Pediatric emergency medicine trisk 1505 1505

when the patient is at rest is a key to the diagnosis The upper limits of the corrected QT interval (QTc ) (using Bazett formula: QTc = (QT)/√RR interval) are 480 msec may be suggestive of LQTS in a patient presenting with syncope There are congenital and acquired causes for a prolonged QT interval The genetic arrhythmia syndromes consist of three subtypes: LQT1, LQT2, and LQT3 The disease occurs due to mutations in genes that encode for cardiac ion channels important in ventricular repolarization Syncope in these patients is related to polymorphic ventricular tachycardia (torsades de pointes) and death is due to ventricular fibrillation One form (LQT3) can also be associated with bradycardia and slow heart rates that may cause syncope Most cases are associated with an autosomal dominant form of the syndrome (i.e., Romano– Ward syndrome), which shows variable penetrance LQT1 is the most common genetic subtype, and the triggers for syncope or sudden death in affected patients include emotional or physical stress, such as diving and swimming One form of LQT1, the Jervell and Lange-Nielsen syndrome, is autosomal recessive and associated with a high risk of sudden death and congenital deafness In LQT2, syncope or sudden death can occur with stress or at rest Cardiac events triggered by sudden loud noises, such as the ringing of an alarm clock, are virtually pathognomonic for this condition Acquired causes for a prolonged QTc interval include hypocalcemia, hypokalemia, hypomagnesemia, hypothyroidism, eating disorders, and the use of drugs that prolong QT interval (e.g., haloperidol, methadone, pentamidine, and sotalol)