PAC's with RBBB aberration

These PAC's, indicated by arrows, enter the ventricles and find the right bundle refractory. They therefore conduct with RBBB aberrancy. In most normal hearts the right bundle recovery time is longer than the left bundle's; most aberrancy, therefore, has aRBBB morphology. In some diseased hearts the left bundle may have a longer refractory period resultingin LBBB aberration. Aberrant conduction may alsoinvolve the fascicles of the left bundle