Neurally Mediated Syncope in a Patient with Long QT Syndrome

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A 23-year-old female was referred for evaluation of syncope associated with standing for a long time at a morning gathering. She had experienced 2 episodes of syncope and frequent episodes of pre-syncope at morning gathering. Head-up tilt test demonstrated decrease in blood pressure from 104/65 to 55/28 mmHg and heart rate from 69 to 40 bpm associated with pre-syncope 15 min after the table was tilted upright to a 70° angle. Furthermore epinephrine stress test was performed because electrocardiogram showed prolongation of corrected QT interval of 546 msec. With epinephrine infusion, QT interval prolongation of 48 msec that was sensitive and specific marker for LQT1 was observed. Genetic testing identified KCNQ1, A525V mutation that is associated with LQT1. Since starting propranolol, QT interval was shortened from 546 to 492 msec and she has had no symptom. This case emphasizes the importance to exclude possibility of long QT syndrome in patients with neurally mediated syncope.