A 16-year-old boy has recurrent syncopal episodes that occur exclusively during sleep and at rest. His ECG shows a long isoelectric ST segment with a late-peaking, narrow-based T wave and a QTc of 540 ms. Genetic testing confirms a mutation affecting the cardiac sodium channel SCN5A. Which statement about his condition is correct?
- A Beta blockers are highly effective and the mainstay of therapy
- B This pattern is typical of LQT2, which responds well to nadolol
- C Events triggered at rest with a late-peaking T wave suggest LQT3, where mexiletine may be added and beta blockers are less effective ✓
- D His episodes would be expected to occur during swimming or exertion
Correct answer: C. Events triggered at rest with a late-peaking T wave suggest LQT3, where mexiletine may be added and beta blockers are less effective
Explanation
Rest and sleep trigger events in LQT3, caused by a gain-of-function sodium channel mutation producing persistent inward current and a characteristically long isoelectric ST segment with a late-peaking narrow T wave. Beta blockade is less effective in LQT3 than in other genotypes, and mexiletine, a sodium channel blocker that shortens the action potential, is used as an adjunct. Swimming and auditory triggers point instead to LQT1 and LQT2 respectively, killing those distractors.
Reference: Park's Pediatric Cardiology for Practitioners, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.