The shift may be within the sinus node itself, a manifestation of the multi-centric nature of the cluster of pacemaker sites. In this situation, the change in P wave morphology will be relatively minor since the normal leftward, inferior and anterior/posterior direction of the P wave spatial vector will be maintained. This ECG strip is from an ambulatory ECG recorded in a younger patient. It illustrates a change in P wave morphology between the first two and the last three beats. This may reflect a shift of the pacemaker with the sinus node itself, but could also be due to an ectopic atrial pacemaker whose rate is very similar to that of the sinus pacemaker