Polymorphous ventricular tachycardia associated with normal and long Q-T intervals.

Polymorphous ventricular tachycardia may occur in the setting of either a normal or a prolonged Q-T interval. Torsade de pointes is a form of polymorphous ventricular tachycardia in which the polarity of the QRS complex exhibits phasic alterations in both axis and rate. Traditionally, torsade de pointes has been described in association with a variety of congenital and acquired (including drug and metabolic) causes of Q-T prolongation. The distinction between torsade de pointes and those polymorphous ventricular tachycardias occurring in patients with a normal Q-T interval has important therapeutic implications. The former requires strict avoidance of all drugs that may potentially further delay repolarization, including class I antiarrhythmic agents; immediately, the initiation of cardiac pacing is often necessary for control of arrhythmia, and on a long-term basis, sympathetic nervous blockade is often efficacious. In contrast, the polymorphous ventricular tachycardias with a normal Q-T interval usually respond to conventional therapy, including administration of class I antiarrhythmic agents. Thus, the management of polymorphous ventricular tachycardia should be based on the presence of absence of associated repolarization rather than on the morphologic features of the tachycardia. Unfortunately, recent advances in basic and clinical electrophysiology have not yet elucidated the pathophysiologic basis for these arrhythmias, although this is an area of active investigative interest.