolff-Parkinson-White associated AF
- C Torsades de pointes (polymorphic VT) ✓
- D Brugada-type ventricular fibrillation
Explanation
KCNQ1 mutation causes Long QT Syndrome type 1 (LQT1) — the most common LQTS subtype. KCNQ1 encodes the IKs channel (slow delayed rectifier potassium current); loss-of-function prolongs repolarization, leading to prolonged QTc (>460 ms in children). LQT1 is specifically triggered by exercise (particularly swimming) and catecholamine surges. The resultant arrhythmia is torsades de pointes — a polymorphic VT that can degenerate into VF causing sudden cardiac death. CPVT is caused by RYR2/CASQ2 mutations with a normal QTc. Brugada is associated with SCN5A mutations and a characteristic ECG pattern. WPW involves accessory pathway reentry.
Reference: Ghai Essential Pediatrics, 10th ed.
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