The presence of multiple P wave morphologies indicates multiple ectopic pacemakers within the atria and/or AV junction. If ≥ 3 different P wave morphologies are seen, then multifocal atrial rhythm is diagnosed: If ≥ 3 different P wave morphologies are seen and the rate is ≥ 100, then multifocal atrial tachycardia (MAT) is diagnosed:

The P wave is a summation wave – electrical activity that comes from successive signaling from multiple points, causing wave-like contractions. These multiple points contain pacemaker cells that generate action potentials independently of the CNS.