Double ventricular response caused by longitudinal dissociation in the his bundle.

Electrocardiograms were taken from a 36-year-old woman with normal sinus rhythm in which 4 types of QRS complexes and 2 types of fusion QRS complexes were found in configuration. To interpret this arrhythmia, we proposed 3 unique mechanisms: a) double ventricular response through the fast pathway mainly directing to the right bundle branch and the slow pathway mainly directing to the left bundle branch, b) longitudinal dissociation in the His bundle, and c) transverse conduction in the lower edge of the dissociation. Although functional longitudinal dissociation in the atrioventricular node has been reported, longitudinal dissociation in the His bundle is a rare arrhythmia.