Wandering atrial pacemaker

A wandering atrial pacemaker is present when there are multiple ectopic foci within the atrial myocardium that serve as dominant pacemakers. There is a changing vector of atrial activation which causes a changing P wave morphology and PR interval duration. The QRS intervals have very variable cycle lengths since the ectopic foci have differences of automaticity and rates of impulse generation. The rhythm is therefore irregularly irregular. QRS morphology is not altered from that seen during sinus rhythm, since activation of the ventricular myocardium occurs normally via the His-Purkinje system.

The normal P wave in sinus rhythm is slightly notched since activation of the right atrium precedes that of the left atrium. The P wave is upright in a positive direction in leads I and II. A P wave with a uniform morphology precedes each QRS complex. The rate is between 60 and 100 beats per minute and the cycle length is uniform between sequential P waves and QRS complexes. In addition, the P wave morphology and PR intervals are identical from beat to beat.