Long QT syndrome (LQTS) is an inherited disease that affects sodium and potassium channels in the heart, leading to abnormal functioning in the heart's electrical system. Prolongation of the QT interval causes ventricular arrhythmias -- which can lead to sudden cardiac death. Episodes of syncope and arrhythmia can be triggered by extreme emotion, loud noise, or exertion, use of specific medications or by electrolyte imbalance.
LQTS is divided into four major categories: Romano-Ward syndrome, Jervell and Lange-Nielsen syndrome, sporadic LQTS, and acquired LQTS. Romano-Ward syndrome have heart symptoms without any additional organ involvement. In contrast, patients with Jervell and Lange-Nielsen syndrome usually present first with congenital sensorineural deafness, and a prolonged QT is detected later. In sporadic LQTS, the patient who presents with LQTS is the first and only case in the family. These cases are attributed to spontaneous mutation. Acquired LQTS is a syndrome of a prolonged QT that is associated with use of a specific medication or to an electrolyte imbalance.
Once thought to be a rare disease, LQTS may occur in one in every 5,000 persons and may cause 3,000 to 4,000 sudden deaths in children and young adults each year in the USA.
If even 50,000 US cases currently exist, this congenital or acquired disease occurs three times more often than acute lymphoblastic leukaemia (the most common childhood leukaemia), one third as often as cystic fibrosis, and twice as often as phenylketonuria. Large numbers of LQTS cases go undiagnosed due to the complexity of the diagnosis, the variety of presentations, and many clinicians' lack of familiarity with the disease.