Long QT syndrome (LQTS) is prolonged duration of the QT interval in the cardiac cycle. This syndrome can be congenital or acquired. The congenital form may or may not be accompanied by deafness. Both forms have a propensity for ventricular dysrhythmias, which in turn may lead to unstable dysrhythmias (e.g., torsades de pointes, ventricular fibrillation), syncope, cardiac arrest, and/or sudden death.

The true incidence of LQTS is difficult to estimate. It can be acquired or congenital, as a result of genetic mutations; approximately 10% to 15% of gene mutation carriers have normal QT _C duration. Overall, LQTS may occur as frequently as 1:3000 to 1:5000.

The congenital form of LQTS is the result of the mutation of cardiac ion channel genes. Thus far six chromosomal mutation locations and five specific genes have been identified. There are six variants of LQTS associated with Romano-Ward syndrome and two variants associated with Jervell and Lange-Nielsen syndrome. The prolongation of the QT interval occurs when the myocardial cells become overloaded with positively charged ions during the process of ventricular repolarization. This prolongation predisposes the patient to unstable ventricular dysrhythmias, particularly torsades de pointes, ventricular fibrillation, and sudden cardiac death. The appearance of ventricular dysrhythmias may be precipitated by any of a large number of adrenergic stimuli, including exercise, emotion, loud noises, atnd startle, but may occur spontaneously without preceding conditions or triggers. As a result, the patient with LQTS should be generally discouraged from participation in competitive sports.

LQTS can be acquired as a result of ingestion of various medications. The complete list of medications that may produce LQTS and/or an incidence of torsades de pointes is too large to be included in this volume, but it includes amiodarone, erythromycin, methadone, procainamide, and quinidine. A complete list of the medications can be found at www.qtdrugs.org/medical-pros/drug-lists/list-01.cfm.