Digitalis-induced bundle-branch ventricular tachycardia studied by electrode catheter recordings of the specialized conducting tissues of the dog.

Electrode catheter recordings of the bundle of His (H), the right bundle branch (RB) and the left bundle branch (LB) were obtained in 15 dogs without thoracotomy during sinus rhythm and digitalis-induced ventricular tachycardia. During sinus rhythm an H-RB-LB sequence was recorded. This sequence was unchanged during atrial stimulation at rapid rates or during cardiac slowing by vagal stimulation. In 10 of 15 cases of digitalis-induced ventricular tachycardia the LB potential preceded the onset of ventricular depolarization (QRS), and an LB-H-RB sequence was recorded. These findings indicated that during ventricular tachycardia the pacemaker was located in the left bundle branch and the bundle of His was retrogradely depolarized. In 5 of 15 cases of digitalis-induced ventricular tachycardia the H, LB and RB potentials were recorded after the onset of ventricular depolarization. These findings suggested that the pacemaker was located in the Purkinje fibers.