Loss-of-function mutation in KCNQ1 reducing the slow delayed rectifier potassium current (IKs) causes congenital long QT syndrome Type 1. Which event most characteristically precipitates arrhythmia in affected patients?

• A Sudden auditory stimuli such as an alarm clock
• B Exercise, particularly swimming ✓
• C Arrhythmia during sleep or at rest
• D Postprandial state after heavy meals

Explanation

LQT1 results from reduced IKs, a current critical for QT shortening during sympathetic activation, so adrenergic stress from exercise, classically swimming, triggers torsades. Sudden auditory stimuli are the hallmark trigger of LQT2 (KCNH2, IKr), and events during sleep or rest characterize LQT3 (SCN5A gain of function). Recognizing the genotype-specific trigger guides counseling on activity restriction and beta blocker choice.

Reference: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 12th ed.

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