Idiopathic long QT syndrome: association of ventricular tachycardia with alternating left and right bundle branch block.

A case of sporadic long QT syndrome with ventricular tachycardia characteristic of torsades de pointes is presented. The ECG revealed sinus rhythm with marked prolongation (less than 140%) of QT interval and alternating periods of left and right bundle branch block. The onset of ventricular tachycardia was associated with alternating left and right bundle branch block and the disappearance of bundle branch block coincided with the resolution of ventricular tachycardia. This observation suggests the possibility that heterogeneous repolarization of the bundle branch system contributed to ventricular tachycardia either alone or in combination with dispersion of refractoriness of the ventricular myocardium.