QRS alterations produced by auricular and ventricular paroxysmal tachycardia in the presence of bundle branch block patterns: An experimental study in dogs

Abstract

Experimental auricular and ventricular tachycardias have been produced at various sites of the heart in the presence of bundle branch block. The following conclusions can be made: 1. 1. Supraventricular tachycardias do not alter complete bundle branch block patterns significantly. They may, however, increase incomplete types of bundle branch block. 2. 2. Ventricular tachycardias from the ventricle below the intact branch produce bundle branch block patterns from the opposite side. 3. 3. The QRS morphology of ventricular tachycardias from the ventricle below the affected bundle branch depends upon the time of the cardiac cycle in which the stimuli occur. Between the T wave and the beginning of P, complete bundle branch block patterns are produced. Stimuli which fall into the P-R interval fuse with the activation wave coming from the auricle through the unaffected branch and result in narrowed or relatively normal QRS complexes. Fusion beats can be seen which exhibit the typical morphology of the WPW syndrome if the ventricular stimulus is discharged immediately after the P wave.