A 14-year-old boy presents with episodic palpitations, near-syncope, and a family history of sudden cardiac death in a young uncle. ECG shows corrected QT interval (QTc) of 520 ms. Which ion channel mutation is MOST commonly associated with congenital long QT syndrome type 1 (LQT1) and what triggers are characteristically associated?
- A KCNH2 (HERG, IKr channel) — triggered by auditory stimuli/sleep
- B KCNQ1 (IKs channel) — triggered by swimming/exercise ✓
- C SCN5A (INa channel) — triggered during sleep/rest
- D CACNA1C (L-type calcium channel) — triggered by emotional stress
Explanation
LQT1 is caused by loss-of-function mutations in KCNQ1 encoding the slow delayed rectifier potassium channel (IKs), resulting in decreased repolarizing current and prolonged QT. LQT1 events are classically triggered by exercise and swimming (adrenergic stimulation reduces repolarization reserve further when IKs is already impaired). LQT2 (KCNH2/HERG) events are triggered by auditory stimuli, emotion, or sleep. LQT3 (SCN5A, gain-of-function Na channel) events occur predominantly during rest/sleep. This is a critical distinction for clinical management: beta-blockers are most effective in LQT1 but only modestly effective in LQT3.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.