745-6 Inherited Disorder with Exercise-induced Ventricular Tachycardia and Sudden Death in Young Adults Mimicking Long QT Syndrome

Abstract

The idiopathic long OT syndrome (LOTS) has familial presentation with prolonged OT interval, stress- and emotion-related syncopal spells and sudden death in young age. We describe a family of 53 members in four generations of whom 5 had died suddenly between ages 16 and 28, and 7 others had experienced syncope. Of them, 11/12 had the events known to be exercise- or anxiety-related. The corrected QT interval was abnormal, 450–470 ms, in 5 and normal (≤ 440 ms) in another 5 of the affected. During treadmill exercise stress test runs of polymorphic ventricular tachycardia of non-torsade type (sustained in 1) emerged at heart rates above 110–140/min in 6/8 of the tested. Left ventricular wall motion and thickness were normal in echocardiography, and right ventriculography yielded normal results. In all 5 autopsied, right ventricular size was normal without aneurysmal formations. Mild to moderate interstitial fibrosis of the myocardium appeared in 2 autopsied and in endomyocardial biopsy in 5/6 of the examined. Family pedigree indicated an autosomal dominant inheritance. Symptoms or arrhythmias in exercise test occurred in 12/41 subjects older than 12 years and in 0/12 subjects below that age, suggesting manifestation first after childhood. In conclusion, this familial cardiac disorder resembles long OT syndrome in presentation but differs from it by only marginally prolonged OT interval and by almost universal emergence of ventricular tachycardia during exercise. The disorder may be misdiagnozed as idiopathic long OT syndrome without performing an exercise test and endomyocardial biopsy, and may avoid recognition before adolescence.