Which rhythm is characterized by P waves with at least three different morphologies and an irregular atrial rhythm with a regular ventricular rhythm, typically at rate <100 bpm?

• A. Atrial Fibrillation
• B. Atrial Flutter
• C. Wandering Atrial Pacemaker
• D. Multifocal Atrial Tachycardia

Answer: (C)

The rhythm tested is wandering atrial pacemaker. The hallmark is P waves that vary in morphology—at least three different shapes before successive QRS complexes—because the impulse origin is shifting among sites in the atria. This causes an irregular atrial rhythm, but the ventricular rhythm stays regular since the AV node conducts impulses in a consistent pattern, and the overall rate is typically below 100 bpm. If the rate were higher (over 100 bpm) with the same P-wave variability, it would point to multifocal atrial tachycardia. If there were no distinct P waves at all and the rhythm were irregularly irregular, it would be atrial fibrillation, while sawtooth flutter waves with a relatively fast atrial rate would suggest atrial flutter.