Wandering Atrial Pacemaker: The Classical Definition

Traditionally, WAP was considered to be a rhythm created when the pacemaking function of the heart swung back and forth between the sinus node and some ectopic site. The resulting rhythm strips showed a variation in P-wave morphology, along with a slight variation in the regularity of the complexes. This presentation was very similar to a sinus arrhythmia but with varying P-wave morphology.

In reality, we now know that this type of WAP is due to a swinging of the pacemaking site within the sinus node itself. Remember on page 130, we discussed the fact that the P waves in normal sinus rhythm can vary by a slight amount morphologically because of some slight variations in the exact point of origin of the atrial impulse (Figure 17-1). Well, the traditional definition of a WAP is an exaggeration of this mechanism.

Figure 17-1 P waves in normal sinus rhythm can vary by a slight amount morphologically because of some slight variations in the exact point of origin of the atrial impulse.

© Jones & Bartlett Learning.

The sinus node is an elongated structure within the atria. Respiratory variation and metabolic changes that occur as a result of respiration can cause a temporary fluctuation of the main pacemaking area that actually stimulates the impulse. During those periods when the heart rate is faster on the rhythm strip (inspiration), the pacing area is at the higher end of the node and the resulting P wave on the strip is taller with a longer PR interval. During slower parts of the rhythm (expiration), the pacing area is lower down on the node and the resulting P wave is shorter, with a shorter PR interval. This explains why the WAP rhythm, classically defined, is very similar to sinus arrhythmia (Figure 17-2). It is basically just an exaggerated response of the same processes.

Figure 17-2 Wandering atrial pacemaker.

From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.