Dual-morphology Bundle Branch Re-entrant Ventricular Tachycardia in Non-dilated Cardiomyopathy.

Bundle branch re-entrant (BBR) tachycardia is an uncommon form of ventricular tachycardia (VT). This arrhythmia typically occurs in patients with a structural heart disease, especially dilated cardiomyopathy, and significant conduction system impairment, although affected patients with a structurally normal heart or normal conduction system have been reported. The QRS morphology during tachycardia can vary; it typically has a left bundle branch block (LBBB) morphology in which the antegrade conduction is over the right bundle and the retrograde limb is over the left bundle. The reverse of this circuit results in a right bundle branch block (RBBB) QRS morphology. A re-entrant circuit also can utilize interfascicular conduction, such as antegrade conduction over the left anterior fascicle and retrograde conduction up the left posterior fascicle or vice versa. Although there are reports of BBR tachycardia and interfascicular VT occurring in the same patient, to our knowledge, there are no prior reports of BBR tachycardia that has both LBBB and RBBB morphologies in the same patient. This case illustrated a BBR tachycardia with both left bundle and right bundle branch morphologies occurring in a patient with a non-dilated left ventricle.