Left-sided intraventricular conduction delay concealed by right bundle branch block.

The electrocardiograms of a 69-year-old woman with severe heart failure showed a left-sided nonspecific intraventricular conduction delay (QRS duration, 0.13 seconds) characterized by notches and slurrings in the descending part of the R waves in the left precordial leads and in the ascending parts of the S waves in the right precordial leads. Subsequently, a complete right bundle branch block with wider QRS complexes (0.17 seconds) appeared. It is possible to consider that the left-sided nonspecific intraventricular conduction delay was concealed by the greater conduction delay occurring when the complete right bundle branch block was present. This would be in keeping with a previous study using Doppler tissue imaging in which this was postulated but where the corresponding electrocardiograms were not shown.