Coexistence of congenital long QT syndrome and autonomic dysregulation in children.

Loss of consciousness (LOC) in long QT syndrome (LQTS) patients can be caused by torsade de pointes (TdP) or vasovagal syncope (VVS). On genetic testing and head-up tilt testing (HUTT), we diagnosed three young patients with both genotyped LQTS and autonomic dysregulation. According to grade of prolongation of QT interval and LOC status, syncope episodes in two patients were classified as due to VVS, while those of the other patient were due to TdP. We also diagnosed one patient with postural orthostatic tachycardia syndrome. Syncope in LQTS patients should not automatically be labeled TdP. If there is a possibility of VVS, HUTT should be performed, but careful observation is required because TdP cannot be completely ruled out.