Wandering atrial pacemaker: In this condition there are multiple atrial pacemakers, one may or may not be in the SA node (Figure 23). The R-R and P-R intervals are of variable length, depending upon the rate of each pacemaker and its location relative to the AV node. Some P waves may be inverted, indicating the firing of a pacemaker near the AV node and that depolarization of the atria occurred in a retrograde manner.