Exercise-related QT interval shortening with a peaked T wave in a healthy boy with a family history of sudden cardiac death.

An asymptomatic 15-year-old boy, who had a family history of sudden cardiac death, was referred for screening for cardiac disease. The 12-lead electrocardiogram at rest showed a short QT/QTc(Bazett)/QTc(Fredericia) interval of 320/388/364 ms, but the intervals were further shortened to 200/339/284 ms after the treadmill test concomitant with appearance of a peaked T wave. Other conventional cardiac examinations were normal, but effective refractory period was less than 180 ms in both ventricles, and double ventricular extrastimulation reproducibly induced nonsustained polymorphic ventricular tachycardia. Intravenous administration of epinephrine also induced a short QT interval and a peaked T wave, and a hump was manifested on the T wave of the first postpacing beat with a longer preceding R-R interval. Furthermore, a couple of premature ventricular complexes originated from a similar timing as the hump. Genetic analysis did not show the mutation in KCNQ1, KCNH2, KCNE1, KCNE2, KCNJ2, SCN5A genes but revealed single nucleotide polymorphism (C5457T) in SCN5A gene.