In long QT syndrome (LQTS), the sodium channel mutation (LQT3 due to SCN5A) has a specific clinical characteristic regarding arrhythmia timing that distinguishes it from LQT1 and LQT2:
- A Events occur predominantly at rest or during sleep (bradycardia-dependent) ✓
- B Events triggered by exercise (adrenergic-dependent)
- C Events triggered by sudden auditory stimuli or emotional stress
- D Events occur only in females during menstruation
Explanation
LQT3 (SCN5A gain-of-function mutation — persistent sodium current) is bradycardia-dependent and events occur characteristically at REST or during SLEEP when heart rate is slow, prolonging QT interval and favouring EADs (early afterdepolarisations). LQT1 (KCNQ1, IKs) events occur during exercise/swimming (adrenergic activation). LQT2 (KCNH2, IKr) events triggered by sudden auditory stimuli or emotional stress. LQT3 carries the highest risk per event despite lower overall event frequency. Management includes sodium channel blockers (mexiletine) and ICD in symptomatic patients.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.