A wandering pacemaker is an atrial arrhythmia resulting from a constant change in pacemaker sites between the SA node, atria, and AV junction (see Figure 4.1). The resulting rhythm shows a combination of sinus and atrial beats. 

If the impulse is generated from the SA node, the resulting P wave is smooth and rounded on the ECG. When the impulse drops to the atria, the P wave is flattened, notched, or biphasic. If the pacemaker drops even lower to the AV junction, then the P wave may be inverted or possibly absent. 

The PR interval varies as the pacemaker changes from the SA node to the atria or AV junction. The QRS complex usually has a normal duration since the rhythm originates above the ventricles.

Characteristics of a Wandering Pacemaker 

1. 1. Slightly irregular rhythm
      • The R-R intervals vary slightly because of changes in the pacemaker site
   2. Rate: 60–100 bpm
   3. P wave morphology varies
   4. P wave does appear in front of the QRS complex
   5. PR interval: < 200 milliseconds
      • May be abnormally short: < 120 milliseconds
      • Varies as the pacemaker site changes
   6. QRS complex normal: < 120 milliseconds

Figure 4.1. Wandering Pacemaker

P wave morphology with a slight irregularity of the R-R interval.