Prolonged QT-Interval Syndromes

PROLONGATION of the QT interval, either on a congenital or an acquired basis, is associated with an increased likelihood of malignant ventricular arrhythmias.1-3Patients with QT prolongation frequently develop recurrent attacks of syncope or may present with sudden death. The malignant ventricular arrhythmias are characterized by rapid, irregular tachycardias that usually have a polymorphous configuration or a torsades de pointes pattern. The latter is a French term that describes the tachycardia as a "twisting of the points," so called because the QRS axis shifts back and forth around the baseline. Although polymorphous ventricular tachycardia and torsade frequently occur in the setting of QT prolongation, these malignant arrhythmias may also occur in the absence of a repolarization abnormality. Effective cardiac output and blood pressure are markedly impaired during torsades de pointes, with resultant syncope. Most tachyarrhythmic episodes terminate spontaneously with return of consciousness, but some may degenerate into ventricular fibrillation,